SDCCH_Dimensioning

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Planning Guideline: SDCCH dimensioning

Issued by Communication Mobile Networks Com MN PG NT NE 1 Munich

© SIEMENS AG 2005 The reproduction, transmission or use of this document or its contents is not permitted without express written authority. Offenders will be liable for damages. All rights, including rights created by patent grant or registration of a utility model or design, are reserved. Technical modifications are possible. Technical specifications and features are binding only in so far as they are specifically and expressly agreed upon in a written contract.

s Contents 1.1 1.2 1.3 2

HISTORY...................................................................................................................... 4 REFERENCES ............................................................................................................... 4 ABBREVIATIONS, DEFINITIONS AND EXPLANATIONS................................................... 5

GENERAL INFORMATION ....................................................................................... 10 2.1 2.2

INTRODUCTION .......................................................................................................... 10 DEFINITIONS.............................................................................................................. 11

3

INTRODUCTION TO STANDALONE DEDICATED CONTROL CHANNEL ... 12

4

FEATURES RELATED TO SDCCH .......................................................................... 16 4.1 SDCCH HANDOVERS ................................................................................................ 16 4.2 DIRECT TCH ASSIGNMENT ....................................................................................... 18 4.3 CELL BROADCAST CHANNEL .................................................................................... 18 4.4 SMOOTH CHANNEL MODIFICATION ........................................................................... 19 4.4.1 SDCCH allocation in case of SCM .................................................................. 22 4.4.2 TCH allocation in case of SCM........................................................................ 23 4.4.3 Recommendations for configuration of TCHSDs for SCM .............................. 23

5

SDCCH CONFIGURATIONS...................................................................................... 24 5.1 5.2 5.3 5.4 5.5 5.6 5.7

6

SIGNALING EVENTS WHICH REQUIRE SDCCH RESOURCES ...................... 30 6.1 6.2 6.3 6.4 6.5 6.6 6.7 6.8 6.9

7

SDCCH/4 ................................................................................................................. 24 SDCCH/8 ................................................................................................................. 24 POSSIBLE CHANNEL CONFIGURATIONS WITH SDCCH ............................................... 25 SDCCH WITH CBCH................................................................................................ 27 SDCCH IN CASE OF DUAL BAND STANDARD CELL .................................................. 28 SDCCH LIMITATIONS ............................................................................................... 29 LIMITATIONS OF CHANNEL TYPE TCHSD.................................................................. 29 CALL SETUP............................................................................................................... 30 LOCATION UPDATE ................................................................................................... 30 PERIODIC REGISTRATION (PERIODIC LOCATION UPDATE)......................................... 31 SHORT MESSAGE SERVICE ........................................................................................ 31 SUPPLEMENTARY SERVICES MANAGEMENT .............................................................. 32 UNSTRUCTURED SUPPLEMENTARY SERVICE DATA ................................................... 32 IMSI ATTACH / DETACH ........................................................................................... 32 LOCATION REQUEST.................................................................................................. 33 PHANTOM RACH...................................................................................................... 33

SDCCH CHANNEL PLANNING AND DIMENSIONING....................................... 35 7.1 SDCCH SEIZURE TIMES ............................................................................................ 38 7.2 SDCCH LOAD GENERATED BY SUBSCRIBER .............................................................. 39 7.2.1 Call attempt ...................................................................................................... 39 7.2.2 Location Update............................................................................................... 39 7.2.3 Periodic Registration (Periodic Location Update).......................................... 39 7.2.4 SMS................................................................................................................... 40 2


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s 7.2.5 Location Request .............................................................................................. 40 7.2.6 IMSI Attach/Detach.......................................................................................... 40 7.3 REQUIRED AMOUNT OF SDCCH RESOURCES PER CELL ............................................. 40 7.3.1 Mixture of HR and FR...................................................................................... 47 8

DIMENSIONING EXAMPLES.................................................................................... 51 8.1 EXAMPLE OF MIXTURE OF FR AND HR...................................................................... 51 8.1.1 Example using values from HR/FR tables........................................................ 51 8.1.2 Complete calculation (without HR/FR tables) ................................................. 52 8.2 DIMENSIONING EXAMPLE OF SMS CELL BROADCAST IMPLEMENTATION.................. 56 8.3 SDCCH IN CASE OF DUAL BAND STANDARD CELL .................................................. 59

9

APPENDIX A: SIEMENS TRAFFIC MODEL .......................................................... 62

10

APPENDIX B: DESCRIPTION OF MESSAGES USED IN MESSAGE FLOWS 63

11

APPENDIX C: USE CASE: SDCCH CREATION FOR A CELL ....................... 65

12

APPENDIX D: PARAMETERS AND SETTINGS ................................................ 66

12.1 12.2 13 13.1 13.2 13.3 13.4 13.5 13.6

SIEMENS BSS PARAMETERS RELEVANT FOR SDCCH CHANNEL ................................ 66 PARAMETERS FOR SMOOTH CHANNEL MODIFICATION .............................................. 67 APPENDIX E: PERFORMANCE MEASUREMENTS AND COUNTERS........ 68 SDCCH RELATED MEASUREMENTS ........................................................................... 68 TCH AND SDCCH ASSIGNMENT RELATED MEASUREMENTS ................................... 68 RELEASE AND LOSS OF DEDICATED CONNECTIONS RELATED MEASUREMENTS........ 69 HANDOVER RELATED MEASUREMENTS .................................................................... 69 MISCELLANEOUS MEASUREMENTS ........................................................................... 70 SCM RELATED MEASUREMENTS .............................................................................. 70

3 Planning Guideline: SDCCH dimensioning

s

s 1.1

History

Version 1.0

1.2

Date 07.2006

Chapter(s) All

Changes / Reasons First version of document.

References

The following documents are relevant and will be used as references in the forthcoming chapters of this document: [CML]

Command Manual, CML: BSC, BR8.0

[PMMF]

Performance Measurement, PM: SBS Message Flows BR 8.0

[PMC]

Performance Measurement, PM: SBS Counters, BR8.0

[DB]

SBS BSC Database Parameter Description BR8.0


s

s 1.3

Abbreviations, Definitions and Explanations

Abbreviations and definitions used throughout the document are explained in the table below. Abbreviation

Definition, explanation

3GPP

3rd Generation Partnership Project

Abis

Interface between BSC and BTSE(s)

AGCH

Access Grant Channel

BSDCCH

Blocking rate on SDCCH channel

Bsignaling

Blocking rate for signaling

BTCH

Blocking rate on TCH channels

BBSIG

Baseband and Signaling board

BCCH

Broadcast Control Channel

BER

Bit Error Rate

BH

Busy Hour

BSC

Base Station Controller

BSSMAP

Base Station Management Application Part

BTSE

Base Transceiver Station Equipment

capSDCCH

Capacity of SDCCH channels (= number of Erlangs that can be conveyed by all SDCCH sub-channels (usually per cell))

capTCH

Capacity of TCH channels (= number of Erlangs that can be conveyed by all TCHs (usually per cell))

CB

Call Barring

CBC

Cell Broadcast Centre

CBCH

Cell Broadcast Channel

CBS

Cell Broadcast Services

CCCH

Common Control Channel

CCH

Control Channel

CF

Call Forwarding

CITA

Cell Identifier Timing Advance

CLIR

Calling Line Identification Restriction

CS

Circuit Switched

CU

Carrier Unit 5


s

s Abbreviation


DCCH

Dedicated Control Channel

DL

Downlink

DR-TCH

Dual Rate TCH (Full Rate or Half Rate)

DT1

Data Form 1; SCCP Message

DTAP

Direct Transfer Application Part

Erl

Erlang

fErlangB

Erlang B formula

FACCH

Fast Associated Control Channel

FR

Full Rate

FR%

Full Rate percentage

FRTRUNKS

Number of Full Rate trunks

HLR

Home Location Register

HO

Handover

HR

Half Rate

HRTRUNKS

Number of Half Rate trunks

IF

Interface

IMEI

International Mobile Equipment Identification

IMSI

International Mobile Subscriber Identity

KPI

Key Performance Indicators

LA

Location Area

LAPD

Link Access Procedure on the D channel

LAPDm

Link Access Protocol on Dm Channel; Maintenance information exchange

LCS

Location Services

loadsub,SDCCH

SDCCH load per subscriber

loadsub,TCH

TCH traffic per subscriber

LPDLR

LAPD Link Radio Signaling

LR

Location Request

LUP

Location Update

MOC

Mobile Originating Call attempt

MS

Mobile Station

MSC

Mobile Switching Center 6


s

s Abbreviation


MSLS

Multi Service Layer Support

MTC

Mobile Terminating Call attempt

NCA/sub, BH

Number of Call Attempts per subscriber per Busy Hour

NLR

Number of Location Requests per subscriber and BH

NLUP

Number of Location Updates per subscriber and BH

NMOC

Mobile Originating Call attempts per subscriber and BH

NMTC

Mobile Terminating Call attempts per subscriber and BH

NP-LUP

Number of Periodic Location Updates per subscriber and BH

NSMS

Number of SMS messages per subscriber and BH

NSS/USSD

Number of SS/USSD messages per subscriber and BH

NTRX, cell

Number of TRXs per cell

PCH

Paging Channel

PLMN

Public Land Mobile Network

PM

Performance Management

RACH

Random Access Channel

RR

Radio Resources

RSL

Radio Signaling Link

RSSI

Received Signal Strength Indicator

RxLevel

Receive Level

RxQual

Receive Quality

SACCH`

Slow Associated Control Channel

SBS

Siemens BSS System

SCCP

Signaling Connection Control Part

SCI

Subscriber Controlled Input

SCM

Smooth Channel Modification

SDCCH

Standalone Dedicated Control Channel

SDCCH/4

One of 4 SDCCH/4 sub-channel in combined configuration or group of SDCCH/4 sub-channels within combined configuration

SDCCH/8

One of 8 SDCCH/8 sub-channel in uncombined configuration or group of SDCCH/8 sub-channels within one TS

SDCCHLOAD

A variable corresponding to amount of SDCCH load in a cell for certain number of subscribers 7


s

s Abbreviation


SDCCHSUB-CHANNELS Number of SDCCH sub-channels SDCCHTS

Number of SDCCH timeslots

SLL

Service Layer List

SMLC

Serving Mobile Location Centre

SMS

Short Message Service

SNIR

Signal to Noise and Interferer Ratio

SOVA

Input Soft decision Value for the decoder

SS

Supplementary Services Management

STM

Siemens Traffic Model

subSDCCH

Subscriber capacity of SDCCHs (= number of subscribers that can be served by SDCCHs)

subTCH

Subscriber capacity of TCHs (= number of subscribers that can be served by TCHs)

tcall setup

The time an SDCCH is seized by an call setup

tLR

The time an SDCCH is seized by an Location Request

tLUP

The time an SDCCH is seized by an Location Update

tSMS

The time an SDCCH is seized by an SMS message

tSS/USSD

The time an SDCCH is seized by a SS/USSD message to be sent

Tmh

Mean holding time

TCH

Traffic Channel

TCHtraffic

A variable corresponding to amount of traffic in a cell for certain number of subscribers

TCHTRUNKS

Number of TCH trunks

TEI

Terminal Endpoint Identifier

TMSI

Temporary Mobile Subscriber Identity

TRAU

Transcoding and Rate Adaptation Unit

TRX

Transmitter / Receiver

TS

Timeslot

TSFR

Number of TSs for Full Rate traffic

TSHR

Number of TSs for Half Rate traffic

TSsign

Number of TSs for signaling (include SDCCHTS) 8


s

s Abbreviation


TSTCH

Number of TSs for TCH channels

Um

Air interface

UL

Uplink

USSD

Unstructured Supplementary Services Data

VLR

Visiting Location Register

In some equations presented in this document the following symbols are used: Abbreviation

Type


⎣x ⎦

Bracket

Round down of evaluated ‘x’ value, i.e. ⎣π ⎦ = 3

⎡x ⎤

Bracket

Round up of evaluated ‘x’ value, i.e. ⎡π ⎤ = 4


s

s 2

General Information

The purpose of this document is to present SDCCH dimensioning aspects and to serve as a guidebook for dimensioning of signaling channels on air interface for Siemens BSS. This document presents the different possible configurations of SDCCH channels with recommendations which configuration should be used in which case. The document also describes the events and transactions that require the allocation of SDCCH resources. In addition, the mean values of the SDCCH holding times associated to these SDCCH transactions are shown to give a detailed overview of the SDCCH requirements. The document explains in detail how the number of required SDCCH resources must be calculated depending on given conditions and requirements. 2.1

Introduction

Dimensioning examples of SDCCH and TCH channels given in the document are based on Siemens Traffic Model. This traffic model is included in Appendix A: Siemens Traffic Model.


s

s 2.2

Definitions

Few definitions were provided as an introduction to the document in order to avoid misunderstandings in meaning of certain technical terminology. Control channels – denotes channels used for signaling and controlling, like e.g. SCH, BCCH, SACCH, RACH, SDCCH. SDCCH load – a term describing signaling, user data, etc. conveyed by SDCCH channels. Please also refer to definition of the term ‘signaling.’ Signaling – load which is not (directly) generated by subscribers (i.e. measurements, control messages etc.). To describe signaling a term ‘signaling load’ will be used in compare to term ‘traffic’ which will be used only with respect to TCH load. Sub-channel – a term describing one of SDCCH/8 (uncombined configuration) or SDCCH/4 (combined configuration) channels. E.g. one SDCCH/8 channel (which require one radio TS) is composed of 8 SDCCH/8 sub-channels. Sub-slot – term used to describe one HR trunk, where one timeslot can convey two HR trunks. TCH traffic – a term describing, within this document, load conveyed by TCH channels. Please also refer to definition of ‘signaling’. Timeslot - one of 8 TDMA carriers conveyed by one radio carrier (i.e. by one TRX by means of hardware). Traffic – this term denotes carried calls. Term traffic will be used only to describe load generated by user (e.g. TCH traffic). Please compare this description with definition of ‘signaling’. Trunk - traffic channel element that can be used for a single call. This element may be only a subset of a physical channel (timeslot). For example, a HR trunk corresponds to one Halfrate sub-slot of a physical dual rate timeslot (i.e. one timeslot corresponds to two HR trunks or one FR trunk). E.g. one trunk conveys one TCH channel which requires one timeslot in case of Full Rate traffic or half of timeslot in case of HR traffic.


s

s 3

Introduction to Standalone Dedicated Control Channel

The SDCCH load in network consists of call establishments, Location Updates (normal and periodic ones), SMS messages and few other events. The signaling load is conveyed by signaling channels depicted in figures below. As can be seen Standalone Dedicated Control Channel (SDCCH) belongs to Dedicated Control Channel (DCCH) group which belongs to Control Channels (CCH) group:

Figure 1: Logical Channel types

Figure 2: Dedicated Control Channels 12 Planning Guideline: SDCCH dimensioning

s

s An SDCCH channel is required for call establishments in voice services and carries also non-call-associated signaling information, e.g. for mobility management such as Location Updates and Attach/Detach procedures or user data transfers processed via SDCCH, such as SMSs or Supplementary Service management. Additionally, the SDCCH is utilized to support Location Services (LCS). Every call (MOC, MTC) or dedicated transaction (LUP, SMS, IMSI Detach etc.) requires the assignment of a dedicated signaling channel. In mobile originating procedures, the MS starts a connection establishment by sending CHANNEL REQUEST message on the Random Access Channel (RACH). The assignment of a dedicated signaling channel is performed using the IMMEDIATE ASSIGNMENT procedure. Once the network has received the CHANNEL REQUEST message, it reserves an SDCCH sub-channel (if there is an idle SDCCH available) for subsequent signaling and sends IMMEDIATE ASSIGNMENT message on the AGCH channel, which is used to forward this message to MS. If all the SDCCH sub-channels are occupied (busy), the network rejects the SDCCH request by sending an IMMEDIATE ASSIGNMENT REJECT message. The allocated SDCCH channel is used for the security procedures such as authentication and transmission of ciphering parameters and call initialization (exchange of MS capabilities and service requirements). In case of a call (MOC, MTC) a traffic channel is requested and allocated, if available. After successful seizure of the allocated TCH by the MS (or after unsuccessful TCH allocation and seizure), the SDCCH is released. The figure below shows the basic successful message flow of an originating SDCCH request and the subsequent (immediate) assignment procedure that takes place for each call transaction procedure requiring a dedicated control channel (assuming that Direct TCH Assignment is disabled). A short description of message acronyms used in the presented message flows can be found in chapter 10: Appendix B: Description of messages used in message flows. Please do also refer to customer document [PMMF] (Performance Measurement, PM: SBS Message Flows) for further message flows and details about transactions performed on a SDCCH.


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Figure 3: Signaling procedure for CS during mobile originating call

A similar procedure takes place in Mobile Terminating Call. A PAGING REQUEST message is sent on the PCH channel (broadcast message) to the cells within the Location Area in which the called MS performed the last Location Update, in order to find appropriate MS in one of the cells associated to the Location Area. When called MS receives PAGING REQUEST message, it sends CHANNEL REQUEST via RACH (just like in originating mobile) in order to transmit the PAGING RESPONSE to the network via the dedicated control channel. If an unoccupied SDCCH is available, the network grants the SDCCH by sending a corresponding IMMEDIATE ASSIGNMENT message on the AGCH. In downlink direction the AGCHs and PCHs share the same CCCH resources on radio interface. This means that the same resources (CCCH blocks) are used for transmission of PAGING REQUEST message (on PCH channel) and IMMEDIATE ASSIGNMENT messages.


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Figure 4: Signaling procedure for CS during mobile terminating call

For further details related to message flows please refer to customer document [PMMF] (Performance Measurement, PM: SBS Message Flows).


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s 4

Features related to SDCCH

The following sub-chapters describe the most relevant signaling features that impact the SDCCH channel load, dimensioning and functionality. 4.1

SDCCH handovers

Usually the seizure time of an SDCCH channel is so short that a channel change via handover is not needed (and also not favourable, especially if the time needed for the signaling and execution of the handover procedure is longer than the SDCCH seizure). SDCCH seizure periods may be longer in particular cases only, e.g. in case of TCH queuing or multiple transmission of SMSs in idle mode, only in these cases SDCCH handover should be considered. SDCCH handover may happen for two main reasons: MS mobility, Bad radio conditions for the seized channel. Because of these reasons different handover types may occur. More detailed possible handovers are presented in the table 1. Moreover no forced SDCCH-SDCCH handover is supported. In case of concentric cells: no SDCCH-SDCCH intracell handover inner complete / complete inner area is possible as in a concentric cell all SDCCHs are configured in the complete area only.

Figure 5: Concentric cell configuration

In case of extended cells: no SDCCH-SDCCH intracell handover near far / far near (single timeslot  double timeslot) is possible as in an extended cell all SDCCHs are configured in the far (double timeslot) area only. The following handover types involving an SDCCH as originating or target channel are possible (and supported): Internal Intracell SDCCH-SDCCH handover: This handover type comprises handovers from SDCCH to SDCCH within the same cell. Internal Intercell SDCCH-SDCCH handover: This handover type comprises: 16 Planning Guideline: SDCCH dimensioning

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s o handovers from an SDCCH in one cell to an SDCCH in another cell managed by the same BSC, o handovers from an SDCCH in one cell to a TCH in another cell (i.e. Directed Retry (1)) managed by the same BSC. MSC-Controlled handover: This handover type comprises: o handovers from an SDCCH in one cell to an SDCCH in another cell managed by a different BSC, o handovers from an SDCCH in one cell to a TCH in another cell (i.e. Directed Retry) managed by a different MSC. Which intercell handover causes are supported when a call is served by an SDCCH (and when intercell SDCCH-SDCCH handover is enabled) is listed in the table below: RxLevel handover

Handover due to low receive level on uplink or downlink. If the receive level is below the minimum threshold handover is necessary.

RxQual handover

Handover due to bad receive quality on uplink or downlink. Bad receive Quality is determined by Bit Error Rate (BER) measurements in the MS and the BTS.

Distance handover Handover due to long distance between MS and BTS. Power budget handover

Handover due to power budget. Power budget handover is a handover to another cell if this cell offers a higher transmission level (irrespective of whether the power level of the actual cell is above the minimum or not).

Fast Uplink handover

Fast Uplink Handover was introduced in BR6.0 as an additional fast handover mechanism that is able to prevent call drops that occur due to a sudden and drastic drop of the UL receive level. Such level drops can occur e.g. in urban areas with small cells and obstacles in the radio path (e.g. buildings). If the level drops too quickly, the standard level handover mechanism is often too slow to ‘rescue’ the call. Table 1: Possible SDCCH handover causes

1 Directed Retry - SDCCH-TCH handover; Because SDCCH channels are usually seized for a short period of time, it is suggested to perform TCH allocation on SDCCH resources in case of no TCH and TCHSD resources. 17 Planning Guideline: SDCCH dimensioning

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s 4.2

Direct TCH Assignment

Direct TCH assignment is a cell specific optional feature. If this feature is enabled the BSC, when it receives an SDCCH request indicating a call (MOC or MTC) in the Establishment Cause embedded in the CHANNEL REQUEST message, tries to allocate a TCH immediately, without allocating an SDCCH first. In this case the FACCH associated to the TCH is used as main control channel for the call setup messages. If the Direct TCH Assignment procedure is disabled, or if the Establishment Cause indicates that no TCH is needed (e.g. the SDCCH request is started for Location Update) or if 'TCH needed' is indicated but there are no TCH resources available, the BSC allocates an SDCCH channel, if available. 4.3

Cell Broadcast Channel

Cell Broadcast Channel (CBCH) is used when Short Message Service Cell Broadcast (SMS-CB) is applied. For this service type, SMS-CB messages are broadcasted via CBCHs within the area where this service is enabled. In this case SMS-CB messages are sent to all MSs in the serving area of BTS. CBCHs use the same physical channel as SDCCHs. If Cell Broadcast is supported, the CBCH will replace one SDCCH sub-channel no matter how the SDCCH was configured (for details concerning SDCCH configuration please refer to chapter 5).

CBC CBS message CBS message

CBS message

MSC

BSC

BTS MS

Figure 6: Cell Broadcast functionality

The feature Short Message Service Cell Broadcast introduces a Cell Broadcast Center (CBC) which sends Cell Broadcast Services (CBS), which are text messages to all MSs in defined area (some part of PLMN). Examples for this kind of messages are weather forecasts, road traffic reports etc. In contrast to standard (point-to-point) SMS messages Cell Broadcast messages do not require acknowledgements from 18 Planning Guideline: SDCCH dimensioning

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s Mobile Stations and thus no dedicated control channel is required. The CBC forwards broadcast messages directly to the BSC, and they are directed to the BTSs over the Abis IF. The BTS periodically sends received information on CBCH channel over air interface. 4.4

Smooth Channel Modification

The Smooth Channel Modification feature supports the dynamic utilization of a radio channel as either TCH or SDCCH depending on the current traffic situation. This allows radio resources to be used for speech, data, signaling and SMS dependent on the current needs without any interruption of other service. Before implementation of this feature it was only possible to configure each radio timeslot either to support TCH or SDCCH manually; a change of the channel type via operator command, led to a reset and thus to a service interruption of the complete associated TRX. The feature SCM avoids SDCCH blocking in cases of large SDCCH loads generated by high signaling load peaks in specific areas (e.g. airports, train stations or PLMN borders). SCM allows the system to flexibly react to SDCCH load which is higher than planned. As a consequence, call setups on the SDCCH are not impacted even when sudden high SMS traffic peaks occur. When operators define timeslots as combined channel type (TCH/SDCCH) the switchover is made automatically without further operator interaction. After configuration by the operator the system automatically adapts the channel configuration to the current traffic situation. This approach avoids also some manual interactions required to change the channel type. The customer selects and configures channels usable as TCH or SDCCH for each carrier. This can be done when new cells are introduced to the network or new carriers are added to a cell. The mentioned 'hybrid' channels (TCH/SDCCH) are created using the channel type TCHSD. When the BSC selects a TCHSD channel for TCH allocation for a specific service (and it selects a hybrid TCH only if all other TCHs or SDCCHs, respectively - depending on whether the TCHSD is to be activated as TCH or SDCCH, are already in state 'busy'), the BTS receives the indication about the current operational mode (TCH or SDCCH sub-channel) within the individual CHANNEL ACTIVATION message. The system can thus dynamically use the timeslot as either a TCH or a SDCCH without further service interruption - the BTS simply activates and operates the channel in correspondence with the channel mode as indicated by the BSC in the CHANNEL ACTIVATION message. Smooth Channel Modification introduces a radio channel pool concept to provide flexible radio resources allocation. Automatic modification of the channel type (e.g. between TCH and SDCCH/8) is performed without operator interaction. If the SDCCH load is higher than a configurable threshold, the TCHSD is automatically re-configured to operate as an additional SDCCH. If one SDCCH sub-channel of this TCHSD is 'busy', the TCHSD cannot be used as TCH anymore and is thus temporarily excluded from the list of idle TCHs in the cell. During creation, each TCHSD is assigned to a specific pool by the operator using the new specific object attribute CHPOOLTYP (for details please refer to [DB]). 19 Planning Guideline: SDCCH dimensioning

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s The following Radio Resource Pools are implemented: Pool

Description

SDCCH_POOL

Contains all the channels configured as SDCCH/4, SDCCH/8 and TCHSD to be used as SDCCH only.

TCH_POOL

Contains all channels declared as Full Rate/Half Rate TCH or TCHSD to be used as TCH only. These TCHs may be used for both CS and PS traffic.

TCHSD_POOL

Contains all the channels created as TCHSD that are seized as dual rate TCH if no TCHs are available in the TCH_POOL anymore. Depending on the SDCCH load, the TCHSD can be moved to the SDCCH_BACKUP_POOL, from where they can be allocated as SDCCH.

SDCCH_BACKUP_POOL

This pool is not configurable and contains the TCHSD sub-channels which have been temporarily moved to the SDCCH_BACKUP_POOL from where they can be allocated as SDCCH. The allocation is, however, only done when all SDCCHs in the SDCCH_POOL are already busy.

Table 2: Pools used by Smooth Channel Modification feature

There is the following correspondence between radio timeslots and Radio Resource Pools: Radio timeslots created as SDCCH automatically belong to the SDCCH_POOL, Radio timeslots created as TCH are automatically belong to the TCH_POOL, Radio timeslots created as TCHSD TS can be configured as belonging to the SDCCH_POOL, to the TCH_POOL or to the TCHSD_POOL.


s

s

TCHPOOL

TCHSDPOOL

SDCCH_BACKUP_POOL

SDCCHPOOL

Full/Half Rate TCH

TCHSD belonging to TCHPOOL

SDCCH/4 or SDCCH/8

TCHSD belonging to SDCCHPOOL TCHSD belonging to TCHSDPOOL

Figure 7: Channel pools for Smooth Channel Modification

Figure 7 shows an example of the relation between pools and channel types. In this example, the following TSs have been created and assigned to the pools: 6 TSs created as TCH (allocated automatically to the TCH_POOL), 8 TSs created as TCHSD (2 TCHSD TSs allocated to TCH_POOL, 2 TCHSD TSs to SDCCH_POOL, and 4 TCHSD TSs to TCHSD_POOL), 2 TSs created as SDCCH (allocated automatically to the SDCCH_POOL). TCHSD_POOL resources are not directly assigned to any service request, but when: The TCH_POOL is congested they are seized as dual rate TCH, or The SDCCH load in the cell has exceeded a configurable load threshold (SDCCH Congestion Threshold - SDCCHCONGTH parameter; for details please refer to [DB]), the first TCHSD is moved (as 8 SDCCH sub-channels) from the TCHSD_POOL to the SDCCH_BACKUP_POOL. When this has taken place, the BSC has created the preconditions that the 8 associated SDCCH sub-channels can be activated for additional SDCCH requests. This however, is done only when all SDCCHs in the SDCCH_POOL are busy, i.e. even with a TCHSD in the SDCCH_BACKUP_POOL the BSC always allocates SDCCHs from the SDCCH_POOL first. As long as the TCHSD is assigned to the SDCCH_BACKUP_POOL, the BSC checks the SDCCH load situation on every release of an SDCCH. When this check establishes that all SDCCHs in the SDCCH_BACKUP_POOL are idle and the SDCCH load has dropped below the configurable threshold, the BSC starts an additional delay timer (TGUARDTCHSD, for details please refer to [DB]). When this timer expires while all SDCCH sub-channels in the SDCCH_BACKUP_POOL are still idle, the TCHSD is moved back to the TCHSD_POOL. 21 Planning Guideline: SDCCH dimensioning

s

s Only TCHSD TSs configured with channel pool type TCHSD_POOL can be allocated either as SDCCH or TCH. TCHSD channel configured with channel pool type TCH_POOL can be used only for TCH support. 4.4.1 SDCCH allocation in case of SCM The algorithm evaluates the SDCCH sub-channel occupancy (also called ‘SDCCH load’). The occupancy is evaluated as the ratio of the busy sub-channels and the sub-channels in SDCCH_POOL and SDCCH_BACKUP_POOL (for details of these calculations please refer to [DB]). Whenever the BSC accesses the 'SDCCH idle list' (pool of available SDCCHs) in a particular cell because it has received an SDCCH request, it checks the current SDCCH load in the cell and compares it against a configurable threshold, represented by the parameter SDCCHCONGTH. If the BSC detects that the current SDCCH load exceeds the threshold SDCCHCONGTH, the BSC moves one TCHSD (the TCHSD with the best interference class is moved first) as 8 additional SDCCH sub-channels from the TCHSD_POOL to the SDCCH_BACKUP_POOL. If the threshold value is high (i.e. SDCCHCONGTH = 100 [%]), a TCHSD TS will be moved from TCHSD_POOL to SDCCH_BACKUP_POOL, only if all the sub-channels in SDCCH_POOL and all SDCCH_BACKUP_POOL are busy, i.e. if the occupancy is 100%. If the threshold value is lower (e.g. 70 [%]), sub-channels will be moved from TCHSD_POOL to SDCCH_BACKUP_POOL even if not required immediately but in order to reserve them for future SDCCH requests. When a SDCCH sub-channel (coming from SDCCH_POOL) is released, the sub-channel is returned to that pool. If the sub-channel to be released comes from SDCCH_BACKUP_POOL and is not the last busy sub-channel in the TCHSD, the sub-channel is returned to the SDCCH_BACKUP_POOL. If the SDCCH load check during the release SDCCH procedure establishes that the current SDCCH load has dropped below the SDCCHCONGTH threshold, a guard timer (parameter TGUARDTCHSD - Guard Timer TCHSD, for details please refer to [DB]) is started for those TCHSDs in the SDCCH_BACKUP_POOL which are in 'idle' mode (no SDCCH sub-channel in state 'busy'). When it expires, the TCHSD is moved back from the SDCCH_BACKUP_POOL to the TCHSD_POOL. The timer TGUARDTCHSD avoids oscillation between TCHSD_POOL and SDCCH_BACKUP_POOL. During the SDCCH allocation the SDCCHs of the SDCCH_POOL are always handled with priority, i.e. an SDCCH request will only be satisfied by a sub-channel from the SDCCH_BACKUP_POOL, if there is no sub-channel available in the SDCCH_POOL. This means that, when the SDCCH load decreases and the congestion in the SDCCH_POOL ends, no SDCCH will be allocated in the SDCCH_BACKUP_POOL anymore.


s

s 4.4.2 TCH allocation in case of SCM In case of TCH Full Rate request, the TCH with the best quality (i.e. the best interference class as indicated by the Idle Channel Measurements) is used from the TCH_POOL. In case of TCH Half Rate request, unpaired channels (with the best interference class) are used first. If the TCH_POOL is empty or congested, the BSC tries to get a TCHSD from the TCHSD_POOL. If both pools are empty or congested, a Directed Retry procedure is attempted for new MOC or MTC. At TCH release the traffic channel is returned to the original pool. 4.4.3 Recommendations for configuration of TCHSDs for SCM As described in chapter 4.4 the feature Smooth Channel Modification deals with unexpected SDCCH load. In other words, SCM allows the system to flexibly react to SDCCH load peaks which exceed the usually managed SDCCH loads in the busy hours. From this point of view the number of TCHSD channels in TCHSD_POOL does not have to be huge, especially considering the fact that one TCHSD in the TCHSD_POOL represents 8 SDCCH sub-channels when moved to the SDCCH_BACKUP_POOL. The required number of TCHSD channels in the TCHSD_POOL should be derived from the SDCCH load and SDCCH blocking KPIs, which can be calculated from PM data of those networks, in which SDCCH load peaks are observed (based on available counters). Another reason which suggests keeping the number of TCHSD channels in TCHSD_POOL not to high, is the possibility of improper radio resources allocation in case of Smooth Channel Modification and Multi Service Layer Support (MSLS) features. This can happen because the BSC will always allocate TCHs from the TCHPOOL from a less-priorized service layer first, before is starts to allocate a TCH from the TCHSD_POOL belonging to a TRX of the higher priorized service layer. Thus, the more TCHSDs in TCHSD_POOL are configured, the less TCHs can be allocated in correspondence with the configured service layer priorities. The suggested basic approach for the number of TCHSD channels in TCHSD_POOL to be configured in a particular cell is the following: 1) Determine the number of required SDCCHs and TCHs in correspondence with the iteration approach as described in chapter 7.3. 2) For each SDCCH (as determined by iteration), create one additional TCHSD in TCHSD_POOL (ideally on a different TRX to avoid LPAD congestions) and take this timeslot from the number of TCH timeslots as determined by iteration. 3) Verify from PM data if further SDCCH blocking situations occur. If yes, additional TCHSDs in TCHSD_POOL should be added step by step. If the configured TCHSD is never seized as SDCCH, then its pool type should be converted to CHPOOLTYP=TCHPOOL.


s

s 5

SDCCH configurations

There are few SDCCH configurations possible depending on requirements and traffic model. 5.1

SDCCH/4

SDCCH/4 consists of 4 dedicated sub-channels for signaling. This channel is mapped on the timeslot used for BCCH (combined configuration of SDCCH and BCCH, also called Combined BCCH). It results in reduced paging capacity on the BCCH channel so this configuration can be used only in areas with low paging load. Only one SDCCH/4 channel can be configured per cell. In the table 3 this channel type is represented by the channel type acronym MBCCHC. A variant of this channel type that reserves one of the 4 SDCCH sub-channels for the CBCH, has the acronym BCBCH. For more details about CBCH please refer to chapter 5.4. 5.2

SDCCH/8

One SDCCH/8 channel carries up to 8 SDCCH/8 sub-channels on one carrier for SDCCH load. As this channel type claims one complete radio timeslot, one SDCCH/8 channel decreases the number of available traffic channels (TCHs) by one. The first configured SDCCH/8 must be defined on the BCCH TRX, further SDCCH channels may be either placed on the BCCH TRX or on further TRXs. It is, however, recommended to distribute the SDCCH channels over different TRXs: Due to redundancy reasons, In order to achieve better load sharing among the Abis LAPD transmit queues which are managed per TRX/LPDLR. The TRX/LPDLR-specific LAPD transmit queue buffers are emptied in a cyclic Round Robin mechanism. As the vast majority of all signaling messages are processed via the SDCCHs, it is recommended to configure the SDCCHs on separate TRXs (to spread SDCCH channels between TRXs). This ensures a harmonized emptying of the LAPD transmit buffers and avoids excessive buffering times or buffer overflow for particular LAPD queues/TRXs. It should be mentioned that SDCCH/4 together with SDCCH/8 configuration is possible. Despite of that this configuration can be used only in areas with low paging because of reduced BCCH capacity. For this reason this configuration (as well as higher configurations using both SDCCH/4 and SDCCH/8, i.e. one SDCCH/4 and 2 SDCCH/8) will not be suggested in this document. This channel type is presented in the table below as a channel with database acronym SDCCH.


s

s 5.3

Possible channel configurations with SDCCH

Possible channel types are presented in table below; channel types containing SDCCH sub-channels are highlighted. SDCCH configurations with CBCH are also presented; they are described in next chapter (chapter 5.4).

Database Acronym

Configuration

TCHFULL

TCH/F + FACCH/F + SACCH/F

MAINBCCH

FCCH + SCH + BCCH + CCCH (AGCH + PCH + RACH)

Main BCCH Combined (BCCH + 4 SDCCH).

MBCCHC

FCCH + SCH + BCCH + CCCH + 4 (SDCCH + SACCH)

Stand-alone Dedicated Control Channel and dedicated control

SDCCH

8 (SDCCH + SACCH)

Channel type Full Rate Channel and associated control Main Broadcast and Common Control Channel

Dual Rate Channel TCHF_HLF

(FR and HR)

HR

TCH/H(0,1) + FACCH/H(0,1) + SACCH/H(0,1)

FR

TCH/F + FACCH/F + SACCH/TF

Broadcast Channel with Cell Broadcast Channel

BCBCH

FCCH + SCH + BCCH + CCCH + 3 SDCCH + 3 SACCH + CBCH

SDCCH Channel with Cell Broadcast Channel

SCBCH

7 SDCCH + 7 SACCH + CBCH

CCCH

BCCH + CCCH

Broadcast and Common Control Channel Half/Full Rate Channel and associated control Full Rate Channel and associated control Stand-alone Dedicated Control Channel and dedicated control

TCH/H(0,1) + FACCH/H(0,1) + SACCH/H(0,1) TCH/F + FACCH/F + SACCH/TF

TCHSD

8 (SDCCH + SACCH)

Table 3: Possible channel types and configurations

Each of the logical channel types listed above requires one radio timeslot. The possible channel combinations can be summarized as presented in table 4. In cells with one TRX, one Combined BCCH (MBCCHC or BCBCH) signaling channel (1 TS) should be used. This configuration is presented as Case 1 in table 4 (values and equations used to determine this statement will be presented in further chapters). When more signaling channels are required it is suggested to use the Uncombined BCCH (channel type MAINBCCH) and SDCCH channels (channel type SDCCH or SCBCH) what leads to Case 2. As stated in the previous chapter, a combination of SDCCH/4 and SDCCH/8 is not recommended. 25 Planning Guideline: SDCCH dimensioning

s

Number of TSs for control channels

s Case

No. of TSs

Timeslot

Channel combination

Case 1

1 TS

1st TS

1 BCCH + 1 CCCH + 4 SDCCH

1st TS

1 BCCH + 1 CCCH

MAINBCCH

Case 2

More than 1 TS

Further TSs

8 SDCCH + 8 SACCH

SDCCH (w/o CBCH) SCBCH (with CBCH)

Database acronym MBCCHC (w/o CBCH) BCBCH (with CBCH)

Table 4: Possible configurations of SDCCH channels

For example in a cell with a single TRX the allocation of timeslots should look like presented in table below. Timeslots from 1st to 7th are configured as traffic channels (TCHs) with associated signaling (FACCH and SACCH; for possible channels configurations please refer to table 3). SDCCH is allocated on timeslot number 0 together with BCCH channel. Timeslot 0

CHTYPE = MBCCHC (FCCH+SCH + BCCH + CCCH + 4 (SDCCH + SACCH))

Timeslot 1...7

CHTYPE = TCHF (TCH/F + FACCH/F + SACCH/F) Table 5: SDCCH configuration with one TRX

In the pictures below for both configurations (e.g. Case 1 and Case 2) the detailed TDMA slot mapping patterns is shown. Figure 8 (Case 1) shows the SDCCH/4 channel with its SACCH channels for both uplink and downlink. With this combined configuration, the BCCH channel includes four SDCCH sub-channels with their SACCHs and three blocks of four timeslots for the CCCH. In the downlink, the PCH and AGCH share the same CCCH blocks. The BCCH channel (physical channel that carries the broadcast channels) always occupies timeslot 0 of carrier. The remaining frames are allocated to the common and dedicated control channels (CCCH and DCCH respectively), for which the operator can use either a combined or a non-combined configuration, depending on the number of carriers in the cell.

Figure 8: Combined configuration of control channels 26 Planning Guideline: SDCCH dimensioning

s

s Figure 9 (Case 2) shows the detailed TDMA slot mapping patterns for an SDCCH/8. As presented in table above, SDCCH/8 channels can be configured starting from the second TS on the BCCH TRX. On the first TS only BCCH/CCCH channels (DL) can be configured. In the non-combined configuration, all the TDMA slots not used for broadcast channels are reserved for the CCCH blocks, therefore at least one additional physical channel must be used as SDCCH. Additional physical channels can, of course, be allocated for the SDCCH.

Figure 9: Non combined configuration of control channels

5.4

SDCCH with CBCH

A Cell Broadcast Channel (CBCH) is used when the feature Short Message Service Cell Broadcast (SMS-CB) is applied in a cell. If the feature is enabled, SMS-CB messages are distributed via the CBCH towards the Mobiles Stations that are configured to receive these messages. CBCHs use the same physical channel as SDCCHs. If SMS-CB is supported, the CBCH will “steal” one SDCCH sub-channel, no matter how the SDCCH channels were configured. In detail, the numbers of SDCCH channels from configurations described above are reduced by one in order to allocate one CBCH channel:

Channel type

Database Acronym

Configuration

SDCCH capacity

Broadcast Channel with Cell Broadcast Channel

BCBCH

FCCH + SCH + BCCH + CCCH + 3 SDCCH + 3 SACCH + CBCH

Dedicated signaling channels for 3 subscribers

SDCCH Channel with Cell Broadcast Channel

SCBCH

7 SDCCH + 7 SACCH + CBCH

Dedicated signaling channels for 7 subscribers

Table 6: Possible SDCCH+CBCH configurations


s

s This corresponds with the following possible configurations of SDCCH TSs per cell:

Number of TSs for control channels

Case Case1 CBCH Case2

No. of TSs

Timeslot

Channel combination

Database acronym

1 TS

1st TS

1 BCCH + 1 CCCH + 3 SDCCH + 1 CBCH

BCBCH

1st TS

1 BCCH + 1 CCCH

MAINBCCH

7 SDCCH + 7 SACCH + 1 CBCH

SCBCH

1 BCCH + 1 CCCH

MAINBCCH


SCBCH

8 SDCCH + 8 SACCH

SDCCH

2 TS

CBCH

nd

2

TS

1st TS Case3 CBCH

More than 2 TS

nd

2

TS

Further TSs

Table 7: Possible configurations of SDCCH with Cell Broadcast

Seizure of 1 SDCCH sub-channel by CBCH leads to decrease of SDCCH capacity per cell and the subscriber’s capacity per cell in consequence.

5.5

SDCCH in case of Dual Band Standard Cell

In case of Dual Band Standard Cells performed in a more efficient way.

(2)

the SDCCH channel allocation can be

Dual band cells (i.e. two independent cells with different bands covering certain area) with a BCCH layer in both frequency bands have independent pools of SDCCH channels (one per frequency band). This realisation is not optimal in case of congestion on SDCCH in one of frequency bands. In such a situation there is no possibility to use the SDCCH resources from the second (not congested) SDCCH pool. Moreover, in a Dual Band Standard Cell the maximum number of served users can be increased, what is possible thanks to common SDCCH resources for both frequency bands (one SDCCH pool). This approach allows reduction of timeslots required for SDCCH and this leads to increased number of TSs for traffic channels.

2 Dual Band Standard Cell - Realisation of multi-band cells approach with a common BCCH layer. In contrary to the concentric cell approach, a cell radius is assumed to be the same for both frequency bands. It means that both bands shall have well-matching cell borders. Dual Band Standard Cell has only one common BCCH layer and a common cell identity. 28 Planning Guideline: SDCCH dimensioning

s

s 5.6

SDCCH limitations Only one CBCH channel allowed per cell, In case of concentric cells: no SDCCH-SDCCH handover inner complete inner area possible,

complete /

In case of extended cells: no SDCCH-SDCCH handover near far near (single timeslot  double timeslot) possible,

far /

Up to 4 radio timeslots per TRX can be configured as SDCCH/8 (TCHSD) on BTS due to memory availability, There is only one SDCCH/4 channel per cell possible. 5.7

Limitations of channel type TCHSD In case of Dual Band Cells GSM900/1800 the SDCCH/8 and TCHSD used as SDCCH has to be configured in the same BCCH frequency band, The channel configuration changes from TCH (Full Rate or Dual Rate) to TCHSD or vice versa cause a reset of BBSIG

(3)

(for generation 'BTS one') or

CU (for 'BTSplus' family), Only TCHSDs with CHPOOLTYP=TCHPOOL can be used for GPRS traffic, TCHSD creation is possible since BR6.0 release, In case of Concentric Cells the TCHSD type with SDCCH_POOL or TCHSD_POOL is configurable only on Complete Area, In case of Extended Cells the TCHSD type with SDCCH_POOL or TCHSD_POOL is configurable only on Far Area.

3 BBSIG - Channel oriented board in BTS, which is handling Layer 1 functions related to the channel codec and Layer 2 and Layer 3 functions, especially all channel related call control functions. 29 Planning Guideline: SDCCH dimensioning

s

s 6

Signaling events which require SDCCH resources

There are several procedures which require SDCCH resources to be allocated and which are affecting SDCCH load: Mobility Management: •

Location Update (LUP),

•

Periodic Registration,

•

Location Request (LR),

•

IMSI Attach/Detach;

Connection Management: •

Call setup,

•

Short Message Service (SMS),

•

Subscriber

Controlled

Input

(SCI)

for

Supplementary Services Management (SS) •

Unstructured Supplementary Service Data (USSD).

All these events are shortly described below. Seizure times as well as number of events per Busy Hour will be presented in further chapters. 6.1

Call setup

In case a connection has to be established, a channel for signaling has to be allocated. The authentication, ciphering mode initiation and set-up signaling are performed on the SDCCH channel. The estimated time that the SDCCH is occupied with the performance of a call set-up differs slightly between MS originated (MOC) and MS terminated (MTC) calls. The number of other events like LUPs and the SMSs affects the SDCCH load and therefore also the call setup capacity. 6.2

Location Update

Location Update (LUP) procedure is performed after every change of Location Area (LA) of certain Mobile Station (MS) when the MS is in idle mode. This procedure requires an SDCCH which is occupied during the whole LUP procedure. These events will increase SDCCH load in border cells on Location Area in comparison to average inner cell of this LA.


s

s

Figure 10: Location Area scheme and explanation of border cells

SDCCH dimensioning should also reflect LA size because smaller Location Areas mean more Location Updates during movement of MSs between LAs which causes a higher SDCCH load. 6.3

Periodic Registration (Periodic Location Update)

In order to avoid unnecessary paging of Mobile Stations that have not performed any dedicated call or signaling transaction in the last hours, the MSC may set a subscriber to 'detached' after some time without any activity (Implicit Detach procedure (4)). To make sure that an MS is always reachable if it is really attached to the network, a special type of Location Update called Periodic Registration is performed. This procedure is periodically repeated by the MS and confirms its reachability towards the network before it is implicitly set to ‘detached’. Location Updates and Periodic Registrations are treated as the same events from traffic model point of view. 6.4


The transmission of a Short Message Service (SMS) normally takes place on the SDCCH when the affected MS was previously in 'idle' mode (not connected). If TCH is already allocated ('connected mode' or 'busy mode') and an SMS is to be delivered the SMS transmission takes place on the allocated TCH, using the SACCH channel.

4 Implicit Detach - is the action taken by the VLR to mark an MS as detached when there has been no successful contact between the MS and the network for a time determined by the Implicit Detach timer. The value of the Implicit Detach timer is derived from the Periodic Location Updating timer (for more details please refer to chapter 7.2.3). During an established radio contact, the Implicit Detach timer shall be prevented from triggering Implicit Detach. At the release of the radio connection, the Implicit Detach timer shall be reset and restarted. 31 Planning Guideline: SDCCH dimensioning

s

s The time that is required for transmission of an SMS on the SDCCH is the sum of the set-up time for the SMS transmission, the time it takes to transfer the message itself and the time to close the connection. The holding time for the set-up is slightly shorter than the time for a normal call set-up since less signaling is involved. The SDCCH holding time varies depending on the length of the SMS. 6.5

Supplementary Services Management

Supplementary Services like Call Forwarding (CF), Call Barring (CB), Calling Line Identification Restriction (CLIR) etc. are by the GSM/3GPP standard as Supplementary Services for defined GSM/3GPP teleservices and bearerservices. As these Supplementary Services are standardized, their control (activation, deactivation, interrogation etc.) is usually supported by menu options of the mobile phone but can also be controlled by defined phone key sequences (so-called Subscriber Controlled Input (SCI)). The mobile phone in any case recognizes the SCI and the associated Supplementary Service and signals the corresponding Supplementary Service code towards the network within the messages. For this procedure, a dedicated SDCCH connection is required. 6.6

Unstructured Supplementary Service Data

The Unstructured Supplementary Service Data (USSD) mechanism allows the subscriber and the PLMN operator to define own non-standardized Supplementary Service applications which are associated to specific key sequences (e.g. *88*99# SEND). These key sequences are signalled to the MSC in a transparent manner in form of the entered key combination (as opposed to SCI for standardized Supplementary Services, where the MSC indicates the recognized SS type within the embedded messages). USSD transactions can be both subscriberinitiated and network-initiated (MSC, VLR or HLR). The network (network initiated USSD) can at any time send a USSD message towards an MS. This operation may be either a request (asking the MS to provide information) or a notification (requiring no information in the response from the MS). In case of MS initiated USSD a MS can at any time initiate a USSD request to the network. 6.7

IMSI Attach / Detach

The IMSI Attach is performed when the MS is turned on. IMSI Attach is a variant of the Location Updating procedure and usually requires the same holding time as a normal Location Update. The IMSI Detach procedure enables the MS to indicate to the network that it is about to become inactive. This procedure is usually shorter than an IMSI Attach procedure as the Siemens MSC keeps the duration of the Signaling Connection Control Part (SCCP) connection at a minimum time as it immediately closes down the SCCP connection requested by the BSC (via the message CONNECTION REQUEST) via a CONNECTION REFUSED message (even if the contents of the previously received message is accepted and correctly processed). As opposed to that, the SCCP connections for other SDCCH transaction are established according to the SCCP message sequence: CONNECTION REQUEST CONNECTION CONFIRM 32 Planning Guideline: SDCCH dimensioning

s

s signaling message exchange embedded in DT1 messages RELEASE COMPLETE.

RELEASED

For more information concerning message flows please refer to [PMMF]. 6.8

Location Request

Location Requests are messages used to initiate Location Services. Location Services (LCS) are used for different location applications, which may be service provider dependent. The LCS feature tries to locate the target MS in terms of latitude, longitude and optionally altitude. A new network element which is required to determine the position was introduced, which is called Serving Mobile Location Centre (SMLC). The fundamental purpose of the SMLC is to calculate the location of a MS. The SMLC receives location requests via its associated BSCs. It determines the positioning capability of the MS to assist in the position calculation and after all it calculates the final location and returns it in a location response to the requesting BSC. Number of Location Requests per Busy Hour depends on SMLC version and on positioning method. 6.9

Phantom RACH

The BTS Um Layer 1 functions continuously measure the signal on the RACH. Usually, in alive network, there are always signals to be measured on the RACH slot but not all of them are real accesses from Mobile Stations. The BTS Um Layer 1 functions perform a number of checks to distinguish valid RACH accesses from invalid radio noise signals on the RACH. These checks are based, among others, on criteria such as signal level (RSSI – Received Signal Strength Indicator), signal to noise ratio (SNIR – Signal to Noise and Interferer Ratio), soft decision criterion (SOVA - Input Soft decision Value for the decoder), the Convolution Code and the Training Sequence Code. If these checks fail, the signal is regarded. Moreover, the signal level is checked against the level threshold RACHBT (5) (for details please refer to [DB]) and the burst delay is checked against the distance threshold EXCDIST (6) (accesses with levels lower than RACHBT and distance values greater than defined by EXCDIST are discarded). If, despite all these checks, an invalid RACH signal (noise) is recognized as RACH access by mistake, the BTS forwards this putative CHANNEL REQUEST as a CHANNEL REQUIRED message which leads to an SDCCH activation. As no MS will answer to the associated IMMEDIATE ASSIGNMENT message (no ESTABLISH INDICATION will be received), the SDCCH will be released after expiry of a timer.

5 RACHBT (RACH busy threshold) - defines a threshold for the signal level on the RACH. The general purpose of this parameter is to define a minimum level criterion a received RACH signal must fulfil to be regarded as a real RACH access. 6 EXCDIST (Excessive distance) - this parameter specifies the distance limit (between MS and BTS) to be used for call release if the feature 'call release due to excessive distance' is enabled. For details please refer to [DB]. 33 Planning Guideline: SDCCH dimensioning

s

s Moreover, it has to be considered, that the scenario described above (no ESTABLISH INDICATION received after IMMEDIATE ASSIGNMENT) is not necessarily a real 'phantom RACH' in all cases. The sequence of events is the same if either the IMMEDIATE ASSIGNMENT message is not correctly received at the MS (due to radio interface problems in DL), or if the MS does not manage successfully to transmit the SABM message to the BTS after receipt of the IMM ASS message. Both phantom RACHs and the scenarios described above hint to radio interface problems that require analysis of the planning. From SDCCH point of view phantom RACH mean that the signaling load will be higher than planned because of false SDCCH assignments.


s

s 7

SDCCH channel planning and dimensioning

Dimensioning of SDCCH is strongly connected with network capacity and dimensioning of traffic channels (TCHs) because there is subscriber related signaling load which is handled by SDCCH channels. The point is that SDCCH capacity, in terms of number of subscribers, must be higher than TCH capacity to avoid network limitation caused by limited number of SDCCH channels. Prior to dimensioning of SDCCHs, dimensioning of TCHs needs to be done first. The dimensioning process is strongly dependent on the used traffic model. Through this document the Siemens Traffic Model will be used (for more details about the STM please refer to Appendix A: Siemens Traffic Model). In this traffic model values for signaling are specified which are calculated as it is presented in chapter 7.1. Because abovementioned events are SDCCH related (please refer to chapter 6 for definitions and to chapters 7.1 and 7.2 for detailed values), the calculated signaling related values can be treated as SDCCH related. As this document is focused on SDCCH dimensioning ‘SDCCH’ abbreviation will be used instead of ‘signaling’ in order to avoid misunderstanding, as term ‘signaling’ is more general and can trigger improper understanding of described issues. Dimensioning of SDCCH channels is some trade-off between required capacity for TCH and SDCCH. In order to set up a complete voice connection, TCH and SDCCH channels must be available simultaneously (there are some exceptions to this statement; please refer to chapter 4.2, Direct TCH Assignment). Both of them are equally important in call setup but in any case SDCCH channels should be dimensioned for a lower rate of blocking than TCH channels. This can be justified considering the fact that an SDCCH can only be dimensioned in SDCCH/8 units (i.e. 8 SDCCH sub-channels). Thus the loss of a single SDCCH radio timeslot has a bigger impact on the cells capacity to manage the traffic than the loss of s single TCH (however, usually there is no failure of a single TCH but of a TRX - and usually a TRX contains more TCHs than SDCCH timeslots). Moreover, the signaling capacity cannot be limiting factor during dimensioning (for example describing this relation please refer to chapter 7.3). Based on values from the Siemens Traffic Model (please refer to the Siemens Traffic Model description: chapter 9), it is suggested that blocking rate for signaling (SDCCH) shall not be more than 25% of the TCH blocking rate (i.e. 0.5% for SDCCH and 2% for TCH in case of STM). To enable the planning of the BSS part for a given number of subscribers the following parameters must be known: Cell configuration, TCH traffic per subscriber, SDCCH load per subscriber, Maximum blocking rate of TCH, Maximum blocking rate of SDCCH, 35 Planning Guideline: SDCCH dimensioning

s

s FR/HR ratio, if applicable. The aim is to find the optimal share of available resources between traffic channels (TCHs) and signaling channels (we are focused on SDCCHs, which are conveyed together with other associated control channels; for more details about possible channel configuration please refer to chapter 5.3) with respect to optimum subscriber capacity (number of subscribers that can be served by the system). As stated in the beginning of this chapter, the subscriber capacity of the SDCCH channels (i.e. subSDCCH) shall not be lower than subscriber capacity of the TCHs (i.e. subTCH): subSDCCH ≥ subTCH Where: subSDCCH - Subscriber capacity of SDCCH channels (= number of subscribers that can be served by SDCCH channels of the system), subTCH - Subscriber capacity of TCHs (= number of subscribers that can be served by all TCHs of the system). Both these values depend on the blocking probabilities for SDCCHs and TCHs, respectively. To determine the subscriber capacity for SDCCH and TCH (i.e. the maximum number of subscribers the cell can handle, also called 'SDCCH capacity' and 'TCH capacity' in the following chapters) the following calculations have to be done by means of Erlang B formula (fErlangB):

⎢ cap SDCCH ⎥ ⎢ f ErlangB (# SDCCHs; BSDCCH ) ⎥ subSDCCH = ⎢ ⎥=⎢ ⎥ load sub , SDCCH ⎣⎢ load sub , SDCCH ⎦⎥ ⎢⎣ ⎦⎥ ⎢ capTCH ⎥ ⎢ f ErlangB (# TCHs; BTCH ) ⎥ subTCH = ⎢ ⎥=⎢ ⎥ load sub, TCH ⎣⎢ load sub , TCH ⎦⎥ ⎢⎣ ⎦⎥

Where the results of these calculations are in numbers of users, and moreover: capSDCCH – capacity of SDCCH channels per cell [Erl], capTCH – capacity of TCH channels per cell [Erl], loadsub, SDCCH – SDCCH load per subscriber [Erl], loadsub, TCH - TCH traffic per subscriber [Erl], #SDCCH – Number of SDCCHs, #TCH – Number of TCHs, BSDCCH - Maximum blocking rate of SDCCH, BTCH - Maximum blocking rate of TCH. 36 Planning Guideline: SDCCH dimensioning

s

s The denominators loadsub, SDCCH and loadsub, TCH are values of SDCCH and TCH load per subscriber respectively. Both these values are calculated in chapter 7.1. Blocking rate value of SDCCH channels (i.e. BSDCCH) in this document will have value of blocking rate for signaling (i.e. BSignaling) taken from Siemens Traffic Model (for details please refer to chapter 9). The subscriber related SDCCH load (loadsub, SDCCH; in the Siemens Traffic Model this value is 4 mErl) used in equations above is borne by the SDCCH channels. This traffic can be calculated by the following formula: loadsub, SDCCH = (NCA/sub, BH tcall setup + NLUP tLUP + NSMS tSMS + NLR tLR) [Erl] Where: NCA/sub, BH - Number of Call Attempts per subscriber per Busy Hour, tcall setup - Call setup time: the time an SDCCH is seized by an call setup, NLUP - Number of location updates per subscriber and BH, tLUP - Location update time, NSMS - Number of SMS messages per subscriber and BH, tSMS - SMS time, NLR - Number of Location Requests per subscriber and BH, tLR - Location Request time.

This equation can be extended when other events which require some SDCCH capacity occur (e.g. SS/USSD). In such a case respective term (NSS/USSD tSS/USSD) must be added, assuming number of SS/USSD messages per subscriber and BH (NSS/USSD) according to relevant Traffic Model and SDCCH seizure time per SS/USSD (tSS/USSD) event: loadsub, SDCCH = (NCA/sub,BH tcall setup + NLUP tLUP + NSMS tSMS + NLR tLR + NSS/USSD tSS/USSD) The used time figures generally depend on several factors. As an example tcall setup strongly depends on used core features like authentication, TMSI reallocation and IMEI check and as well on mechanisms like "late TCH assignment" (CS4 message flow redesign with respect to R4 core architecture) which also affects the TCH holding time.


s

s 7.1

SDCCH seizure Times

Assuming that the Siemens Traffic Model applies, a value of 4 mErl of SDCCH load per subscriber (loadsub, SDCCH) results from the inputs presented below. These values should be treated as “rough guess” values and, as it was stated in the previous chapter, all the time figures must be verified case by case. After the dimensioning process these values should be verified by measurements performed in the network, in order to check the correctness of values used during the dimensioning process. Event

Symbol

Description

Unit

CA

tcall setup

LUP

tLUP

Periodic Registration is assumed to require the same time as normal Location Update.

SMS

tSMS


LR

tLR

Location Request

USSD

tUSSD

Call Attempt.

Value 3

Time for MOC/MTC setup signaling (Call setup time) Location Update time.

5 second 6 ≈ 1.3 (7)

Unstructured Supplementary Services Data

3

Table 8: Seizure times of events on SDCCH channel

The abovementioned value of 4 mErl of SDCCH load per subscriber is calculated as follows: loadsub, SDCCH =

NCA/sub, BH ⋅ t call setup + N LUP ⋅ t LUP + N SMS ⋅ t SMS 3600

=

1 ⋅ 3 + 2 ⋅ 5 + 0.2 ⋅ 6 14.2 = ≅ 4 mErl 3600 3600

For number of events generated per subscriber please refer to next chapter. In the similar way is calculated voice traffic per subscriber per BH: load sub , TCH =

(N MOC + N MTC ) ⋅ Tmh (0.6 + 0.4) ⋅ 90 90 = = = 25 mErl 3600 3600 3600

Where: NMOC - Mobile Originating Call attempts per subscriber and BH, NMTC - Mobile Terminating Call attempts per subscriber and BH, Tmh - Mean holding Time.

7 This value of SDCCH seizure time corresponds to CITA positioning method. 38 Planning Guideline: SDCCH dimensioning

s

s 7.2

SDCCH load generated by subscriber

Assuming that the Siemens Traffic Model applies, a value of 4 mErl of signaling load per subscriber (loadsub, SDCCH) results from the input values presented below. All these values are numbers of events per Busy Hour. 7.2.1 Call attempt Number of call attempts (CA) that can be handled by one TCH in the BH: NCA/sub, BH = 1 7.2.2 Location Update Location Update (LUP) procedures amount is strongly dependent on the cell location inside the Location Area (LA) because the number of updates is higher on the border of LA than inside of it. Moreover the number of LUPs on the LA border cell depends on traffic load. NLUP = 2. 7.2.3 Periodic Registration (Periodic Location Update) If Periodic Registration is used, the time between these registrations depend on operator choice. If so, the SDCCH load caused by Periodic Registration varies depending on the setting of the Periodic Location Update timer, which is managed by the BSC database parameter T3212 (8). The expected number of periodic LUP transactions can be estimated by dividing 60 minutes (i.e. duration of the BH) by periodic LUP timer value which is multiplied by 6. Assuming the default value of T3212 = 6 = 36min (with granularity of decihour = 6 min.), the average number of periodic LUPs per subscriber and BH can be estimated as follows: N P − LUP =

60 min 60 min 60 min = = = 1,67 T 3212 value ⋅ 6 min 6 ⋅ 6 min 36 min

Thus a qualified guess for the expected number of periodic LUPs per subscriber and BH is: NP-LUP = 1,5. If T3212 is set to 60 minutes (T3212 = 10), the resulting value is: NP-LUP = 1.

8 T3212 - Timer for periodic Location Update (please refer to chapter 6.3 for more information about periodic LUP). The periodic LUP procedure is controlled by the timer T3212 in the MS. This timer is reset to 0 and started when a signaling activity has taken place on the radio path (e.g. Location update, MOC, IMSI Attach). When the MS is powered down the current value of T3212 is kept in memory. When the MS is powered up the timer starts running from the value thus contained in memory. On expiry the MS initiates a Location Updating. 39 Planning Guideline: SDCCH dimensioning

s

s 7.2.4 SMS The number of SMS transmissions strongly depends on the subscriber’s behavior and network specific conditions, such as the operator’s habits to transmit terminating SMS messages to registered subscribers, either distributed or in 'bursts'. NSMS = 0.2. 7.2.5 Location Request The default value of Location Requests per hour is zero (Location Services not considered; this value shall be adapted according to customers requirements). NLR = 0 When LCS is enabled, typically a value of around NLR = 0.092 shall be taken into account (please refer to chapter 9: Appendix A: Siemens Traffic Model). NLR = 0.092 Number of Location Requests per Busy Hour depends on SMLC version and on positioning method. 7.2.6 IMSI Attach/Detach Based on information from the Siemens Traffic Model the number of IMSI Attach/Detach events is assumed to be zero, because these events are taken into account within Location Update events amount. 7.3

Required amount of SDCCH resources per cell

The tables below show all the information needed to calculate required number of SDCCH resources for certain number of TRXs per cell. The SDCCH load depends on amount of load per subscriber, so number of TCHs must be considered. Based on the already presented information (description of the dimensioning process in chapter 7) sum of #TCH/Fs and #TSs for signaling (both are columns in the table 9) is total number of timeslots (#TSs) for certain number of TRXs (#TRXs). Moreover both these values (i.e. #TCH/Fs and #TSs for signaling) depend on each other and are obtained with respect to flow chart presented on figure 12, which shows principles of iterative calculation of required number of SDCCH channels where number of TRXs is an input value. The calculation presented in the table below assumes values from Siemens Traffic Model: loadsub, TCH = 25 mErl, loadsub, SDCCH = 4 mErl, BSDCCH = 0.5%, BTCH = 2%.


s

s All the 4 input values mentioned above may be different for other traffic models. Thus the table below is only an example to show the principle way of computation. The traffic value (in Erl) is always related to calls, no matter whether FR or HR. E.g. 26 Erl for HR means that 26 HR trunks can be served utilizing only 13 TSs. Full Rate subscriber (FR)

# TCH/Fs

# TSs

# TRXs

TCH channels

Signaling channels BCCH

TCH capacity capTCH

#subscribers (TCH) (subTCH)

#TSs

+

for signaling

BCCH +

8SDCCH

CCCH +

CCCH

8SACCH

[Erl]

SDCCH Capacity total

+

capSDCCH

#SDCCH

#subscribers (SDCCH) (subSDCCH)

[Erl]

4SDCCH

1

8

7

2.9354

117

2

16

14

8.2

328

3

24

22

14.895

595

4

32

29

21.039

841

5

40

37

28.253

1130

6

48

45

35.607

1424

7

56

53

43.06

1722

8

64

61

50.587

2023

9

72

68

57.225

2289

10

80

76

64.856

2594

11

88

84

72.528

2901

12

96

92

80.235

3209

1

1

0

0

4

0.7011

175

2

0

1

1

8

2.729

682

3

0

1

2

16

8.099

2024

4

0

1

3

24

14.203

3550

Table 9: Calculation of #TCH and #SDCCH depending on #TRX for 100% Full Rate

The value of TCH capacity (capTCH) as well as SDCCH capacity (capSDCCH) is calculated using Erlang B formula, e.g. for 1 TRX: ⎢ capSDCCH ⎥ ⎢ f ErlangB (# SDCCHs; BSDCCH ) ⎥ ⎢ f ErlangB (4; 0.5% ) ⎥ ⎢ 0.7011 Erl ⎥ subSDCCH = ⎢ ⎥=⎢ ⎥=⎢ ⎥ = ⎢ 4 mErl ⎥ = 175 load sub , SDCCH 4 mErl ⎦ ⎣ ⎦ ⎣⎢ load sub , SDCCH ⎦⎥ ⎣⎢ ⎦⎥ ⎣ ⎢ capTCH ⎥ ⎢ f ErlangB (# TCHs; BTCH )⎥ ⎢ f ErlangB (7; 2% ) ⎥ ⎢ 2.9354 ⎥ subTCH = ⎢ ⎥=⎢ ⎥=⎢ ⎥=⎢ ⎥ = 117 load sub , TCH ⎢⎣ load sub , TCH ⎥⎦ ⎢⎣ ⎥⎦ ⎣ 25mErl ⎦ ⎣ 25mErl ⎦ For detailed description of above equations please refer to chapter 7.

As can be seen in the table above, 1 TS for signaling is only applicable in case of one TRX per cell, because the amount of subscribers for two TRXs 41 Planning Guideline: SDCCH dimensioning

s

s (i.e. 328 subscribers) is higher than signaling capacity of 1 TS (i.e. 175 subscribers). This leads to the conclusion: 1 TRX per cell:

1 signaling TS per cell,

> 1 TRX per cell:

> 1 signaling TS per cell.

The flow chart presented below can be used in order to calculate required number of TRXs for specified amount of TCH traffic. This flow chart corresponds to values from Table 9 (FR trunks). The table above, as well as the flow chart, assumes the Siemens Traffic Model. The operator must be aware that different traffic models (or just a modification of STM) may cause values different from those presented in this document and moreover presented flow charts may be not optimal anymore.


s

s TCH traffic TCH TRAFFIC [Erl]

INPUT

TCH TRUNKS = 1

⎢ TCH TRAFFIC ⎥ subTCH = ⎢ ⎥ ⎣ 25 mErl ⎦

Find number of traffic trunks required to convey given TCH traffic.

capTCH [Erl] = f ErlangB (TCH TRUNKS; 2 %) TCH TRUNKS = TCH TRUNKS + 1

capTCH ≥ TCH TRAFFIC

No

Yes

SDCCH SUB-CHANNELS = 1 SDCCH LOAD [Erl] = subTCH * 4 mErl

Find number of signaling subchannels required to convey signaling caused by users.

cap SDCCH [Erl] = f ErlangB (SDCCH SUB-CHANNELS; 0.5 %) SDCCH SUB-CHANNELS = SDCCH SUB-CHANNELS + 1

cap SDCCH ≥ SDCCH LOAD

Decide wheatear this is combined or uncombined configuration. Using Siemens Traffic Model combined configuration of signaling channels is applicable only for configuration with 100% FR and one TRX (per cell).

Yes

SDCCH SUB −CHANNELS ≤ 4

No

No

BCCH = 0

Calculate number of TRXs.

BCCH = 1 Combined configuration SDCCH/4

Uncombined configuration SDCCH/8

⎡ SDCCH SUB−CHANNELS ⎤ ⎥ + TCH TRUNKS + BCCH 8 ⎥

∑ TS = ⎢⎢

⎡ ∑ TS ⎤ ∑ TRX = ⎢⎢ 8 ⎥⎥

RESULT

Figure 11: Flow chart for calculation of #TRXs for specified TCH load (Full Rate)


s

s In order to use this flow chart to Half Rate trunks, the calculation of the number of TSs (in the last step of this flow chart) should look as follows: ⎡ SDCCH SUB −CHANNELS 8

∑ TS = ⎢⎢

⎤ ⎡ TCH TRUNKS ⎥+⎢ 2 ⎥ ⎢

⎤ ⎥ + BCCH ⎥

After this correction, the values from table below can be found. Half Rate subscriber (HR)

# TCH/Hs

# TSs

# TRXs

TCH channels

Signaling channels

TCH capacity capTCH

BCCH #subscribers (TCH) (subTCH)

# TSs

+

for signaling

BCCH +

8SDCCH

CCCH +

CCCH

8SACCH

[Erl]

SDCCH Capacity total

+

capSDCCH

#SDCCH

#subscribers (SDCCH) (subSDCCH)

[Erl]

4SDCCH

1

8

12

6.614

264

2

16

26

18.382

735

3

24

42

32.836

1313

4

32

58

47.758

1910

5

40

72

61.036

2441

6

48

88

76.378

3055

7

56

102

89.91

3596

8

64

118

105.468

4218

9

72

134

121.104

4844

10

80

148

134.837

5393

11

88

164

150.581

6023

12

96

180

166.37

6654

2

0

1

1

8

2.722

682

3

0

1

2

16

8.099

2024

4

0

1

3

24

14.204

3551

5

0

1

4

32

20.677

5169

6

0

1

5

40

27.381

6845

Table 10: Calculation of #TCH and #SDCCH depending on #TRX for 100% Half Rate

According to equation: subSDCCH ≥ subTCH all the time the number of subscribers on SDCCH must be greater than the number of subscribers on TCHs. The number of timeslots per cell differs depending on the trunk type: 44 Planning Guideline: SDCCH dimensioning

s

s In case Full Rate: # TS = # TS SDCCH + # TCH / F

⎡ # TCH / F ⎤ In case Half Rate: # TS = # TS SDCCH + ⎢ ⎥⎥ 2 ⎢ As can be seen above, for a given #TRXs the #TCH/Fs is almost half of #TCH/Hs. One TS for CCCH is considered regardless of the cell configuration. The number of resources needed for the CCCHs must be calculated separately. The dimensioning of CCCHs is not in the scope of this document. The picture below depicts a flow chart that presents how the number of radio timeslots for TCH and for SDCCH can be determined. This flow chart was prepared for 100% Full Rate traffic. In order to use it in case of Half Rate traffic the only difference is to change equation to calculate number of trunks:

TCH TRUNKS = TCH TS ⋅ 2 Additional assumption for HR traffic calculations is that cells are equally loaded with HR mobiles (the same HR penetration in all cells).


s

s #TRX

INPUT

#TS = #TRX * 8

#TRX = 1 & Full Rate traffic

Configuration with one TRX and 100 % Full Rate traffic Yes

No SDCCH SUB-CHANNELS = 8

SDCCH SUB-CHANNELS = 4 (SDCCH/4)

(SDCCH/8)

⎢ SDCCH SUB−CHANNELS ⎥ TS TCH = # TS − ⎢ ⎥ − 1 (BCCH ) 8 ⎦ ⎣ TCH TRUNKS = TS TCH SDCCH SUB-CHANNELS = SDCCH SUB-CHANNELS + 8

cap SDCCH [Erl] = f ErlangB (SDCCH SUB-CHANNELS; 0.5 %) cap TCH [Erl] = f ErlangB (TCH TRUNKS; 2 %)

subTCH =

capTCH 25 mErl

subSDCCH =

capSDCCH 4 mErl subSDCCH ≥ subTCH

No Yes

⎢ SDCCH SUB−CHANNELS ⎥ TS TCH =# TS − ⎢ ⎥ − 1 (BCCH ) 8 ⎣ ⎦ TCH TRUNKS = TS TCH

RESULT

⎢ SDCCH SUB−CHANNELS ⎥ SDCCHTS = ⎢ ⎥ 8 ⎣ ⎦

Figure 12: Flow chart for calculation of TSs for traffic and signaling (Full Rate)


s

s 7.3.1 Mixture of HR and FR In contrast to the previously described cases there is usually a mixture of FR and HR in the TCH utilization. Half Rate will increase the number of TCH channels and therefore more signaling will be required what leads to SDCCH re-dimensioning. Of course also in these cases the equation subSDCCH ≥ subTCH must be fulfilled. Examples of dimensioning in case of FR/HR mixture are presented in chapter 8: Dimensioning examples, section 8.1: Example of mixture of FR and HR. Depending on the FR/HR ratio the following table defines the optimum number of TSs to be spent for TCH. Calculations were performed for values of traffic and blocking taken from Siemens TM: FR percentage # TRX

0

10

20

30

40

50

60

70

80

90

100

1

6

6

6

6

6

6

7

7

7

7

7

2

13

13

13

14

14

14

14

14

14

14

14

3

21

21

21

21

21

21

21

21

21

22

22

4

29

29

29

29

29

29

29

29

29

29

29

5

36

36

36

36

37

37

37

37

37

37

37

6

44

44

44

44

44

44

44

45

45

45

45

7

51

52

52

52

52

52

52

52

52

53

53

8

59

59

59

59

60

60

60

60

60

60

61

9

67

67

67

67

67

67

68

68

68

68

68

10

74

75

75

75

75

75

75

76

76

76

76

11

82

82

82

83

83

83

83

83

84

84

84

12

90

90

90

90

90

91

91

91

91

91

92

Table 11: Number of TCH TSs (TSTCH) in case of HR/FR mixture

The table above was computed by means of the Erlang B formula. The numbers of TSs to be used for traffic are chosen in such a way that, considering the number of TSs remaining for signaling, the maximum number of subscribers can be served. Detailed calculation example can be found in chapter 8.1.2.


s

s The table below gives the figures for the number of signaling TSs: FR percentage # TRX

0

10

20

30

40

50

60

70

80

90

100

1

2

2

2

2

2

2

1

1

1

1

1

2

3

3

3

2

2

2

2

2

2

2

2

3

3

3

3

3

3

3

3

3

3

2

2

4

3

3

3

3

3

3

3

3

3

3

3

5

4

4

4

4

3

3

3

3

3

3

3

6

4

4

4

4

4

4

4

3

3

3

3

7

5

4

4

4

4

4

4

4

4

3

3

8

5

5

5

5

4

4

4

4

4

4

3

9

5

5

5

5

5

5

4

4

4

4

4

10

6

5

5

5

5

5

5

4

4

4

4

11

6

6

6

5

5

5

5

5

4

4

4

12

6

6

6

6

6

5

5

5

5

5

4

Table 12: Number of signaling TSs (TSsign) in case of mixture of HR and FR

Adding values from both tables from the same cell should give in total the number of TS for certain number of TRXs: #TRX * 8, e.g.: #TRX = 8, FR percentage = 60%. For such an input there is: 60 TSs for TCHs (table 11), 4 TSs for signaling (table 12), Total number of TS is: 60 + 4 = 64 TSs. In the table 13 values of the number of trunks for certain configuration are presented. These values are calculated based on values from table 11 in the way presented in the following example: #TRX = 11, FR percentage = 30%. For such an input there is (based on the table 11) 83 TSs for TCHs. This value has to be multiplied by FR percentage in order to calculate Full Rate TSs:

TS FR = ⎡TS TCH ⋅ FR% ⎤ = ⎡83 TS ⋅ 30%⎤ = ⎡24.9 TS ⎤ = 25 TS TS HR = TS TCH − TS FR = 83 − 25 = 58 TS 48 Planning Guideline: SDCCH dimensioning

s

s Based on the number of timeslots for certain rate, the number of trunks can be calculated:

FRTRUNKS = TS FR = 25 HRTRUNKS = TS HR ⋅ 2 = 58 ⋅ 2 = 116 Total number of trunks is the sum of above values:

TCH TRUNKS = FRTRUNKS + HRTRUNKS = 25 + 116 = 141 The value calculated above value can be found in the table 13. FR percentage # TRX

0

10

20

30

40

50

60

70

80

90

100

1

12

11

10

10

9

9

9

9

8

7

7

2

26

24

23

23

22

21

19

18

16

15

14

3

42

39

37

35

33

31

29

27

25

24

22

4

58

55

52

49

46

43

40

37

34

31

29

5

72

68

64

61

59

55

51

48

44

40

37

6

88

83

79

74

70

66

61

58

54

49

45

7

102

98

93

88

83

78

72

67

62

58

53

8

118

112

106

100

96

90

84

78

72

66

61

9

134

127

120

113

107

100

95

88

81

74

68

10

148

142

135

127

120

112

105

98

91

83

76

11

164

155

147

141

132

124

116

107

100

92

84

12

180

171

162

153

144

136

127

118

109

100

92

Table 13: Number of trunks (HR and FR)

Based on the tables above the following table defines the total traffic that can be conveyed on the TCHs. Values in the table 14 were calculated in terms of Erlang B formula, witch blocking probability of 2 % (Siemens Traffic Model) and for number of trunks taken from the table 13.


s

s FR percentage # TRX

0

10

20

30

40

50

60

70

80

90

100

1

6.61

5.84

5.08

5.08

4.34

4.34

4.34

4.34

3.63

2.93

2.93

2

18.38

16.63

15.76

15.76

14.90

14.04

12.33

11.49

9.83

9.01

8.20

3

32.83

30.08

28.25

26.43

24.63

22.83

21.04

19.26

17.50

16.63

14.90

4

47.76

44.94

42.12

39.32

36.53

33.76

31.00

28.25

25.53

22.83

21.04

5

61.04

57.23

53.43

50.59

48.70

44.94

41.19

38.39

34.68

31.00

28.25

6

76.38

71.57

67.73

62.94

59.13

55.32

50.59

47.76

43.98

39.32

35.60

7

89.91

86.03

81.20

76.38

71.57

66.77

61.04

56.27

51.53

47.76

43.06

8

105.47

99.62

93.79

87.97

84.10

78.31

72.53

66.77

61.04

55.32

50.59

9

121.10

114.25

107.42

100.60

94.76

87.97

83.13

76.38

69.65

62.94

57.23

10

134.84

128.95

122.08

114.25

107.42

99.62

92.82

86.03

79.27

71.57

64.86

11

150.58

141.71

133.86

127.97

119.15

111.32

103.52

94.76

87.97

80.24

72.53

12

166.37

157.48

148.61

139.75

130.91

123.06

114.25

105.47

96.71

87.97

80.24

Table 14: Traffic capacity [Erl]


s

s 8

Dimensioning examples

8.1

Example of mixture of FR and HR 8.1.1 Example using values from HR/FR tables

Assumption: A cell is equipped with 2 TRXs which 10 % of FR connections. This configuration (after comparison of signaling and traffic capacities and iterative recalculations) allows 13 TS for TCH and 3 TSs must be allocated for signaling. In case of 10 % of FR connections there would be 1.3 FR subscribers what require roundup and results with 2 FR users, and 11 HR timeslots. The total number of TCHs in this case is 24 (2 TCH/F trunks + 22 TCH/H trunks). TCH capacity is then calculated for 22 TCHs using Erlang B formula and certain blocking rate. Below an example of mixture of HR and FR is shown with detailed calculation performed step by step. Input values are: Full Rate percentage - FR% = 10 %, #TRXs = 2. Values

Remark

1

Number of TSs available for traffic (TSTCH)

13

2

Number of FR trunks (FRTRUNKS)

2 TSs – 2 trunks

3

Number of HR trunks (HRTRUNKS)

11 TSs – 22 trunks

4

Total number of trunks (TCHtrunks)

24

4

total offered traffic (capTCH)

16.63

5

# subscribers according to TCH (subTCH)

665

6

Number of TSs available for signaling (TSsign)

3

7

SDCCH capacity (capSDCCH)

8.1

8

# subscribers according to SDCCH (subTCH)

2025

subTCH = capSDCCH / 4 mErl

9

# subscribers according to TCH and SDCCH

665

min(subTCH, subSDCCH)

According to table 11. TSFR = TSTCH * FR% = 13 TSs * 10 % = 1.3 2 TSs for FR TSHR = TSTCH – TSFR = 13 TSs - 2 TSs for FR = 11 TSs for HR TCHtrunks = TCHtrunks + TCHtrunks = 22 HR trunks + 2 FR trunks = 24 trunks Calculated by Erlang B formula (24 trunks; 2% blocking rate) subTCH = capTCH / 25 mErl TSsign = 8 * #TRXs – TSTCH = 16 – 13 = 3 3 TSs for signaling means 1 TS for BCCH and 2 TSs for SDCCH (16 SDCCH/8 sub-channels) Calculated by Erlang B formula (16 sub-channels; 0.5% blocking rate)

Table 15: Calculation example 51 Planning Guideline: SDCCH dimensioning

s

s 8.1.2 Complete calculation (without HR/FR tables) Assumptions: TRXs:

#TRX = 12

Full Rate percentage:

FR% = 40%

Calculation: Step 1 1. Total number of TSs:

#TS = 96

TS =# TRX ⋅ 8 = 12 ⋅ 8 = 96 2. TCH trunks: 100% FR: 100% HR: 3. TCH TSs for 100% FR:

FRTRUNKS = 92

(According to Table 13)

HRTRUNKS = 180

(According to Table 13)

TSTCH 100% FR = 92

TS TCH 100% FR = FRTRUNKS = 92 = TS TCH temp

4. TCH TSs for 100% HR:

TS TCH 100% HR =

TSTCH 100% HR = 90

HRTRUNKS 180 = = 90 2 2

5. Signaling TSs for 100% FR: TSsign 100%FR = 4

(According to table Table 12)

6. Signaling TSs for 100% HR: TSsign 100%HR = 6

(According to table Table 12)

The number of TCH TSs in case of FR/HR mixture will be within the range (90 - 92). To evaluate these value iterative calculations needs to be done. Starting from the higher value (in this example 92 TSs), the calculation will be proceeded in order to find the optimal ratio between TCH and SDCCH channels providing the maximum number of subscribers.


s

s 7. TCH TSs for mixture: FR:

TSTCH MIX FR = 37

TS TCH MIX FR = ⎡TS TCH temp ⋅ FR% ⎤ = ⎡92 ⋅ 0.4⎤ = ⎡36.8⎤ = 37 8. TCH TSs for mixture: HR:

TS TCH

MIX HR

= TS TCH

temp

− TS TCH

TSTCH MIX HR = 55 MIX FR

9. TCH trunks:

= 92 − 37 = 55

TCHTRUNKS = 147

TCH TRUNKS = TS TCH MIX FR + TS TCH MIX HR ⋅ 2 = 37 + 55 ⋅ 2 = 147

10. Signaling TSs:

TSsign = 4

TS sin g = TS − TS TCH temp = 96 − 92 = 4

11. SDCCH sub-channels:

[

SDCCHSUB-CHANNELS = 24

]

SDCCH SUB −CHANNELS = TS sign − 1( BCCH ) ⋅ 8 = (4 − 1) ⋅ 8 = 24 12. SDCCH capacity:

capSDCCH = 14.2 [Erl]

cap SDCCH = f ErlangB ( SDCCH SUB −CHANNELS ; 0.5%) = 14.2 [ Erl ] 13. SDCCH subscribers:

⎢ cap SDCCH subSDCCH = ⎢ ⎣ 4 mErl

subSDCCH = 3550

⎥ ⎢ 14.2 ⎥ ⎥ = ⎢ 0.004 ⎥ = 3550 ⎦ ⎦ ⎣

14. TCH capacity:

capTCH = 133.86 [Erl]

capTCH = f ErlangB (TCH TRUNKS ; 2%) = f ErlangB (147; 2%) = 133.86 [ Erl ]

15. TCH subscribers:

subTCH = 5354

⎢ capTCH ⎥ ⎢133.86 ⎥ subTCH = ⎢ ⎥=⎢ ⎥ = 5354 ⎣ 25 mErl ⎦ ⎣ 0.025 ⎦ The calculated number of TCH subscribers is greater than that of SDCCH subscribers (i.e. 5354 vs. 3550) so a recalculation must be done for a changed number of SDCCH sub-channels (increase number of SDCCH TSs which leads to reduction of traffic TSs). 53 Planning Guideline: SDCCH dimensioning

s

s Step 2 Starting from point 7 the results are recalculated for:

TS TCH temp = TS TCH temp − 1 = 92 − 1 = 91

7. TCH TSs for mixture: FR:

TSTCH MIX FR = 37


TSTCH MIX HR = 54

TS TCH MIX HR = TS TCH temp − TS TCH MIX FR = 91 − 37 = 54

9. TCH trunks:

TCHTRUNKS = 145


10. Signaling TSs:

TSsign = 5



[


]





subSDCCH = 5170

⎥ ⎢ 20.68 ⎥ ⎥ = ⎢ 0.004 ⎥ = 5170 ⎦ ⎦ ⎣

14. TCH capacity:


capTCH = f ErlangB (TCH TRUNKS ; 2%) = f ErlangB (145; 2%) = 131.89 [ Erl ]


s

s 15. TCH subscribers:

subTCH = 5275

⎢ capTCH ⎥ ⎢131.89 ⎥ subTCH = ⎢ ⎥=⎢ ⎥ = 5275 ⎣ 25 mErl ⎦ ⎣ 0.025 ⎦ SDCCH capacity is still smaller than TCH capacity (5170 SDCCH users < 5275 TCH subscribers) so another iteration must be performed. Number of SDCCH timeslots is increased again by 1 TS. Step 3

TS TCH temp = TS TCH temp − 1 = 91 − 1 = 90

7. TCH TSs for mixture: FR:

TSTCH MIX FR = 36


TSTCH MIX HR = 54

TS TCH MIX HR = TS TCH temp − TS TCH MIX FR = 90 − 36 = 54

9. TCH trunks:

TCHTRUNKS = 144


10. Signaling TSs:

TSsign = 6



[


]





subSDCCH = 6845

⎥ ⎢ 27.38 ⎥ ⎥ = ⎢ 0.004 ⎥ = 6845 ⎦ ⎦ ⎣ 55


s

s 14. TCH capacity:


capTCH = f ErlangB (TCH TRUNKS ; 2%) = f ErlangB (144; 2%) = 130.91[ Erl ]

15. TCH subscribers:

subTCH = 5236

⎢ capTCH ⎥ ⎢130.91⎥ subTCH = ⎢ ⎥=⎢ ⎥ = 5236 ⎣ 25 mErl ⎦ ⎣ 0.025 ⎦ Finally the SDCCH capacity is not smaller than the TCH capacity (6845 SDCCH subscribers and 5236 TCH subscribers) and the calculation is finished. Based on the presented calculation, also the number of TCHSD channels in TCHSD_POOL can be derived. For recommendation describing suggested approach of TCHSD channels creation for TCHSD_POOL, please refer to chapter 4.4.3. For more information about the Smooth Channel Modification feature, please refer to chapter 4.4.

8.2

Dimensioning example of SMS Cell Broadcast implementation

The following picture shows a 4/4/3 BTSE configuration (100% Full Rate and 100% Half Rate): 4 TRX 3 TRX 4 TRX

Figure 13: 4/4/3 site configuration

There are two cells with 4 TRXs (NTRX, cell = 4) and one cell with 3 TRXs. In case of HR the number of trunks per TRX is doubled compared to FR and the calculation of TCH channels considers this fact.


s

s Full Rate

Half Rate

#cells

3

#TRXs

4/4/3 NTRX, cell* 8 - TSsign =

NTRX, cell *16 - TSsign * 2 =

3*8-2=

3 * 16 – 3 * 2 =

22

42

NTRX, cell* 8 - TSsign =

NTRX, cell*16 – TSsign * 2 =

4*8-3=

4 * 16 – 3 * 2 =

29

58

3 TRX

14.895 Erl

32.836 Erl

4 TRX

21.039 Erl

47.757 Erl

3 TRX

14.895 Erl = 595 25 mErl

32.836 Erl = 1313 25 mErl

4 TRX

21.039 Erl = 841 25 mErl

47.757 Erl = 1910 25 mErl

3 TRX #TCHs 4 TRX

Traffic

#subscribers

Table 16: Calculation of values for FR and HR

The number of TCHs is calculated as the number of TRXs multiplied by the number of trunks per one carrier (8 in case of FR and 16 in case of HR) and this number is reduced by number of signaling TSs. The number of signaling channels varies by the number of TRXs for FR and HR separately. The number of signaling channels for a certain number of TRXs can be found in Table 9 (FR) and Table 10 (HR). For the calculated number of TCHs the amount of traffic is calculated based on the Erlang B formula. Considering the Siemens TM, the number of subscribers per cell is calculated as traffic divided by loadsub, TCH = 25 mErl. The table below shows the impact of SMS Cell Broadcast activation on the subscriber’s capacity of cell. In the example below the Siemens Traffic Model is considered.


s

s Full Rate (FR) per cell:

SMS-CB disabled

SMS-CB enabled

# TRXs

NTRX, cell

3

4

3

4

# TCHs

TCH

22

29

21

29

# TSs for signaling

TSsign

2

3

3

3

# SDCCHs

SDCCH

8

16

15 = 16 – 1

15 = 16 – 1

TCH capacity

capTCH

14.895 Erl

21.039 Erl

14.036 Erl

21.039 Erl

SDCCH capacity

capSDCCH

2.729 Erl

8.099 Erl

7.3755 Erl

7.3755 Erl

subscriber capacity (TCH)

subTCH

595

841

561

841

subscriber capacity (SDCCH)

subSDCCH

682

2024

1843

1843

Table 17: Impact of SMS Cell Broadcast on cell capacity

Results for cell with 3 TRXs: In case of 3 TRXs the required number of TSs for signaling is 2 (Case 2; please refer to chapter 5.3 and 5.4). As a CBCH requires resources on one of available TSs there would be reduction of available SDCCH sub-channels (from 8 to 7 in this case). 2 TSs for signaling are no longer sufficient when Cell Broadcast is enabled. They correspond with 7 SDCCH sub-channels available and a subscriber’s capacity of 539 (instead of 8 SDCCHs and 682 subscribers for case without Cell Broadcast).

W/o CBCH

2 TS

1st TS 2

nd

1 BCCH + 1 CCCH

TS

8 SDCCH + 8 SACCH

st

With CBCH

2 TS

1 TS

1 BCCH + 1 CCCH

2nd TS


Table 18: Configuration of control channels in cell with 3 TRXs

Due to the fact that the subscribers capacity of TCH channels remains the same (and thus exceeds SDCCH capacity of the cell) another TS must be assigned for SDCCH purposes. The number of SDCCH channels must be increased at the cost of TCH channels. This will lead to a configuration with 3 signaling TSs and 21 TCHs (instead of 22 TCHs). Three available TSs for signaling leads to SDCCH with CBCH configuration Case 3 (please refer to chapter 5.3 and 5.4):


s

s 1st TS Case3 CBCH

More than 2 TS

2

nd

1 BCCH + 1 CCCH

TS


Further TSs

8 SDCCH + 8 SACCH

Table 19: Expansion of signaling channels in order to ensure required signing capacity

Now SDCCH capacity is not the limiting factor anymore, but there is a reduction of the TCH capacity because of the reduction of TCH channels. Results for a cell with 4 TRXs: 3 TSs for signaling are also sufficient when SMS Cell Broadcast is enabled. It is still possible although the number of SDCCHs was decreased because the number of subscribers that can be served by means of 15 SDCCH sub-channels (i.e. 1843) exceeds subscriber capacity of TCHs (i.e. 841). Therefore the number of subscribers per cell is the same, regardless of whether SMS Cell Broadcast is enabled or not.

8.3

SDCCH in case of Dual Band Standard Cell

The example below shows the benefits of the Dual Band Standard Cell configuration in comparison to the Dual Band Cell (legacy approach). In case of a Dual Band Standard Cell only common BCCH is used whereas in case of Dual Band Cell there are two BCCHs (one per band). For description of Dual Band Standard Cell please refer to chapter 5.5. For better understanding of calculations described in this example please refer to chapter 7, where dimensioning rules were presented. Assumptions: 5 TRXs for 900 MHz frequency band, 5 TRXs for 1800 MHz frequency band, Traffic per subscriber on a TCH: loadsub, TCH = 25 mErl, Traffic per subscriber on a SDCCH: loadsub, SDCCH = 4 mErl, Blocking probability of TCH: BTCH = 2%, Blocking probability of SDCCH: BSDCCH = 0.5%, 100% Full Rate: FR% = 100%.


s

s Dual Band Cell

# TS = per band

Dual Band Standard Cell

TRX TS ⋅ = 5 ⋅ 8 = 40 band TRX

In order to fulfil restriction described in chapter 7 split of TS should be as follows: TSTCH: 37; TSsign: 3 These values can be found in tables 11 and 12 respectively (5 TRXs, 100% Full Rate).

Number of timeslots

# TS = number _ of _ bands ⋅

per cell

Total carried traffic on TCHs

Number of subscribers (TCH)

per band

TSTCH: 76; TSsign: 4 These values can be found in tables 11 and 12 respectively (10 TRXs (2 * 5 TRXs), 100% Full Rate). capTCH = 28.25 Erl (from Erlang table for 37 channels and 2% blocking probability) capTCH = 64.86 Erl

per cell per band

TRX TS ⋅ = 2 ⋅ 5 ⋅ 8 = 80 band TRX

(from Erlang table for 76 channels and 2% blocking) subTCH = 1130 (28.25 Erl / 25 mErl) subTCH = 2594

per cell

(64.86 Erl / 25 mErl) capSDCCH = 8.1 Erl

Total carried signaling load on SDCCHs

per band

(from Erlang table for 16 SDCCH sub-channels (2 TS) and 0.5% blocking probability) One of three signaling TSs is reserved for BCCH. capSDCCH = 14.2 Erl

per cell

(from Erlang table for 24 SDCCH sub-channels (3 TSs) and 0.5% blocking probability) One of four signaling TSs is reserved for BCCH. subSDCCH = 2025

per band Number of signaling subscribers

(8.1 Erl / 4 mErl) Signaling capacity sufficient (2025 > 1130) (9) subSDCCH = 3550

per cell

(14.2 Erl / 4 mErl) Signaling capacity sufficient (3550 > 2594)

9 Signaling capacity (number of users) should not be smaller than traffic capacity. For details regarding signaling capacity please refer to chapter 7. 60 Planning Guideline: SDCCH dimensioning

s

s Dual Band Cell Total number of served subscribers Total number of signaling timeslots Total number of SDCCH TSs

Dual Band Standard Cell

2260

2594

(1130 users per band) TSsign = 6 (3 per band; 1 BCCH per band)

TSsign =4

SDCCHTS = 4

SDCCHTS = 3

(2 SDCCH TSs per band)

(1 Common BCCH per cell)

Table 20: Calculation example of SDCCH in Dual Band Standard Cell

The total number of subscribers supported in a Dual Band Standard Cell is higher in terms of hard blocking (10). The number of required timeslots for SDCCH channels to support signaling is lower in the Dual Band Standard Cell (3 vs. 4) but this reduction is configuration dependent (because of the granularity during calculations) and it may happen that this comparison in case of other configurations will give the same result of required SDCCHs.

10 Hard blocking - The blocking due to no resources available. 61 Planning Guideline: SDCCH dimensioning

s

s 9

Appendix A: Siemens Traffic Model

Detailed values from the Siemens Traffic Model are included in table below.

Description

Dimension

Default values, to be adapted according to the customer's requirement

NMOC

( ) # Mobile Originating Call attempts per subscriber and BH 11

1/h

0.6

NMTC

( ) # Mobile Terminating Call attempts per subscriber and BH 12

1/h

0.4

NSMS

# SMS messages per subscriber and BH

1/h

0.2

NLR

# Location Requests per subscriber and BH

1/h

( ) 0 13

Parameter Subscriber related parameters

Mobility related parameters NLUP

# Location Updates per subscriber and BH (including IMSI Attach/Detach events)

1/h

2.0

NHO

#Intra-BSC HOs per subscriber and BH

1/h

0.5

IMSIAttach

# IMSI Attach per subscriber and BH

1/h

( ) 0 14

IMSIDetach

# IMSI Detach per subscriber and BH

1/h

( ) 0 15

Tmh

( ) Mean holding Time 16

Sec./CA

90

BTCH

Blocking probability for TCH channel

%

2

Link related parameters

Bsignaling

Blocking probability for signaling

%

0.5

loadsub, signaling

Signaling per subscriber

mErl

4

loadsub, TCH

Traffic per subscriber

mErl

25

Table 21: Siemens Trafic Model values

11 Including unsuccessful CAs. 12 Including unsuccessful CAs. 13 Typically a value of around N

LR

= 0.092 shall be taken into account.

14 Please refer to number of Location Updates (N

).

15 Please refer to number of Location Updates (N

).

LUP

LUP

16 The holding time of a CA (either successful or unsuccessful) is the time between the first and the last exchange of signaling information. 62 Planning Guideline: SDCCH dimensioning

s

s 10 Appendix B: Description of messages used in message flows This table contains short description of messages used in message flows presented in this document in chapter 3. For more detailed information about message flows please refer to [PMMF]. Message Acronym

Full Message Name

CHANNEL ACTIVATION ACKNOWLEDGE

CHNAK

Type

Interface

Abis RSL Message

CHNAV

Abis RSL (17) Message

CHANNEL REQUIRED

CHNRD

Abis RSL Message

CHANNEL REQUEST

CHNREQ

Um Message

CHANNEL ACTIVATION

ESTABLISH INDICATION

BTS

BSC

Notes BTS uses this message to acknowledge CHANNEL ACTIVATION message and activation of requested channel type. When BSC receives this message it does not necessarily mean that requested channel was activated without error.

BTS

This message reserves and activates channel on Um interface. This message contains information of required channel type (HR/FR), DTX (on/off), etc. BTS needs this information in order to activate transcoders (TRAU).

BTS

BSC

This message is sent by BTS as a response on CHANNEL REQUEST message received from MS.

MS

BTS

This message is used by MS in order to request channel when it is in idle state.

BSC

Message sent from BTS to BSC which indicates that the SET ASYNCHRONOUS BALANCED MODE frame (Um layer 2 connection setup message sent by MS) was received by the BTS for the activated channel (TCH or SDCCH).

BSC

ESTIN

Abis RSL Message

IMMEDIATE ASSIGNMENT COMMAND

IACMD

Abis RSL Message

BSC

BTS

Contains all information required for SDCCH channel assignment on Um interface. This message is used by BSC as a response on CHANNEL REQUIRED.

IMMEDIATE ASSIGNMENT

IMASS

DTAP (18) Message

BTS

MS

Message sent from BTS to MS as a response on receive IMMEDIATE ASSIGNMENT COMMAND from BSC.

IMMEDIATE

IMASSRJ

DTAP

BTS

MS

BSC may send IMMEDIATE

17 RSL – Radio Signaling Link (A

bis

BTS

protocol).

18 DTAP – Direct Transfer Application Part (Protocol (MS  Planning Guideline: SDCCH dimensioning

BSC, MS  63

MSC)).

s

s ASSIGNMENT REJECT

Message

ASSIGNMENT REJECT as an answer for CHANNEL REQUIRED if no SDCCHs are available.

PAGING REQUEST

PAGREQ

Um Message

BTS

MS

PAGING REQUEST is used to page the MS in case of MTC and SMS-MT while the MS is in 'idle' mode.

PAGING COMMAND

PGCMD

Abis RSL Message

BSC

BTS

Message sent from BSC as a response on paging message from the MSC.

SET ASYNCHRONOUS BALANCED MODE

SABM

Um layer2 Message

MS

BTS

MS sends this message after receive of IMMEDIATE ASSIGNMENT from BTS.

UNNUMBERED ACKNOWLEDGEMENT

UA

Um layer2 Message

BTS

MS

This frame is used to answer SET ASYNCHRONOUS BALANCED MODE frame. UNNUMBERED ACKNOWLEDGEMENT frame is used in order to acknowledge Layer2 connection (during establishing and terminating).

Table 22: Description of messages used in message flows


s

s 11 APPENDIX C: Use case: SDCCH creation for a cell For steps required for a creation of SDCCH channel for a cell please refer to [DB] where a detailed description of such a case can be found.


s

s 12 APPENDIX D: Parameters and settings Below a list of parameters relevant for this document was included. For a detailed description of presented parameters please refer to [DB].

12.1 Siemens BSS parameters relevant for SDCCH channel

Parameter meaning

Parameter

Description

Direct TCH assignment

DIRTCHASS

Direct TCH Assignment allows assignment of a TCH channel without previous assignment of an SDCCH.

Inter SDCCH handover

EISDCCHHO

This parameter determines whether Inter BSC SDCCH handover is enabled.

Forced handover

ENFORCHO

This parameter determines whether the BSC may send a FORCED HANDOVER REQUEST message for running SDCCH connections to the BTS.

UMTS SDCCH handover

EUSDCHO

This parameter determines whether intra-cell handover due to quality is enabled for SDCCH-SDCCH handovers.

Inter-cell handover for SDCCH

IERCHOSDCCH

This parameter determines whether Inter-cell SDCCH-SDCCH handover is enabled.

Intra-cell handover for SDCCH

IRACHOSDCCH

This parameter determines whether intra-cell handover due to quality is enabled for SDCCH-SDCCH handovers.

Maximum number of retransmissions

MAXRETR

This parameter defines the maximum number of retransmission attempts the MS can perform on the RACH if the previous attempts have been unsuccessful. The attempt procedure is presented on figure 3.

SDCCH Drop Rate

SDCCHDROR

This parameter indicates when its value is different from , that the KPI ‘SDCCH Drop Rate’ is observed for the feature ‘Quality of service alarms’.

SDCCH Loss Rate

SDCCHLOSR

This parameter indicates when its value is different from , that the KPI ‘SDCCH Loss Rate’ is observed for the feature ‘Quality of service alarms’.

Transparent messages

TRANSPM

This parameter is relevant for BR8.0 Performance Measurement Counter called ‘Mean number of busy SDCCHs per signaling procedure’ (MBUSYSSP; For more details about this measurement please refer to chapter 13.1 and [PMMF]). The purpose of this counter is to allow a more detailed observation of the SDCCH load with respect to the traffic type that was processed via the allocated SDCCH.

Table 23: Siemens BSS parameters relevant for SCCH channel


s

s 12.2 Parameters for Smooth Channel Modification Parameter meaning

Parameter

Description

Channel Pool Type

CHPOOLTYP

Channel Combination

CHTYPE

New tag has been inserted to identify the new TCHSD channel shared between TCH and SDCCH.

Sdcch Congestion Threshold

SDCCHCONGTH

Defines the SDCCH load threshold which causes the move of a TCHSD from the TCHSD_POOL to the SDCCH_BACKUP_POOL and vice versa.

Timer Guard Tchsd

TGUARDTCHSD

Interval of time after that the TCHSD can be released by the SDCCH_BACKUP_POOL to the TCHSD_POOL.

Identifies the pool type for TCHSD TSs.

Table 24: Parameters for SCM


s

s 13 Appendix E: Performance measurements and counters Below a list of counters relevant for this document was included. For a detailed description of presented counters please refer to [PMMF].

13.1 SDCCH related measurements Counter meaning

Counter

Counter Related to

Number of Defined SDCCHs

NDESDCCH

SDCCH Availability

Number of Available SDCCHs

NAVSDCCH

SDCCH Availability

Mean Number of Busy SDCCHs

MBUSYSDC

Busy SDCCHs

Maximum Number of Busy SDCCHs

MAXBUSDC

Busy SDCCHs

Number of Attempted SDCCH Seizures in a Period

NATTSDPE

SDCCH Seizure

Number of Successful SDCCH Seizures in a Period

NASUSDPE

SDCCH Seizure

Attempted SDCCH Seizures Meeting an SDCCH Blocked State

ATSDCMBS

SDCCH Seizure

Mean Number of Busy SDCCHs per Signaling Procedure

MBUSYSSP

SDCCH Seizure

Number of Successful Seizures for USSD Signaling

NSUSDSUS

SDCCH Seizure

All Available SDCCHs Allocated Time

ASDCALTI

SDCCH Blocking Time

Number of Invalid RACH Messages

NINVRACH

Invalid RACH (PRACH) Access

Table 25: SDCCH related measurements

13.2 TCH and SDCCH Assignment Related Measurements Counter meaning

Counter

Counter Related to

Attempted Immediate Assignment Procedure

ATIMASCA

Immediate Assignment Procedure

Successful Immediate Assignments of Signaling Channels

NSUCCHPC


Successful Immediate Assignment Procedure

SUIMASCA


Total Number of Assignment Attempts

TASSATT

Assignment Procedure

Total Number of Assignment Failures

TASSFAIL


Total Number of Successful Assignments

TASSSUCC


Table 26: TCH and SDCCH Assignment Related Measurements


s

s 13.3 Release and Loss of Dedicated Connections Related Measurements Counter meaning

Counter

Number of CLEAR COMMAND Messages

NRCLRCMD

Number of CLEAR REQUEST Messages

NRCLRREQ

Counter Related to Normal and Abnormal BSSMAP Release of Connected Resources Normal and Abnormal ( ) BSSMAP 19 Release of Connected Resources

Number of Lost Radio Links while using an SDCCH

NRFLSDCC

Normal and Abnormal BSSMAP Release of Connected Resources

Table 27: Release and Loss of Dedicated Connections Related Measurements

13.4 Handover Related Measurements Counter meaning

Counter

Counter Related to

Attempted Internal SDCCH Handovers Intercell

AISHINTE

Handover

Attempted Internal SDCCH Handovers Intracell

AISHINTR

Handover

Attempted MSC-Controlled SDCCH Handovers

AOINTESH

Handover

Successful Internal SDCCH Handovers Intercell

SISHINTE

Handover

Successful Internal SDCCH Handovers Intracell

SISHINTR

Handover

Successful MSC-Controlled SDCCH Handovers

SOINTESH

Handover

Unsuccessful Internal SDCCH Handovers Intracell with Loss of Connection

UISHIALC

Handover

Unsuccessful Internal SDCCH Handovers Intercell

UISHINTE

Handover

Unsuccessful Internal SDCCH Handovers Intracell

UISHINTR

Handover

Unsuccessful Internal SDCCH Handovers Intercell with Loss of Connection

UISHIRLC

Handover

Unsuccessful MSC-Controlled SDCCH Handovers with Loss of Connection

UMCSHLC

Handover

Unsuccessful MSC-Controlled SDCCH Handovers

UOINTESH

Handover

Table 28: Handover Related Measurements

19 BSSMAP - Base Station Subsystem Mobile Application Part. BSSMAP is used on the SCCP (Signaling Connection Control Part) protocol on SS7 (Signaling System number 7) on the A interface. BSSMAP is taking care of messages which have to be processed by the BSC. In general this applies to all messages to and from MSC. 69 Planning Guideline: SDCCH dimensioning

s

s 13.5 Miscellaneous Measurements Counter meaning

Counter

Number of Channel Allocation Requests Not Served in the Highest Layer or at all

CHALNHLY

Counter Related to Service Dependent Channel Allocation

Table 29: Miscellaneous Measurements

13.6 SCM Related Measurements Counter meaning

Counter

Counter Related to

Mean Duration a TCHSD with TCHSD_POOL can be Used as SDCCH

MDURTCSD

Number of Available TCHSD

NAVTCHSD

TCHSD Availability

Number of Defined TCHSD

NDFTCHSD

TCHSD Availability

Number of TCH-SDCCH Channel Modifications

NTCHSDCM

TCHSD SCM

TCHSD SCM

Table 30: SCM Related Measurements


s

SDCCH_Dimensioning

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