01 Mn1889eu11mn 0001 Introduction

Introduction

Siemens

Introduction

Contents 1 1.1 1.2 2 2.1 2.2 2.3 3 3.1 3.2 4 4.1 4.2 4.3 5 5.1 5.2 5.3 5.4 5.5 6 6.1 7 8

GPRS network Architecture of a GPRS network Interfaces Protocols used in GSM-PLMN and in GPRS/E-GPRS-PLMN Overview: protocols used in GSM-PLMN Overview: protocols used in GPRS/E-GPRS PLMN (user data transmission) Overview: protocols used in GPRS/E-GPRS PLMN (signaling) Characterization of a packet data transmission PDP context Quality of service (QoS) State values Mobility management states Packet data protocol states Mobile classes and radio resource states Air interface transmission GPRS coding schemes E-GPRS channel coding E-GPRS link quality control Packet data channels Multiframe structure in GPRS/E-GPRS Hardware impacts of GPRS/E-GPRS on SBS Affected modules in the BTSE and BSC Exercise Solution

MN1889EU11MN_0001 © 2005 Siemens AG

3 4 6 9 10 12 18 21 22 24 27 28 30 32 35 36 42 48 50 54 57 58 63 67

1

Siemens

2

Introduction


Introduction

1

Siemens

GPRS network


3

Introduction

Siemens

1.1

Architecture of a GPRS network

For introducing GPRS, the logical GSM architecture is extended by two functional units: The Serving GPRS Support Node SGSN is on the same hierarchic level as MSC and has functions comparable to those of a Visited MSC (VMSC). The Gateway GPRS Support Node GGSN has functions comparable with those of a Gateway MSC (GMSC) and offers interworking functions for establishing contact between the GSM/GPRS-PLMN and external packet data networks PDN. In addition to GSN, extensions of functions in other GSM functional units are necessary: In the BSS a Packet Control Unit PCU ensures the reception/adaptation of packet data from SGSN into BSS and vice versa. The Channel Codec Unit CCU supports the new coding schemes used by GPRS and the modulation and coding schemes used by EGPRS. GPRS subscriber data are added to the HLR. On the following pages of this script this extension will be termed GPRS Register GR.

4


Introduction

Siemens

GPRS - Architecture Channel Codec Unit CCU in BTS for channel coding

GPRS subscription data (GPRS Register GR)

HLR

BSS

Mobile DTE

PCU

Packet Control Unit PCU for protocol conversion & radio resource management SGSN Serving GPRS Support Node SLR SGSN Location Register GGSN Gateway GPRS Support Node

VMSC / VLR

GMSC

PSTN ISDN

SGSN / SLR

GGSN

Internet Intranet X.25

New network entities: • SGSN (access to BSS) • GGSN (access to PDN)

Fig. 1 GPRS architecture


5

Introduction

Siemens

1.2

Interfaces

Beside the interfaces in the “classical” GSM PLMN, a number of new interfaces are defined for the implementation of GPRS services based on the introduction of the new network elements SGSN and GGSN. The interfaces Gi (external PDN-GGSN), Gn (GSN-GSN), Gb (SGSN-BSS) and Gd (SGSN-SMS/IWMSC) serve for the transport of both signaling data and of user data. Interfaces Gp (GSN-GSN in external PLMNs), Gf (SGSN-EIR), Gc (GGSN-HLR), Gs (SGSN-MSC/VLR) and Gr (SGSN-HLR) serve exclusively for the transfer of signaling data.

6


Introduction

Siemens

Signalling & user data Signalling

SMS-GMSC SMS-IWMSC

E

C Gd

D

MSC/VLR

Gb

Um MS

BSS Gn

SGSN

HLR/(GR)

Gr

Gs

A

SMS-SC

Gc Gi

Gn

SGSN Gp

GGSN

PDN

TE

Gf EIR

GGSN other PLMNs

Fig. 2 GPRS and EGPRS interfaces


7

Siemens

8

Introduction


Introduction

2

Siemens

Protocols used in GSM-PLMN and in GPRS/E-GPRS-PLMN


9

Introduction

Siemens

2.1

Overview: protocols used in GSM-PLMN

In GSM-PLMN phase 1/2 the Signaling System No. 7 (SS7) is used for the transmission of signaling information between the components of the network switching sub-system NSS (interfaces B-G), as well as between MSC and BSC (Ainterface) and in direction of the external ISDN networks. SS7 comprises 4 levels, of which the lowest 3 levels are combined to form the Message Transfer Part (MTP) whereas level 4 contains different user parts depending on the tasks to be performed. Level 1 serves for the physical transmission (physical layer) of data and for the provision of the requested equipment. (e.g. cable connection, radio relay links, ...). In the GSM-PLMN, PCM30 or PCM24 (E1/T1) are used for the realization of level 1 functions. Level 2 serves for the safe transmission of signaling information (link layer). Its functions include fault location and clearance across a sub-part of the transport. Level 3 determines the entire transport link (network layer) including the transport of information in the event of faults in individual signaling points (e.g. overload). The Mobile Application Part (MAP) is the most important User Part UP (level 4). It regulates the mobility aspects in the GSM-PLMN between the MSCs as well as between MSCs and registers. Its functions include amongst others: Updating and clearance of location information in the VLR, storing of routing information in the HLR, updating and supplementing of user profiles in the HLR&VLR, Inter-MSC handover, ... The ISDN User Part (ISUP) handles the connection-oriented signaling between MSCs and external networks. GSM-specific signaling between MSC and BSC is defined in the Base Station System Application Part (BSSAP). The BSSAP is subdivided into the Direct Transfer Application Part (DTAP) used for the BSC-transparent transport of signaling (call control CC and mobility management MM) between MS and MSC, and the BSS Management Application Part (BSSMAP). The Signaling Connection Control Part (SCCP) and Transaction Capabilities Application Part (TCAP) are user-neutral user parts which serve for the support of complex MAP applications. SCCP can be used also for the support of ISUP and BSSAP. Layer1 and layer 2 tasks (Link Access Protocol for D-channel) on the Asub and Abis interfaces have been slightly modified as compared to SS7. The radio interface Um in the GSM-PLMN is set up of three layers. Layer 1 serves for the physical transmission and includes aspects as e.g. logical channels, FDMA, TDMA, multiframes, channel coding, etc.) Layer 2 functions on Um are performed by a modified LAPD protocol (LAPDm).

10


Introduction

Siemens

Layer 3 on the Um radio interface is subdivided into three sublayers: radio resource management RR (channel administration, power control and handover), mobility management MM and connection management CM (set-up, operation and cleardown of services). The connection management consists of: call control CC, supplementary services support SS and short message services SMS support.

CM CC

SS

HLR

SMS

AC

VLR

EIR

MM RR

MAP

LAPDm L1

TCAP SCCP L3 L2 L1

RSL/O&M/L2ML

x

LAPD L1

BTS MS

BSC

MTP

MSC

BSSAP

ISUP SCCP

BSSMAP DTAP

OMC-B

SCCP

MTP

ISDN

OMC-B

MTP

Fig. 3 Protocols used in the GSM-PLMN


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Introduction

Siemens

2.2

Overview: protocols used in GPRS/E-GPRS PLMN (user data transmission)

The transmission plane has a layered protocol structure for the transfer of user information. It includes the control procedures associated with the information transfer, e.g. flow control, fault detection and fault clearance. If the application is internet access for example the GPRS/E-GPRS MS (WWW client) and the PDN (WWW server) will exchange IP packets. This is the IP protocol below the application in the stack of the MS and the IP on top of the stack of the GGSN. The recommendations have defined that X.25 protocol is possible too. In case of IP the MS has to be part of the IP world and needs to be identified by an IP address which can be either temporary or static. This IP address has to remain the same as long as the PDP which is related to this application is active. This is necessary because the PDN is not able to handle the mobility of the subscriber. If the GPRS/E-GPRS MS is moving to a cell in the service area of another SGSN the GPRS/E-GPRS network has to solve the problem by the IP layer on the Gn interface above the L2 layers. In consequence the fact that the GPRS/E-GPRS user is a mobile user is not to be seen by the PDN, the user data is tunneled transparently. The air interface makes it necessary to introduce protocols which adopt the size of the packets. They perform segmentation/re-assembly depending on the direction of the packets to be able to send IP packets via an air interface which consists of bursts with a fixed bit structure. One of the main advantages of GPRS/E-GPRS compared to HSCSD is that it is packet switched. This can only be done by introducing new network elements using new hardware/protocols and by changes in the protocol structure on Um to enable packet switching. The latter is done by the MAC procedure. The purpose of the different layers is described below: GTP (GPRS Tunneling Protocol) The GTP task is to tunnel user data and user signaling between the GPRS support nodes GSN of the GPRS backbone network. The data packets (protocol data units PDUs) supplied by different packet data protocols PDPs, e.g. X.25 or IP, have to be encapsulated / de-capsulated by the GTP prior to tunneling. GTP is specified in Rec.09.60.

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Introduction

Siemens

GPRS/E-GPRS transmission plane Application IP / X.25

IP / X.25 Relay SNDCP GTP

SNDCP LLC

LLC

RLC

RLC

MAC

UDP / TCP

UDP / TCP

IP

IP

L2

L2

L1

L1

BSSGP

NS

NS

FR/IP

FR/IP

L1

L1

MAC

GSM RF

MS

Relay BSSGP

GSM RF

Um

SNDCP: SubNetwork Dependent Convergence Protocol LLC: Logical Link Control RLC: Radio Link Control MAC: Medium Access Control

BSS

Gb BSSGP: BSS GPRS Protocol NS: Network Service FR: Frame Relay

GTP

SGSN

Gn

GGSN

Gi

GTP: GPRS Tunnelling Protocol UDP: User Datagram Protocol TCP: Transmission Control Protocol IP: Internet Protocol

Fig. 4 Protocols used in the GPRS/E-GPRS transmission plane


13

Siemens

Introduction

UDP / TCP (User Datagram Protocol / Transmission Control Protocol) UDP and TCP respectively are used for the transfer of data packets encapsulated by the GTP across the GPRS backbone network. The protocol needed for this is called UDP. It has to be supported by all GSNs as minimum solution since it transports data packets (GTP PDUs) of protocols which require a safe data connection (e.g. IP). UDP also protects transmission against data corruption/mutilation. TCPs have to be supported in the GSNs whenever data packets of protocols have to be transported, requiring safe data connections (e.g. X.25). TCP ensures the flow control and provides protection against loss of data and data corruption.

IP (Internet Protocol) IP is used in the GPRS backbone network for the routing of user data and network information. At the beginning, the GPRS backbone network can be based on the IP version 4. However, the objective envisaged is IP version 6.

SNDCP (SubNetwork Dependent Convergence Protocol): The SNDCP supports the following functions: compression/segmentation and joining, multiplexing and de-multiplexing of data packets onto one or several LLC SAPs (service access points). The compression function is applied to the user data of the data packet and (if applicable) to the packet header. Segmentation is required to limit the size of the data packets which is transferred by the LLC as one single unit via the radio interface. The SNDCP is specified in the GSM Rec. 04.65.

LLC (Logical Link Control): The LLC layer realizes a highly reliable ciphered logical connection and thus provides the basis for maintaining communication between the SGSN and the MS. From the point of view of the LLC layer, there is a complete connection between SGSN and MS, even if the RLC/MAC do not support a physical connection, i.e. even if no data packets are transferred at that point in time. A physical connection is set-up by the RLC/MAC layer only if the LLC layer supplies the data required for transmission. LLC layer has several access points to be able to transport various types of data; also, it distinguishes between several “quality of service QoS” classes. The LLC layer is also responsible for carrying out the ciphering function in the GPRS network. LLC is specified in GSM Rec. 04.64.

BSSGP (BSS GPRS Protocol): The BSSGP transports the LLC frames as well as routing and QoS-related information between the BSS (PCU) and the SGSN. The BSSGP does not carry out fault correction. It is specified in GSM Rec. 08.18.

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Introduction

Siemens



SNDCP LLC

LLC

RLC

RLC

MAC

UDP / TCP

UDP / TCP

IP

IP

L2

L2

L1

L1

BSSGP

NS

NS

FR/IP

FR/IP

L1

L1

MAC

GSM RF

MS

Relay BSSGP

GSM RF

Um


BSS


GTP

SGSN

Gn

GGSN

Gi




15

Siemens

Introduction

NS (Network Service), FR (Frame Relay)/IP: The Network Service (NS) layer transports the BSSGP data packets. NS is based on frame relay or on IP, which thus represents the link layer protocol for the connection between SGSN and PCU (Gb interface). NS is specified in GSM Rec. 08.16.

RLC (Radio Link Control) / MAC (Medium Access Control): RLC and MAC are the layers used for the implementation of a reliable physical connection via the radio interface on which data packets are transported. RLC and MAC are closely associated with each other and are defined in GSM Rec. 04.60. RLC (Radio Link Control): The RLC function supplies a reliable connection (provides BEC) via the radio interface. RLC segments LLC frames and re-assembles them respectively. In addition, the RLC carries out sub-multiplexing in order to place more than one MS on a physical channel and to bundle up to 8 physical channels for one MS. MAC (Medium Access Control): The MAC function controls the signaling procedures via Um which are required to obtain network access (access signaling procedures), e.g. request and grant of radio resources (packet data channel PDCH). Furthermore, the MAC function controls the mapping of LLC frames to the physical channels of the radio interface. The identifiers (TFI "Temporary Flow Identifier, USF "Uplink State Flag") which are used by the MAC protocol enable the sharing of physical channels by several MSs. Different mechanisms of allocation of radio resources may be used, dynamic or fixed allocation.

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Introduction

Siemens



SNDCP LLC

LLC

RLC

RLC

MAC

MAC

GSM RF

MS

Relay BSSGP

GSM RF

Um


BSS

UDP / TCP

UDP / TCP

IP

IP

L2

L2

L1

L1

BSSGP

NS

NS

FR/IP

FR/IP

L1

L1


GTP

SGSN

Gn

GGSN

Gi




17

Introduction

Siemens

2.3

Overview: protocols used in GPRS/E-GPRS PLMN (signaling)

The signaling plane consists of protocols for the control and support of transmission plane functions:

• Control of GPRS/E-GPRS network access, e.g. „attaching“ and „detaching“ • Control of the data elements (attributes) of an established network connection and activation of the packet data protocol PDP (e.g. X.25 / IP) addresses.

• Control of the routing path of an established connection in terms of subscriber mobility support.

• Support of the network resource allocation to account for various user requests. • Supplementary services implementation Signaling Plane MS-SGSN: In addition to the protocols of the transmission plane a further plane, based on the functions GSM RF, RLC/MAC and LLC, is required: GMM/SM (GPRS Mobility Management and Session Management) The GMM/SM protocol supports mobility management functions such as GPRS attach, GPRS detach, safeguarding functions, routing area & location update), and session management functions as PDP context activation & deactivation & modification.

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Introduction

Siemens

GPRS/E-GPRS signaling plane

MS-SGSN GMM/SM

GMM/SM

GPRS Mobility Management & Session Management

GPRS Mobility Management & Session Management

LLC

LLC Relay

RLC

RLC

MAC

MAC

GSM RF

GSM RF

MS

Um

BSS

BSSGP

BSSGP

NS

NS

FR/IP

FR/IP

L1

L1

Gb

SGSN

Fig. 7 Protocols used in the GPRS/E-GPRS signaling plane


19

Siemens

20

Introduction


Introduction

3

Siemens

Characterization of a packet data transmission


21

Introduction

Siemens

3.1

PDP context

The PDP context is the description of the services a subscriber is allowed to use. A subscriber may also use different packet data protocols (PDPs). The following parameters are available for each PDP: The packet network address is necessary to identify the subscriber in the public data net. Either dynamically assigned (temporary) addresses or (in the future) static addresses are used in case of IP. The problem of the dynamic addresses will be overcome with the change from Ipv4 to IPv6. In GPRS two layer 2 protocols are allowed, X.25 or IP. The Quality of Service QoS: QoS describes various parameters. The subscriber profile defines the highest values of the QoS parameters that can be used by the subscriber. The screening profile: This profile depends on the PDP used and on the capacity of the GPRS nodes. It serves to restrict acceptance during transmission/reception of packet data. For example, a subscriber can be restricted with respect to his possible location, or with respect to certain specific applications. The GGSN address: The GGSN address indicates which GGSN is used by the subscriber. In this way the point of access to external packet data networks PDN is defined. The internal routing of the data is done by IP protocol, the GSNs will have IP addresses. A DNS function is needed to find the destination of the data packets (address translating: e.g. www.gsn-xxx.com = 129.64.39.123)

22


Introduction

Siemens

GPRS Subscriber Profile Subscription profile used Packet Data Protocols PDP possible: 1 Subscriber - different PDPs / 1 PDP with different addresses

QoS Quality of Service

Packet network address

highest QoSparameter values in Subscriber Profile

static/dynamic IP address

PDP Parameter

GGSN address Access to external PDN

Screening Profile limits receiving / emission of data packets

Fig. 8 PDP parameters


23

Introduction

Siemens

3.2

Quality of service (QoS)

The different applications that will make use of packet-oriented data transmission via GPRS require different qualities of transmission. The quality of service profile (Rec. 02.60, 03.60) permits selection of the following attributes: Precedence Class Three different classes have been defined to allow assessment of the importance of the data packets, in case of limited resources or overload: Delay Class GSM Rec.02.60 defines 4 delay classes (1 to 4). However, a PLMN only needs to realize part of these. The minimum requirement is the support of the so-called „best effort delay class“ (Class 4). Delay requirements (maximum delay) concern the delay of transported data through the entire GPRS network.ified unspecified Reliability Class Transmission reliability is defined with respect to the probability of data loss, data delivery beyond/outside the sequence, twofold data delivery, and data falsification (probabilities 10-2 to 10-9). 5 reliability classes (1 to 5) have been defined, 1 guaranteeing the highest and 5 the lowest degree of reliability. Highest reliability (Class 1) is required for error-sensitive, non-real-time applications which have no possibility of compensating for data loss; lowest reliability (Class 5) is needed for real-time applications which can get over data loss. Peak Throughput Class The peak throughput class defines the maximum data rate to be expected (in bytes/s). However, there is no guarantee that this data rate/throughput can be achieved over a certain period of time. This depends on the capability of the MS and the availability of radio resources. 9 throughput classes have been defined, ranging from Class 1 with 1000 bytes/s (8 kbit/s) to 256,000 bytes (2048 kbit/s). The maximum data rate doubles from one class to the next. Mean Throughput Class The mean throughput class represents the mean data rate/throughput to be expected for data transport via the GPRS network during an activated link. A total of 19 classes have been defined. Class 1 is „best effort“ and means that the data rate for the MS is made available on the basis of demand and availability of resources. Class 2 stands for 100 bytes/h (0.22 bit/s), class 3 for 200 bytes/h, class 4 for 500 bytes/h and class 5 for 1000 bytes/h, etc. till Class 19 which stands for 50000000 bytes/h (111 kbit/s).

24


Introduction

Siemens

Quality of Service QoS - Profile Precedence Class 1: high priority 2: normal priority 3: low priority

Delay Class Delay Class

mean transfer delay (sec) < 0,5 <5 < 50 unspecified

1 2 3 4 (Best Effort) minimum requirements

95% delay (sec) < 1,5 < 25 < 250 unspecified

mean transfer delay (sec) <2 < 15 < 75 unspecified

SDU size: 128 Byte

95% delay (sec) <7 < 75 < 375 unspecified

1024 Byte

Reliability Class 1 - 5 (lowest): • data loss probability • out of sequence probability • duplicate probability • corrupt data probability probabilities 10-9 - 10-2

peak throughput Class 1 - 9: > 8 kbit/s - >2048 kbit/s maximum data rate no guarantee for this data rates over a longer period of time

mean throughput Class medium, guaranteed data rate; Class 1 - 19: 1: best effort 100 Byte/h (0,22 bit/s) / 200 / 500 / 1000 / ... / 50 Mio. Byte/h (111 kbit/s)

Fig. 9 Quality of Service parameters

Since release'99 these QoS attributes are mapped to the four different UMTS traffic classes: Traffic class

Conversation al

Streaming

Interactive

Background

Fundamental characteristics

• - preserve

- preserve time relation

- preserve payload content

- preserve payload content

- request response pattern

- not time critical

web browsing

email downloading

time relation

• - low delay

Example


voice

streaming audio/video

25

Siemens

26

Introduction


Introduction

4

Siemens

State values


27

Introduction

Siemens

4.1

Mobility management states

"Idle" state A mobile station MS in the idle state is detached from the GPRS. Only GPRS subscription data is available in the HLR. No further information exists in other network units such as SGSN and GGSN. It is not possible to activate a packet data protocol PDP or to maintain a PDP in its active state. The GPRS MS must monitor the BCCH to determine the availability of cells which support GPRS services. Accordingly, the GPRS MS can carry out PLMN and cell selection procedures. To exit idle state, the MS must execute the “attach” procedure. Upon successful completion of this procedure, the MS changes to ready state. "Standby" state In the standby state the GPRS MS is attached to the GPRS network. The GPRS and the SGSN have a mobility management context comparable to the circuit switched connections. The MS monitors the broadcast channel to determine the availability of cells offering GPRS services and also the paging channel PCH, to be informed about paging requests. The SGSN recognizes/stores the routing area RA of the GPRS-MS. The routing area is a sub-unit of the location area LA, in other words a more detailed determination of the GPRS-MS location. The GPRS-MS informs the SGSN about changes of the routing area and answers paging requests.

"Ready" state In the ready state, the SGSN detects the current cell of the GPRS-MS beyond the routing area RA of the GPRS-MS. If the GPRS-MS changes cells, it in-forms the SGSN. Paging is thus superfluous in the ready state. The DL packet data transfer can be performed any time. Ready state does not mean that a physical connection is established between SGSN and MS. Only in the ready state, SGSN and MS can transfer data packets. MS and SGSN exit ready state upon expiry of a ready timer or in case of a faulty packet data transmission and change to standby state. Upon logoff, i.e. execution of a detach procedure, MS and SGSN exit ready state and change to idle state.

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Introduction

Siemens

MM States • SGSN & GGSN without MS information • only HLR contains subscription data • no PDP context can be activated

IDLE state

• MS observes BCCH • PLMN- & Cell Selection

GPRS attach

READY

• SGSN knows Routing Area & cell !! • UL & DL packet transmission possible

expiry of mobile reachable timer

state

SGSN: Paging / MS: initiates Transfer

• SGSN ↔ MS: MM-Context • SGSN knows Routing Area

STANDBY state

GPRS detach

• MS initiates Cell Update

expiry of READY timer / transmission errors • MS observes BCCH, PBCCH, PCH • initiates RA-Update • reacts to Paging Request

Fig. 10 Mobility Management states


29

Introduction

Siemens

4.2

Packet data protocol states

There are separate state circles for every authorized PDP of a GPRS-MS

"Inactive" State The inactive state of a PDP means that this PDP is not operating at that moment. There is no routing context in the MS, SGSN and GGSN. A transition in the active state is only possible if there is a mobility management connection and if MS and SGSN are in the standby or ready state. No data transfer is possible in the inactive state. Data packets which reach the GPRS network are either rejected or ignored.

"Active" State In the active state the MS, GGSN and SGSN are in a routing context. Data can be transmitted or received by the MS. The active state is ended explicitly if the MS deactivates a certain PDP. With GPRS detach and expiry of the standby timer, all the activated PDP are deactivated, too.

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Introduction

Siemens

PDP States

• PDP not activated • no Routing-context for MS, SGSN & GGSN

INACTIVE state

• no data transmission possible !

Transition to „Active“ State only if MM-context exists ( MS & SGSN: STANDBY / READY)

De-activation PDP context / GPRS detach expire STANDBY timer

• Routing context for MS, SGSN & GGSN

Activation PDP context

ACTIVE state

• Data transmission possible !

Fig. 11 Packet Data Protocol states


31

Introduction

Siemens

4.3

Mobile classes and radio resource states

A GPRS MS can work in three different operational modes. The operational mode depends on the service an MS is attached to (GPRS or GPRS and other GSM services) and on the mobile station’s capacity of simultaneously handling GPRS and other GSM services:

• Class A operational mode: The MS is attached to GPRS and other GSM services

and the MS supports the simultaneous handling of GPRS and other GSM services.

• Class B operational mode: The MS is attached to GPRS and other GSM services, but the MS cannot handle them simultaneously.

• Class C operational mode: The MS is attached exclusively to GPRS services. Depending on the different mode of operation a mobile can be in one of the following RR states:

• (packet) idle mode • packet transfer mode (acknowledged or unacknowledged transmission) • dedicated mode • dual transfer mode (DTM, for class A MS)

32


Introduction

Siemens

RR States

Dual Transfer mode ps & cs connection

Dedicated mode

Packet Transfer mode

cs connection

ps connection

(Packet) Idle mode no connection

Fig. 12 Radio Resource states


33

Siemens

34

Introduction


Introduction

5

Siemens

Air interface transmission


35

Introduction

Siemens

5.1

GPRS coding schemes

Channel coding starts with the division of digital information into transferable blocks. These radio blocks, i.e. the data to be transferred (prior to encoding) comprise:

• a header for the Medium Access Control MAC (MAC Header) • signaling information (RLC/MAC Signaling Block) or user information (RLC Data Block) and

• a Block Check Sequence BCS. The functional blocks (radio blocks) are protected by convolutional coding against loss of data. Furthermore, channel coding includes a process of interleaving, i.e. different arrangement in time. In the case of GPRS, interleaving is carried out across four consecutive TDMA frames i.e. to 8 blocks with 57 bits each. Four coding schemes are defined for GPRS (Rec. 03.64): CS-1 to CS-4. These can be used alternatively depending on the information to be transferred and on the radio interface’s quality.

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Introduction

Siemens

Channel Coding

4 GPRS Coding Schemes :

CS-1, -2, -3, -4 Radio Block RLC Data Block

user data

MAC Header

signaling

MAC Header RLC/MAC Control Block

Convolutional coding (not CS-4)

BCS

Radio Block

rate 1/2 convolutional coding Coded Radio Block

Puncturing (only CS-2, CS-3)

Interleaving

BCS

puncturing Radio Block (456 Bits)

57 Bit

57 Bit

57 Bit

•••

57 Bit

57 Bit

8 blocks on 4 bursts

Allocation of PDCH for transmission of 1 or 4 Radio Blocks (4 or 16 TDMA frames)

Fig. 13 Channel Coding, RLC/MAC blocks, redundancy


37

Siemens

Introduction

Coding Schemes: CS-1: CS-1 uses the same coding scheme as specified by Rec. 05.03 for the SDCCH. It comprises a half rate convolutional code for FEC forward error correction. CS-1 corresponds to a data rate of 9.05 kbit/s. CS-2 and CS-3 are punctured version of the same half rate convolutional code as CS-1. The coded bits are numbered starting from 0 and certain punctured bits are removed. CS-2: With CS-2 the punctured bits have numbers 4 ∗ i + 3 with i = 3,...,146 (exception: i = 9, 21, 33, 45, 57, 69, 81, 93, 105, 117, 129, 141). This means that none of the first 12 bits is punctured. CS-2 corresponds to a data rate of 13.4 kbit/s. Remark: For CS-2 the puncturing pattern must be adapted to the future new TRAU frame format in order to be used via the Abis interface (e.g. more bits must be punctured to make space for RLC signaling). CS-3: With CS-3 the punctured bits have numbers 6 ∗ i + 3 and 6 ∗ i + 5 with i = 2,...,111. CS-3 correspond to a data rate of 15.6 kbit/s. CS-4: CS-4 has no redundancy (no FEC) and corresponds to a data rate of 21.4 kbit/s. By bundling up to 8 packet data channels of one carrier into one MS, transmission rates up to 171.2 kbit/s are possible.

38


Introduction

Siemens

Channel Coding: Coding Schemes CS-1 9.05 kbit/s

CS-2

CS-3

13.4 kbit/s

15.6 kbit/s

CS-4

different redundancy (FEC) → Quality Um

21.4 kbit/s

Coding Scheme

Code Rate

Radio Block*

CS-1

1/2

181

456

0

CS-2

≈2/3

268

588

132

13.4

CS-3

≈3/4

312

676

220

15.6

CS-4

1

428

456

0

21.4

* Radio Block without Uplink State Flag USF & Block Check Sequence BCS

common coding & interleaving for 4 Normal Bursts: 456 Bit coded user data

Coded Punctured Data Rate Bits Bits kbit/s 9.05

bundling 1..8 TS

max. 171,2 kbit/s

Fig. 14 Coding schemes of GPRS, CS1 with high redundancy, CS4 no redundancy, radio blocks


39

Siemens

Introduction

In the beginning of GPRS, on the Abis interface transport capacity was restricted to 16 kbit/s owing to the fact that existing TRAU frames were used. For this reason, only coding schemes CS-1 and CS-2 were supported up to GR2.0/BR6.0. The transmission of data for CS-3 and CS-4 requires larger transport capacities on Abis, which are realized as 'Flexible Abis Allocation Strategy (FAAS)'. Out of the different coding schemes, CS-1 is particularly important. Due to the high redundancy of CS-1 this is well suited to serve as a safe basic coding for RLC/MAC control blocks. Under favorable radio transmission conditions, CS-2 achieves higher transmission rates, with a maximum at 12 kbit/s. However, the rate of transmission depends more strongly on the C/I ratio than with CS-1. This is even more true of coding schemes CS-3 and CS-4, respectively, whose transmission rates are considerably higher than those of CS-1 and CS-2 under good radio transmission conditions; but they rapidly decrease if the quality of the radio transmission interface gets worse.

40


Introduction

Siemens

• Introduction: CS-1 (9.05 kbit/s & CS-2 (13.4 kbit/s) • CS-1: basic coding for RLC/MAC data & control blocks • no CS-3 (15.6 kbit/s), CS-4 (21.4 kbit/s) → Abis limitation (current TRAU frames: 16 kbit/s)

Channel Coding

CS 1 - 4: Bit Rate Comparison 20 18

CS1 CS2 CS3 CS4

Net Throughput (kbit/s)

16 14 12 10 8 6 4 2 0 18

17

16

15

14

13

12

11

10

9

8

7

6

Carrier / Interference C/I (dB)

5

Fig. 15 The throughput of the 4 different GPRS coding schemes as function of C/I


41

Introduction

Siemens

5.2

E-GPRS channel coding

9 coding schemes have been developed for EGPRS. The following table shows the important properties of the coding schemes for EGPRS: Coding Scheme

Modulation

User data rate (kbit/s)

Code rate

Puncturing schemes

Useful bits

Family

MCS-1

GMSK

8.8

0.53

2

176

C

MCS-2

GMSK

11.2

0.66

2

224

B

MCS-3

GMSK

13.6

0.80

3

296

A (padding)

14.8

272+24

MCS-4

GMSK

17.6

1.00

3

352

C

MCS-5

8PSK

22.4

0.37

2

448

B

MCS-6

8PSK

27.2

0.49

2

592

A (padding)

29.6

544+48

MCS-7

8PSK

44.8

0.76

3

2*448

B

MCS-8

8PSK

54.4

0.92

3

2*544

A

MCS-9

8PSK

59.2

1.00

3

2*592

A

The timeframe in which the bits are delivered is always 20 ms. For MCS1-6 always one RLC block is delivered in this time, in MCS7-9 two RLC blocks are delivered to the coding unit and handled separately.

42


Introduction

Siemens

interface 0 PTDCH(n=5-8)

PTDCH(n=5-8)

downlink

uplink

RLC block 31+Q0 bits 5.1.n.2.1

RLC block 31+Q0 bits 5.1.n.1.1 interface 1

block code in: 3 bits out: 12 bits 5.1.5.1.2

cyclic code (no tail) in: 28 bits out: 36 bits 5.1.5.1.3

cyclic code + tail in: Q0 bits out: Q1 bits 5.1.n.1.4

convolutional code k=7, rate 9/17 in: 36 bits out: 68 bits 5.1.5.1.3

convolutional code k=7, rate r in: Q1 bits out: 372 bits 5.1.n.1.4


PTDCH(n=9,10)

PTDCH(n=9,10)

PTDCH(n=11-13)

uplink

downlink






PTDCH(n=11-13) uplink

downlink


RLC block 40+Q0 bits 5.1.n.1.1 block code in: 3 bits out: 36 bits 5.1.9.1.2




interface 2


convolutional code k=7, rate r in: Q1 bits out: 372 bits 5.1.n.1.4

convolutional code k=7, rate 0.33 in: 33 bits out: 100 bits 5.1.9.1.3


convolutional convolutional code code k=7, rate 45/124 k=7, rate r in: 45 bits in: Q1 bits out: 124 bits out: 1224 bits 5.1.11.1.3 5.1.n.1.4


interface 3

downlink reordering and partitioning +code identifier in: 456 bits out: 8 blocks 5.1.5.1.5

block rectangular interleaving in: 8 blocks out: pairs of blocks 4.1.4 interface 4

uplink

reordering and partitioning +code identifier in: 456 bits out: 8 blocks 5.1.5.2.4

block rectangular interleaving in: 100 bits out: 100 bits






5.1.9.1.5

5.1.9.1.5

5.1.9.2.4

5.1.11.1.5

5.1.11.1.5

5.1.11.2.4

downlink partitioning +code identifier in: 1392 bits out: pair of blocks 5.1.9.1.6

uplink partitioning +code identifier in: 1392 bits out: pair of blocks 5.1.9.2.5

downlink partitioning +code identifier in: 1392 bits out: pair of blocks 5.1.11.1.6

uplink partitioning +code identifier in: 1392 bits out: pair of blocks 5.1.11.2.5

encryption unit

Fig. 16 Coding and interleaving principles for different MCS, as defined in GSM 05.03


43

Introduction

Siemens

EGPRS Coding scheme families The different coding schemes can be classified into families as defined in the table above. These families make use of similar principles in the coding, i.e. the number of useful bits in one coding scheme with a high data transmission rate is multiples of the number of useful bits of slower coding schemes. Note that within one family different modulation techniques can be used.

44


Introduction

Siemens

MCS-3 Family A

37 octets

37 octets

37 octets

37 octets

MCS-6 MCS-9 MCS-3 34+3 octets 34+3 octets Family A padding

MCS-6 34 octets

34 octets

34 octets

34 octets

MCS-8 MCS-2 Family B

28 octets

28 octets

28 octets

28 octets

MCS-5 MCS-7 MCS-1 Family C

22 octets

22 octets

MCS-4

Fig. 17 Coding scheme families for EGPRS


45

Introduction

Siemens

Every data packet consists of headers and the payload. Further information bits are needed for the control of the data transmission. As an example, the handling of MCS9 data blocks is shown in the figure below. Note that three essential parts of the coding can be distinguished:

• the Uplink State Flag (USF), • the Radio Link Control and Medium Access Control headers (RLC/MAC) along with the header check sequence (HCS), and

• the data block with additional (header) bits. In the figure, the abbreviations have the meaning given in the table: Abbreviation

Long name

Description

SB

Stealing Bits

Bits indicating the MCS used.

USF

Uplink State Flag

Indication, which subscriber can use the next uplink radio block

RLC/MAC header

Radio Link Control/ Medium Headers which define the data flow, Access Control header coding, puncturing, etc.

HCS

Header Check Sequence

Checksum for the header bits

FBI

Final Block Indicator

indicates the end of transmission

E

Extension bit

indicates whether additional (optional) octets are present in the RLC header

BCS

Block Check Sequence

Checksum for the data bits

TB

Tail bits

Data

As can be seen from the figure below, the protection of the USF and the RLC/MAC header is better than the protection of the payload.

46


Introduction

Siemens

3 bits USF

45 bits

612 bits

612 bits

RLC/MAC HCS FBI E Data = 592 bits BCS Hdr.

TB

Rate 1/3 convolutional coding 36 bits

135 bits

36 bits

124 bits

TB

Rate 1/3 convolutional coding

1836 bits

1836 bits

puncturing

puncturing SB = 8

FBI E Data = 592 bits BCS

puncturing

612 bits

612 bits

612 bits

612 bits

612 bits

612 bits

P1

P2

P3

P1

P2

P3

1392 bits

Fig. 18 Example of a two RLC data blocks mapped on one radio block using MCS9 coding scheme


47

Introduction

Siemens

5.3

E-GPRS link quality control

Link quality control is implemented by two different means:

• the mandatory link adaptation, and • the optional incremental redundancy.

5.3.1

Link adaptation

Link adaptation is based on measurements of the bit error rate. Depending on the number of bit errors a quality level is determined by the MS and reported to the base station system. The base station system decides, based on the quality level, whether or not a change of the coding scheme increases the performance, and informs the MS about the new coding scheme to be used. Link adaptation takes long-term fading effects into account and ensures the highest possible data transmission rate in this regard. An example of the achievable data rates in dependence of the MCS used and the Carrier/Interference Ratio is shown in the figure below (GSM 900, TU50, without frequency hopping).

5.3.2

Incremental redundancy

In addition to the link adaptation, another method of link quality control may be used in EGPRS: incremental redundancy. Incremental redundancy is a means to compensate short-term fading effects. It uses the fact that within one coding scheme different puncturing schemes are defined. If a data packet has been received but cannot be decoded successfully, the originator may transmit a different punctured version of the data packet in the same coding scheme. Receivers can operate in two different modes:

• Either the receiver discards the data block received in the first step and tries to decode the repeated data block, or

• the receiver will keep the first received data packet in its memory and combine it with the information received in the second step (joint decoding).

Joint detection must be implemented in EGPRS mobiles, for base station systems it is an optional solution.

48


Introduction

Siemens

Throughput in kbit/s 60

MCS-9 (A) MCS-8 (A)

50

MCS-7 (B)

40 30

MCS-6 (A) MCS-5 (B) MCS-4 (C) MCS-3 (A) MCS-2 (B) MCS-1 (C)

20 10 0

5

15

10

25

20

30

C/I in dB

Fig. 19 Throughput of the 9 different E-GPRS modulation and coding schemes as function of C/I

MCS-2

MCS-3 Family A

37 octets

37 octets

37 octets

37 octets

Family B

28 octets

28 octets

28 octets

28 octets

MCS-5

MCS-6

MCS-7

MCS-9 MCS-3 MCS-1

34+3 octets 34+3 octets Family A padding

Family C

MCS-6

22 octets

22 octets

MCS-4 34 octets

34 octets

34 octets

34 octets

MCS-8

Fig. 20 Grouping of the modulation and coding schemes of E-GPRS into different families


49

Introduction

Siemens

5.4 5.4.1

Packet data channels Logical channels - use of "classical" logical channels for GSM-CS

A logical channel is used for a special purpose / contents. For example the MSs have to find out if this cell is a suitable one, which features are offered (e.g. HR/FR/EFR, GPRS, ...), what is the structure of Um (channel combination), ... This is provided by the BCCH which is only transmitted in the downlink. Some resources have to be given for initial access for the MS (RACH). For these reasons logical channels have been defined to fulfill all tasks which are necessary in a GSM network on the air interface. The GPRS subscribers will share the air interface with the circuit switched users. On the other hand the protocol structure of GPRS is different from "classical" GSM-CS. Therefore the user traffic and (part of) the signaling will have to be separated. Before this separation can take place the different MS (GPRS/non-GPRS) have to be handled by signaling procedures for access (channel assignment). There are two solution of this problem. The first one is to use (some of) the logical channels for GSM-CS: The GPRS-MS detects the BCCH of this particular cell and looks for the system information to find out if GPRS is available. If this is a cell belonging to the same routing area the MS can choose this cell and wait for paging or for the user to use the RACH for activating a PDP. In case that the user wants to run an PS application the GPRS MS will use an access burst (RACH) which indicates that this is a GPRS MS and the request will be answered by the PCU assigning resources for packet switched traffic (time slots reserved for GPRS). Signaling (e.g. for authentication) will then take place using these resources indicated by the message in the AGCH. So GPRS uses some of the logical channels of GSM-CS. On one hand this can be an advantage if the resources are sufficient. On the other hand if in the future more and more GPRS traffic has to be handled, separate logical channels reserved for GPRS MS will have to be given. This is the second solution. In any case the GPRS MS will have to look for the BCCH of the cell to find out whether or not GPRS is available. If the second solution has been chosen the GPRS MS will also read information where a PBCCH (Packet Broadcast Control Channel) is to be found (which time slot). This second solution will be explained below.

50


Introduction

Siemens

Logical channels (for circuit switched GSM) BCCH

BCH Broadcast Channel

Broadcast Control Channel

DL

FCCH Frequency Correction Channel

Signaling

Common Control Channel

Frequency synchronization

SCH

Time synchronization (TDMA-No.+BSIC)

PCH

Paging / Searching (MTC)

Synchronization Channel

Paging Channel

CCCH

CGI, FR/EFR/HR, GPRS available frequency hopping, channel combination,...)

NCH

DL

Notification Channel

UL

Access Grant Channel

Paging (PtM connection)

AGCH

Allocation of dedicated signaling channel

RACH

Request for access

SDCCH

Dedicated signaling MS ↔ BTSE (Call Setup, LUP, Security, SMS, CBCH,...)

Random Access Channel

DCCH Dedicated Control Channel

UL + DL

Stand Alone Dedicated Control Channel

SACCH

Slow Associated Control Channel

FACCH

Fast Associated Control Channel

Traffic User Data

UL + DL

Measurement Report, TA, PC, cell parameters,... Signalling instead of TCH

TCH/F

User traffic (Full Rate)

TCH/H

User traffic (Half Rate)

Traffic Channe/Fl

Traffic Channel/H

Fig. 21 Logical channels for circuit switched GSM


51

Introduction

Siemens

5.4.2

Use of new logical channels for GPRS/E-GPRS

In addition to the existing logical radio channels used for signaling (BCCH, SCH, FCCH, PCH, RACH, AGCH, NCH as well as SDCCH, SACCH and FACCH) and the Traffic Channel (TCH) for circuit switched user information, a new set of logical channels was defined for GPRS. Packet traffic is realized by means of the Packet Traffic Channel (PTCH) which includes the following :

• Packet Data Traffic Channel PDTCH. • Packet Associated Control Channel PACCH The PDTCH is temporarily assigned to the mobile stations MS. Via the PDTCH, user data (point-to-point or point-to-multipoint) or GPRS mobility management and session management GMM/SM signaling information is transmitted. The PACCH was defined for the transmission of signaling (low level signaling) to a dedicated GPRS-MS. It carries information related to data confirmation, resource allocation and exchange of power control information. New GPRS signaling channels are mainly specified analogously to GSM Phase1/2. The Packet Common Control Channel PCCCH has been newly defined. It consists of a set of logical channels which are used for common control signaling to start the connection set-up:

• Packet Random Access Channel PRACH • Packet Paging Channel PPCH • Packet Access Grant Channel PAGCH • Packet Notification Channel PNCH PRACH and PAGCH fulfill GPRS-MS functions which are analogue to the “classical” logical channels RACH and AGCH for non-GPRS-users. The PNCH is used for the initiation of point-to-multipoint multicast (PtM multicast). For the transmission of system information to the GPRS mobile stations, the

• Packet Broadcast Control Channel PBCCH was defined analogue to the “classical” BCCH. In a physical channel all different types of logical channels can be contained (no separation into traffic and signaling channels respectively as is done in conventional GSM). The differentiation of channel contents is carried out per radio block using the MAC header, i.e. contents are specified for the four normal bursts of a radio block sent in each case. The MAC function, which distributes the physical channel to the various mobile stations and allocates radio resources to a MS can also use the conventional logical channels in GSM.

52


Introduction

Siemens

Broadcast channel DL

PBCCH Packet Broadcast Control Channel

Packet Signaling

Common Control channels

UL

PRACH

Access request for UL packet data transmission

PPCH

Paging GPRS-MS (PtP)

PNCH

Paging GPRS-MS (PtM)

Packet Random Access Channel

Packet Paging Channel

DL

Packet Notification Channel

PAGCH

Packet Access Grant Channel

PACCH UL&DL Dedicated channels UL DL

Packet Traffic

UL&DL

Packet System Information

Packet Associated Control Channel

Resource allocation

Dedicated signaling MS-network, e.g.power control

PTCCH/U

Packet Timing Advance Control Timing advance Determination and Channel Uplink/Downlink Control

PTCCH/D PDTCH

Packet Data Traffic Channel

Transmission of User data

Fig. 22 Logical channels for GPRS/E-GPRS

5.4.3

Channel combinations

The following type of channel combination support either packet data or packet data together with signaling related to packet data: 1. PBCCH+PCCCH+PDTCH/F+PACCH/F+PTCCH/F 2. PCCCH+PDTCH/F+PACCH/F+PTCCH/F 3. PDTCH/F+PACCH/F+PTCCH/F with PCCCH=PPCH+PRACH+PAGCH+PNCH.


53

Introduction

Siemens

5.5

Multiframe structure in GPRS/E-GPRS

The GPRS packet data traffic is arranged in 52-type multiframes (GSM Rec. 03.64). 52 TDMA frames in each case are combined to form one GPRS traffic channel multiframe which is subdivided into 12 blocks with 4 TDMA frames each. One block (B0-B11) contains one radio block each (4 normal bursts, which are related to each other by means of convolutional coding). Every thirteenth TDMA frame is idle. The idles frames are used by the MS to be able to determine the various base station identity codes BSIC, to carry out timing advance updates procedures or interference measurements for the realization of power control. For packet common control channels PCCH, conventional 51-type multiframes can be used for signaling or 52-type multiframes. The GPRS users can use "classical" common control channels of GSM before they will be directed onto their PTCHs. The BCCH will be read by all mobiles anyway. Either in case of GSM mobiles to fulfill the same tasks as before and for GPRS equipment this logical channel will indicate weather GPRS service is available and if extra logical channels (PBCCH, PPCH, ...) are used. GSM CS traffic and GPRS subscribers are clearly separated so that there is no conflict due to different signaling or multiframe structure. It is important that there are no "visible" changes for "GSM only mobiles" due to the introduction of GPRS. GSM CS connections will use for example the same 26 multiframe structure for TCH and the 51 multiframe structure for signaling.

54


Introduction

Siemens

Multiframe for GPRS/E-GPRS

• PDCH follows 52 multiframe structure • 52 Multiframe: 12 Blocks à 4 TDMA-frames + 4 idle frames

52 TDMA Frames = PDCH Multiframe 4 TDMA Frames

1 TDMA Frame

B0 B1 B2 T B3 B4 B5 i B6 B7 B8 T B9 B10 B11 i B0 - B11 = Radio Blocks (Data / Signaling) T = Frame used for PTCCH i = Idle frame

i (and also T) is used by the MS for: • Identification of BSICs • Signal Measurements

• BCCH indicates PDCH with PBCCH (in B0) • DL: this PDCH bears PDCCH & PBCCH PBCCH in B0 (+ max. 3 further blocks; indicated in B0) PBCCH indicates PCCCH blocks & further PDCHs with PCCCH • UL: PDCH with PCCCH: all blocks to be used for PRACH, PDTCH, PACCH PDCH without PCCCH: PDTCH & PACCH only Fig. 23 Multiframe structure for PDCH


55

Siemens

56

Introduction


Introduction

6

Siemens

Hardware impacts of GPRS/E-GPRS on SBS


57

Introduction

Siemens

t

6.1

Affected modules in the BTSE and BSC

In the BTSE hardware no special modules are necessary for GPRS. E-GPRS, however, requires an EDGE-capable Carrier Unit, the so-called E-CU. The E-GPRS coding schemes are supported by the BTSE software without any modification of modules. For the BSC, the PCU must be inserted. The functions of the PCUs supporting the interworking of packet data between the Abis and Gb interfaces may be divided as follows: Channel handling via the Abis interface Implementation of the BSS GPRS protocol and the network service (frame relay) functions on the Gb interface. The number of PCU modules is dependent on the required capacity. For the high-capacity BSC step 1, one up to 6 modules termed PPXX handle the GPRS/E-GPRS traffic. These modules work load-sharing and distribute the traffic evenly to all processor cards of one pool. The capacity of a PPXX is limited to File 1 256 physical channels, i.e. 4 Mbit/s throughput (if the backplane of the traditional BSC is used) File 2 320 physical channels, i.e. 5 Mbit/s throughput (if a new backplane for the BSC is used, in future release) So a total amount of 1536 PDTCH or 24 Mbit/s is available at present time (without redundant module).

58


Introduction

Siemens

• 6 PPXU for GPRS service • 2 PPXL for LAPD & SS7 • 9+2 QTLP • 1280 PDTCH Guaranteed 1536 as possible maximum • 255 EDGE Channels @ MCS9 306 as possible maximum • 20 Mb/s (Abis) packet bandwidth guaranteed 24 Mb/s as possible maximum • 248 (LAPD + SS7L) • 256 PDTCH/PPXU • 72 PCM ports as PCMS, PCMB and PCMG

Fig. 24 Rack layout of high capacity BSC/72 together with capacity figures


59

Introduction

Siemens

In the high-capacity BSC step 2, up to 12 PPXX can be mounted. Corresponding capacity figures are summed up in the following table and shown in the figure below. BSC/72

BSC/72

BSC/120

BSC/120

TDPCv6

TDPCv9

TDPCv6

TDPCv9

MPCCv7

MPCCv9

MPCCv7

MPCCv9

Controlled TRX

500

500

500

900

Controlled Cells

250

250

250

400

Controlled BTSE

200

200

200

200

Controlled TRAU

32

36

36

48

Controlled SS7L

16

16

16

16

PCM lines (Abis + Asub + Gb)

72

72

120

120

LAPD (Abis + Asub)

240

240

240

240

GPRS Channels

1536

1536

1536

3072

Capacity (Erl.)

3200

3200

3200

4800

Functionality

Note: E-GPRS is restricted to BTS+ platform and is not supported by the traditional BTS.

60


Introduction

Siemens

• 12 PPXU for GPRS service • 2 PPXL for LAPD & SS7 • (7+1) + (3+1) STLP • 2816 PDTCH Guaranteed and 3072 as maximum • 560 EDGE Channels @ MCS9 612 as maximum • 44 Mb/s Abis packet bandwidth guaranteed and 48Mb/s as maximum • 248 LAPD + SS7L • 256 PDTCH/PPXU • 120 PCM ports as PCMS + PCMB + PCMG

Fig. 25 Rack layout of high capacity BSC/120 together with capacity figures


61

Siemens

62

Introduction


Introduction

7

Siemens

Exercise


63

Siemens

64

Introduction


Introduction

Siemens

Exercise Title:

Principal understanding of GPRS

Objectives:

Repetition of GPRS basics

Pre-requisite:

GPRS basic knowledge

Query What are the main functions of the MAC protocol? Can a physical timeslot on air interface be shared by 1. several subscribers for circuit-switched GSM? 2. several subscribers for GPRS? 3. several subscribers for E-GPRS? 4. several subscribers for GPRS and E-GPRS? 5. several subscribers for circuit-switched and for GPRS services? Can a GPRS/E-GPRS MS know in advance, whether or not a received block 1. will contain information for itself or for any other MS? 2. will contain signaling or data as information?


65

Siemens

66

Introduction


Introduction

8

Siemens

Solution


67

Siemens

68

Introduction


Introduction

Siemens

Solution Title:

Principal understanding of GPRS

Objectives:

Repetition of GPRS basics

Pre-requisite:

GPRS basic knowledge

Query What are the main functions of the MAC protocol? The MAC realizes: 1. medium access 2. medium sharing 3. medium release Can a physical timeslot on air interface be shared by 1. several subscribers for circuit-switched GSM? Yes (up to two in case of halfrate). 2. several subscribers for GPRS? Yes (up to 16 subscribers max.). 3. several subscribers for E-GPRS? Yes (up to 16 subscribers max.). 4. several subscribers for GPRS and E-GPRS? Yes (up to 16 subscribers max.). 5. several subscribers for circuit-switched and for GPRS services? Yes. Can a GPRS/E-GPRS MS know in advance, whether or not a received block 1. will contain information for itself or for any other MS? No. 2. will contain signaling or data as information? No.


69

Siemens

70

Introduction


01 Mn1889eu11mn 0001 Introduction

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