PART 5 GSM – Switching & Mobility Lecture 5.1 Protocol architecture overview
Giuseppe Bianchi
The GSM network layer Î Divided in three sub-layers Ö Radio Resource Management (RR) ÆProvides a communication link between MS and MSC;
Ö Mobility Management (MM) ÆManages DB for MS location
Ö Communication Management (CM) ÆControls user connection
Î Underlying base: Ö Transmission level
CM MM RR Transmission
Giuseppe Bianchi
1
RR Î Manages administration of frequencies and channels Ö Mostly deals with air interface ÆSeveral RR functions considered in previous part
Î Guarantees stable link upon handover ÆSurprise! handover is part of RR, not MM!
Î Function summary: Ö Monitoring BCCH, PCH Ö RACH administration Ö Request/assignment of channels Ö MS power control & synchronization Ö Handover Î Where is RR: Ö MS, BTS, BSC, MSC Giuseppe Bianchi
MM Î Manages user location and tasks resulting from mobility Î Function summary: Ö TMSI assignment Ö MS localization Ö Location updating Ö MS authentication Ö MS identification, attach/detach Î Where is MM: Ö MS, MSC
Giuseppe Bianchi
2
CM Î Controls calls, supplementary services, and SMS Î Function summary: Ö Call establishment (from MS, to MS) Ö Emergency call management Ö Call termination Ö DTMF signaling (Dual Tone MultiFrequency) Ö In-call modification Î Where is CM: Ö MS, MSC, GMSC
Giuseppe Bianchi
Protocol placement CM GMSC
MM HLR
RR Trans. MS
BTS
BSC
MSC (VLR)
Giuseppe Bianchi
3
Protocol outline MS
BTS
Relay MSC
BSC
CM
RIL3-CC
MM
RIL3-MM
RR
RIL3-RR
RSM
Anchor MSC
HLR
MAP/D
BSSMAP
MAP/E TCAP
LAPDm
LAPD
RIL3: Radio Interface Layer 3 RSM: Radio Subsystem Management BSSMAP: BSS Management Application Part MAP: Mobile Application Part
SCCP MTP
SCCP MTP
SCCP MTP
TCAP: Transaction Capabilities Application Part SCCP: Signaling Connection Control Part MTP: Message Transfer Part LAPD: Link access Protocol on D channel LAPDm: Link access Protocol on Dm channel
Giuseppe Bianchi
PART 5 GSM – Switching & Mobility Lecture 5.2 handover (physical mobility)
Giuseppe Bianchi
4
Neighbor cells BTS 2
BTS 1
BTS n
Î A station must: Ö monitor beacon power level of neighbor cells Ö Keep detailed track of best 6 neighbor cells Ö DECODE their BCCH (i.e. read FCCH, SCH) to get parameters ÆAt least once every 5 minutes ÆBSIC (from SCH) refreshed every at most 30s Giuseppe Bianchi
Camping cell selection path loss criterion C1
Select cell with greatest c1(n)>0:
C1(n) = RXLEV(n) − − RXLEV_ACCESS_MIN −
− max[0, (MS_TXPWR_MAX_CCH − P )]
Î RXLEV(n): received power from BTS(n) Î RXLEV_ACCESS_MIN: minimum received power level required for registration in the cell Î (parameter transmitted on BCCH; typically –98 to –106 dB) Î MS_TXPWR_MAX_CCH: maximum allowed transmitted power on RACH Î (parameter transmitted on BCCH; typically 31-39 dBm) Î P: maximum MS power (from MT class)
When cell parameters are the same, simply select cell with higher RXLEV! Giuseppe Bianchi
5
Cell reselection criterion (C2) ÎReselect cell with greatest C2>0:
C2(n) = C1(n) + CELL_RESELECT_OFFSET − − TEMPORARY_OFFSET × H(PENALTY_TIME − T) ⎧0 x < 0 where H(x) = ⎨ ⎩1 x ≥ 0 Î T: amount of consecutive time since considered cell became with C1>0 Î PENALTY_TIME, CELL_RESELECT_OFFSET, TEMPORARY_OFFSET: BCCH parameters Î If all parameters = 0, reselect cell with better path loss performance (no time hysteresis included)
Giuseppe Bianchi
Consequences of cell reselection
BTS
BTS
Î None, when MS idle! ÆNo need to inform BTS at all!
Î Exception: Ö When cell reselection implies a Location Area Update ÆNeed to inform the network!
Î Additional restriction: Ö C2>CELL_RESELECT_HYSTERESIS Giuseppe Bianchi
6
handover Î Procedure in which an MS releases a connection with a BTS, and establishes a connection with a new BTS, while ensuring that the ongoing call is maintained Ö The MS remains in dedicated state (unlike cell reselection, where MS is in idle state) Î Handoff: synonymous of handover Î Needs two mechanisms Ö Handover preparation: detection of cell-border crossing ÆBased on radio link quality measurements
Ö Handover execution: setup of a new channel in a cell, and tear-down of a previous channel Î Improved handover mechanisms: Ö Seamless handover: when active call performance is not impaired ÆNot possible in GSM: for about 100-200ms, communication is interrupted
Ö Soft Handover: when two channels are simultaneously set-up (old and new) ÆNot possible in GSM; possible in UMTS
Giuseppe Bianchi
Hard, Seamless, Soft handover Hard handover (GSM)
before
during
after
MSC
MSC
MSC
BSS 1 f1
BSS 2
BSS 1 f1
MS MSC
Seamless (DECT)
BSS 1 f1
Soft handover (UMTS)
BSS 2
BSS 1 f1
MS
f1
MSC
BSS 2
BSS 2 f2
MS MSC
BSS 2 MS
BSS 1
f2
MS
BSS 1 f1
f2
MSC
MSC
BSS 2
BSS 2 MS
BSS 1
MSC
BSS 1
MS
f1
MS
BSS 2
f1
BSS 1
BSS 2 MS
f1
Giuseppe Bianchi
7
Handover classification Classification by motivation Î Rescue handover
(mandatory handover)
Ö Driven by radio channel quality degradation Î Confinement handover
Classification by typology Î Internal handover Ö Intra-BTS ÆNew radio channel in the same cell ÆNot termed as “handover” but as“subsequent assignment”
(network-directed handover)
Ö Target: minimize radio interference Ö Assign new channel when old channel results critical for total interference Î Traffic handover
Ö Inter-BTS (Intra-BSC) ÆUnder control of same BSC
Î External handover Ö Inter-BSC (Intra-MSC) ÆChange reference BSC; may imply a location area update
(network-directed handover)
Ö Driven by traffic congestion conditions Ö Also called load-balancing
Ö Inter-MSC ÆMost complex: need to change MSC
Giuseppe Bianchi
Types of handover Switching point for all inter-MSC handover Switching point for internal handover
Anchor MSC: the MSC that first managed the current call
Relay MSC: the MSC that currently manages the call
A-MSC
R-MSC
A BSC
BSC
Switching point for inter-BSC handover
BSC
A-bis BTS
BTS
BTS
BTS
radio interface
Giuseppe Bianchi
8
Handover taxonomy Î BCHO: Base station Controlled Handover Ö Handover detection: BS Ö Handover Execution: BS Î MCHO: Mobile Controlled Handover Ö Handover detection: MS Ö Handover Execution: MS Î MAHO: Mobile Assisted Handover Ö Handover detection: MS Ö Handover Execution: BS Î GSM: somehow a BCHO with a flavor of MAHO Ö Handover decision always taken by BSC Ö Based on measures taken at both BTS and MS Ö New channel selection decision taken at BSC or R-MSC or A-MSC (depending on handover type) based on traffic consideration Giuseppe Bianchi
Handover preparation Î Measurements performed at BTS Ö Up-link signal level received from MS lower than threshold ÆRXLEV_UL < L_RXLEV_UL_H
Ö Up-link signal quality (BER) received from MS ÆRXQUAL_UL < L_RXQUAL_UL_H
Ö Distance between MS and BTS Æadaptive timing advance parameter > MAX_MS_RANGE
Ö Interference level in unallocated time slots. Î Measurements performed at MS. Ö Down-link signal level received from serving cell ÆRXLEV_DL < L_RXLEV_DL_H
Ö Down-link signal quality (BER) received from serving cell ÆRXQUAL_DL < L_RXQUAL_DL_H
Ö Down-link signal level received from n-th neighbor cell ÆRXLEV_NCELL(n) > RXLEV_MIN(n)
RX signal level
From (dBm)
To (dBm)
RXLEV_0
-
-110
RXLEV_1
-110
-109
RXLEV_2
-109
-108
RXLEV_3
-108
-107
…
…
…
…
…
…
RXLEV_62
-49
-48
RXLEV_63
-48
-
Bit error Ratio
From (%)
To (%)
RXQUAL_0
-
0.2
RXQUAL_1
0.2
0.4
RXQUAL_2
0.4
0.8
RXQUAL_3
0.8
1.6
RXQUAL_4
1.6
3.2
RXQUAL_5
3.2
6.4
RXQUAL_6
6.4
12.8
RXQUAL_7
12.8
-
Giuseppe Bianchi
9
A note on MS distance ÎDistance can be measured based on TA ÎTA = advance bits ÖIdeally, TA should be set as
TA[bits ]⋅ tbit =
2d c
⇒ d=
TA ⋅ c ⋅ tbit 2
ÖHence, the TA resolution, in mt, is:
d (TA) = TA
c ⋅ tbit = TA 2
300000[mt / ms] ⋅ 2
1 [ms ] 270.833 ≈ TA ⋅ 554mt
ÖINSUFFICIENT for microcells! ÖSufficient only to understand we are going out of the cell Giuseppe Bianchi
Handover preparation – additional metrics Î Transmission power Ö Maximum MS transmission power Ö Maximum serving BTS transmission power Ö Maximum neighboring BTSs transmission power Î congestion status Ö of serving BTS Ö of neighboring BTSs Æ provided they can support the MS.
Î Handover Margin Ö To avoid ping-pong handover effect Ö 5-10 dB in normal operation; up to 30dB in urban operation (to fight shadowing)
RXLEV (cell A)
RXLEV (cell A)
HANDOVER ALGORITHM: operator-dependent! GSM standard SUGGESTS a simple reference algorithm, but implementation left to operator
Handover
Handover
RXLEV (cell B)
RXLEV (cell B)
hysteresis
Giuseppe Bianchi
10
handover procedure skeleton 1) Handover request goes up to switching point MSC
2) Switching point prepares new path on fixed net 3) Switching point sends HO command to MS
2
1 5
4) MS accesses new channel
BSC
BSC
5) Old channel/path torn down
3 4 BTS
BTS
Giuseppe Bianchi
Signaling for intra-MSC handover (simplified)
MS
BTS-A Measurement info
handover command
BSC-A
MSC
handover required (destination cell)
BSC-B
handover request
handover req. ack (contains handover handover command command message prepared by BSC-B with info on BCCH, channel assigned, etc)
BTS-B
MS
Channel allocation Channel activation ACK
handover access (an access burst on new TCH!!!) physical info (new TA, power) handover complete
handover detection handover detection
handover complete clear command clear complete
Measurement info
Giuseppe Bianchi
11
Inter-MSC handover Î More complex, as an ISDN circuit must be set between MSCs Ö We’ll not enter into details (just the basic ideas) Î Two cases Second MSC change (subsequent handover)
First MSC change (basic handover)
MSC-A
X
MSC-A
MSC-R1
Note the role of the Anchor MSC!
X
MSC-R1
MSC-R2
X
Giuseppe Bianchi
PART 5 GSM – Switching & Mobility Lecture 5.3 location registration/update Authentication & Ciphering
Giuseppe Bianchi
12
Location Area vs MSC service area
LA-1
LA-2
MSC LA-4
LA-3
VLR …
LA-n
Giuseppe Bianchi
Registration vs update Î Very similar procedures, with goals: Ö Determine where the user is Ö Authenticate user Î Differences: Ö Location Registration ÆUser first access to PLMN » Needs to send IMSI and receive TMSI
Ö Location Update ÆSubsequent accesses to PLMN (either in old or new MSC/VLS) » Also after MS shut-down! » TMSI-based identification
Î Registered user: Ö The PLMN knows the LA where the user is (or is supposed to be)
Giuseppe Bianchi
13
Procedure start-up ÎMS switches on ÎDetects BCCH carrier ÖTune and synchronize ÎListens to BCCH ÎObtains Location Area Identifier ÖLAI: [CC,MNC,LAC] ÆCountry Code (CC): 3 digits ÆMobile Network Code: 2 digits ÆLocation Area Code: max 5 digits Giuseppe Bianchi
LR/LU (very) basic idea MSC
3
VLR
HLR
BSC
BTS 1
2
BTS BTS
1) Obtain LAI from BCCH 2) Register MS ID into local VLR 3) Update pointer at HLR
MS
Giuseppe Bianchi
14
Location Registration MS
BSS/MSC
Loc. Upd. Request IMSI, LAI
VLR
Update Loc. Area IMSI, LAI
HLR Auth. Param. Req. IMSI Auth. Info (Auth. Parameters)
AUC
Auth. Info. Req. IMSI Auth. Info (Auth. Parameters)
authentication Update Location IMSI, MSRN Start Ciphering Insert Subscrib. Data Kc Forward new TMSI IMSI, additional data TMSI Insert Subscrib. Data ACK Locat. Upd. Accept Locat. Upd. Accept IMSI
Activate ciphering
TMSI Realloc Cmd Locat. Upd. Accept TMSI Realloc ACK
TMSI ACK
Giuseppe Bianchi
Authentication (managed by VLR)
IMSI, RAND
Authentication Request
MS Ki
SRES, Kc
RAND A3
SRES
SRES
Authentication Response Signed RESult: 32 bit SRES
Ki
VLR
Challenge: 128 bit RAND
HLR / AUC
Equal?
RAND A8 Kc Giuseppe Bianchi
15
Authentication (details) Î Side effect of authentication: Ö Generate encryption key Kc via A8 algorithm Î Secret A3, A8 algorithms (one-way hash functions) Ö Stored into the SIM ÆAlong with secret key Ki
Ö Note that roaming operator DOES NOT need to know them! ÆSince A3,A8 run ONLY in the AUC at the home HLR ÆKi is NEVER transmitted away from AUC or MS!
Î Generally implemented together Ö [SRES,Kc] = A38[Ki,RAND] Î To reduce signaling, real implementation slightly different: Ö VLR sends IMSI Ö Receives back several tuples of (RAND, SRES, Kc) to be used for the considered MS also in subsequent accesses Giuseppe Bianchi
ciphering Î A5 algorithm is known (to allow roaming) Î Generates two ciphering sequences Ö one for uplink, one for downlink Ö Sequence periodic with period 26x51x2048=2,715,648 Æ 221=2,097,152 < 2,715,648 < 222=4,194,304
Î 114 bits per frame, depending on frame number Î XOR-ed with burst data field
Frame number FN, 22 bits
MS
Kc 64 bits
Frame number FN, 22 bits
A5
BTS
A5
S1 In-clear uplink
Kc 64 bits
S1
S2
XOR
In-clear downlink XOR
XOR
enciphered uplink enciphered downlink
S2
XOR
In-clear uplink
In-clear downlink
Giuseppe Bianchi
16
Location Update in same VLR MS
(same as location registration, but with TMSI) BSS/MSC VLR HLR
Loc. Upd. Request TMSI, LAI
AUC
Update Loc. Area TMSI, LAI
authentication
Update Location IMSI, MSRN Generate New TMSI
Start Ciphering Kc Insert Subscrib. Data Forward new TMSI IMSI, additional data Ins. subs. data ACK
Activate ciphering
Locat. Upd. Accept TMSI Realloc Cmd
Locat. Upd. Accept IMSI
Locat. Upd. Accept TMSI Realloc ACK
TMSI ACK Auth. Param. Req. IMSI Auth. Info N x (Kc,RAND,SRES)
Auth. Info. Req. IMSI Auth. Info N x (Kc,RAND,SRES)
Giuseppe Bianchi
Changing MSC/VLR HLR VLR
MSC
Public Publicswitched switched telephone telephonenetwork network PSTN PSTN
VLR
MSC
Base Station Base Station
An MS always has a dedicated entry in the HLR Plus one entry in JUST 1 VLR (related to the MSC the user is connected to) Giuseppe Bianchi
17
TMSI ÎTMSI = Temporary Mobile Subscriber Identity Ö4 octets (32 bits) Operator may set a 6min up to 24hrs periodicity ÖRenewed periodically; at every LU / IMSI_attach for LU (value transmitted ÆVia TMSI_Reallocation_Command/TMSI_Reallocation_Complete ÆRATIONALE: renew TMSI when transmitted in clear! (TMSI reallocation occurs in ciphering mode)
ÎMeaningful only in a given VLR ÖSpecifically, only for a given Location Area!!
on BCCH) IMSI_attach = a special LU in a same Location Area; IMSI_attach follows an IMSI_detach (power-down of MS)
ÆSome author (Mouly-Pautet) uses the term » TIC (Temporary Identity Code) = 4 bytes » TMSI = TIC+LAI = unambiguous user identification
ÎWhile entering a new Location Area: Ö user must identify itself with TMSI+LAI pair. Giuseppe Bianchi
Location Update: different VLR MS
BSS/MSC
Loc. Upd. Request TMSI(+ old LAI), LAI
VLR-new
HLR
VLR-old
Update Loc. Area TMSI(+ old LAI), LAI determine VLR-old From old LAI Send parameters (TMSI, old LAI)
IMSI response (IMSI,RAND,SRES,Kc)
authentication Update Location IMSI, MSRN Generate New TMSI
Activate ciphering …
Cancel Location IMSI Cancel Locat. ACK
Start Ciphering Kc Insert Subscrib. Data Forward new TMSI IMSI, additional data Ins. subs. data ACK …
Locat. Upd. Accept IMSI
Giuseppe Bianchi
18
Special cases 1. New VLR not capable of determining old VLR from old LAI 2. Old VLR does not recognize TMSI MS
Ö Identification procedure Æ
IMSI transmitted in clear
MSC Identity Request Identity Response IMSI
PAGING: - Normally based on TMSI - But when no valid TMSI information available (e.g. after a DB restore after crash), based on IMSI
Giuseppe Bianchi
PART 5 GSM – Switching & Mobility Lecture 5.4 Call Management & routing
Giuseppe Bianchi
19
Notation ÎA call involves two “Parties” ÎCalling Party (caller) Öuser generating the call ÎCalled Party (callee) Öuser receiving the call ÎMobile Originating Call (MOC) ÖCall originated by an MS ÎMobile Terminating Call (MTC) ÖCall directed to an MS Giuseppe Bianchi
Call establishment basics MS
Mobile Terminated Call Fixed MSC party setup
setup
Mobile Originated Call MS
setup
Call proceeding
Call confirmed alerting connect
connect
Connect
Connect Connect Ack
DATA
DATA In ISDN ISUP:
setup alerting
alerting alerting
Fixed party
MSC
- setup = IAM - Alerting = ACM - Connect = ANS
(Initial Address Message); (Address Complete Message); (Answer)
Giuseppe Bianchi
20
Call establishment steps MS
Mobile Terminated Call
network
MS
Mobile Originated Call
network
Paging request Channel request
Channel request
Immediate Assignment
Immediate Assignment
Service Request
Paging Response
Authentication Request
Authentication Request
Authentication Response
Authentication Response
Ciphering mode command
Ciphering mode command
Ciphering Mode Complete
Ciphering Mode Complete Setup
Setup Call proceeding
Call Confirmed Assignment Command Assignment Complete
Assignment Command Assignment Complete Alerting
Alerting
Connect
Connect Connect Acknowledge
Connect Acknowledge
Giuseppe Bianchi
Radio Resource allocation three standardized solutions
Î Non-Off Air Call Set-Up (Non-OACSU) Ö Normally used (previous description) Î Off Air Call Set-Up (OACSU) Ö TCH assigned only when the called party actually responds! ÆBest utilization of radio resource (avoids allocation if callee not available) ÆCall drop if no TCH is available at this point
Î Very Early Assignment (VEA) Ö Immediate assignment of TCH ÆFastest signalling process ÆWaste of resources
VEA RACH Non-OACSU RACH OACSU RACH
TCH (FACCH) TCH (DATA) SDCCH TCH (FACCH) TCH (DATA) SDCCH TCH (DATA) Connection established
Callee responds
Giuseppe Bianchi
21
DTMF signaling Î Dual-Tone Multi-Frequency Ö Digital tones associated to terminal keys Æ‘0’…’9’…’#’…
Î Inband signalling Ö transmitted in the traffic channels! Ö Not in the signalling network MS MSC Start DTMF (w. key code) Start DTMF ACK
Key Pressed
On air interface: Ö Signal trasmitted on FACCH as signalling data (code of pressed key) Ö Otherwise coded compression would distort DTMF tones Ö Tone generated at MSC when STOP DMTF message received
On FACCH)
Stop DTMF
Giuseppe Bianchi
1: M SI S
ISDN
PLMN 4: M SR N
GMSC
5: MSRN VLRB
MSCB ng gi pa 7:
6: TMSI
N SD SI SRN M 2: 3: M
MSCC
D N
Routing an MTC
MSCA
HLR
Giuseppe Bianchi
22
Routing an MTC (alternative) During an LU within a same VLR, MSRN is NOT signaled!
ISDN
1: M SI S
MSRN retrieved on a per-call basis! (choice of solution depends on trade-offs)
PLMN
GMSC 6: M SR N
N SD SI SRN M 2: 5: M
MSCC 7: MSRN VLRB
MSCB
HLR
MSCA
ng gi pa 9:
8: TMSI
D N
reduces signalling load during LU
3: IMSI 4: MSRN
Giuseppe Bianchi
Routing calls to Roaming MS ISDN (UK)
ISDN (ita)
International Switching Center
PLMN 2
MSC
(UK)
International Switching Center
Transit Exchange Local Exchange
GMSC 1 MSISDN +39.335.1234567
PLMN 1
MSRN +44.NDC.8877665
(ITA)
MSC
HLR 335.1234567
Giuseppe Bianchi
23
“tromboning”
Call to MSISDN +39.335.3043125
MSC ISC
PLMN 2
(UK)
(UK) Call to MSISDN +39.335.1234567
ISC (ITA)
GMSC 1
MSISDN +39.335.1234567
PLMN 1 (ITA)
MSRN +44.NDC.9876543
MSC
Is the PRICE (!) to pay for simple routing and billing
HLR
Giuseppe Bianchi
Tromboning technical solutions ÎFirst alternative: national-wise ÖAdd a new database - Roamer Location Cache (RLC) ÆConsulted by ISCs (which MUST support GSM-MAP!)
ÎSecond alternative: PLMN specific ÖRLC within the PLMN + associated switch ÖCaller must dial special NDC number (the switch!) ÆI.e. must know the MS is roaming in the PLMN…
ÖAdditional devices and protocol modifications required » Extensions toVLR or to GMSC » Details in “Lin-Chlamtac” Giuseppe Bianchi
24
RLC at ISC - Location Registration and call management RLC
3 bis
PLMN 2
ISC
VLR
2
(UK)
MSC
(UK)
1
3
PLMN 1 ISC (ITA)
4
HLR
(ITA)
Giuseppe Bianchi
Short Message Service ÎSMS: Ömessages up to 160 bytes ÖMessage concatenation allowed ÎTransmitted on air interface over: ÖSACCH (when user in conversation) ÖSDCCH (when user in idle state) ÎTwo transmission modes in a cell: ÖPoint-to-point Öcell broadcast ÎConnectionless service Ömessage switching (store&forward) ÖImplemented through the Short Message Service Center Giuseppe Bianchi
25
SMS routing management MSC
PLMN
Internet, PSDN
IWMSC Short Message Service Center
Get routing info for terminating MS
SMS-GMSC
HLR
PLMN MSC Giuseppe Bianchi
Protocol hierarchy MS Short Message Application Layer (SM-AL)
SM-SC
Short Message Transfer Protocol (SM-TP)
Short Message Transfer Layer (SM-TL)
MSC
IW-MSC
Short Message Relay Layer (SM-RL)
Short Message Short Message Relay Entity Short Message Relay Entity Relay Protocol (SMR) (SMR) (SM-RP) Connection Short Message Short Message Short Message Management Control Entity Control Protocol Control Entity Sublayer (CM-sub) (SMC) (SMC) (SM-CP)
Quite complex signalling involved (see specific texts) Giuseppe Bianchi
26
Number portability ÎSubscriber may switch operator without changing his number ÎFirst implemented in fixed network ÖRecently (may 2002) extended to mobile networks ÎEssential for fair competition among network operators ÖUK survey: 42% of corporate subscribers were willing to change mobile operator; but 96% were, if number could be ported ÎResistence from leading operators ÖNumber portability helps newer operators to compete with traditional ones Giuseppe Bianchi
Notation ÎDonor switch ÖThe switch corresponding to a “ported” telephone number ÎRecipient switch ÖThe switch to which the ported number is attached
Giuseppe Bianchi
27
Technical solutions a) call forwarding
Originating network
Donor network
switch
switch
switch Recipient network Originating switch sets-up trunk to donor switch Donor switch sets-up trunk to recipient switch Simplest solution, as call forwarding is a feature available in virtually all switches
But extremely inefficient routing and trunking resource consumption! Giuseppe Bianchi
Technical solutions b) query on release
Originating network
Donor network SS7 ISUP IAM
switch
switch SS7 ISUP REL
Number Portability DataBase
switch Recipient network
Donor switch “blocks” incoming call with a release message (REL) REL carries a QoR cause value, stating that called party number is ported Originating switch then queries Number Portability database Giuseppe Bianchi
28
Technical solutions c) all-call query
Originating network
Donor network
switch
Number Portability DataBase
switch
switch Recipient network
Originating switch queries Number Portability database for every call!! - best solution if majority of numbers are ported (no interaction with donor) - but very high DB load, as EVERY number must be looked-up! Giuseppe Bianchi
Mobile Number Portability Î Same ideas as fixed number portability Ö The donor switch is the GMSC of the donor network Î Donor GMSC Call forwarding (if more efficient fixed number portability not supported) Ö While porting number, may also get MSRN! Recipient network MSC
GMSC
MSRN
IRN
HLR
Note: If path must cross GMSC: Use Intermediate Routing Number
MSRN (or IRN)
Incoming call GMSC
Signaling relay function
HLR
Donor network Clearly, still suffers of tromboning! Giuseppe Bianchi
29
Mobile Number Portability (with all call query approach) approach)
Recipient network Query MSRN
MSC
GMSC
Return MSRN
HLR
IRN
Incoming call Query IRN
switch
Return IRN
Number Portability DataBase
Giuseppe Bianchi
Mobile Number Portability
improved – (with all call query approach) approach) Recipient network MSC
GMSC
HLR
MSRN Signaling relay function
Incoming call Query MSRN
switch
Return MSRN
Number Portability DataBase
Giuseppe Bianchi
30
