fresh field mtc 001 section 4

8/9/2019 Fresh Field Mtc 001 Section 4

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GSM SystemOverviewSection Four

Simple GSM Call Sequences

and Ladder Diagrams


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2001 Freshfield Communications Limited.Company Confidential Slide 2

Layer 3 MessagesLayer 3 Messages Call SequencesCall Sequences

Service Request and IMSI attach

Location Area Update

Authentication and Encryption

Mobile Terminated Calls

Mobile Originated Calls

Channel Release

Handover

SummarySummary

Presentation OutlinePresentation Outline


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At the end of this course, attendees will:At the end of this course, attendees will: Have an appreciation of call sequences in GSM

Have an appreciation of different types of handover

ObjectivesObjectives


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BSS MSCVLR

HLR

Call Control (CC)

Mobility Management (MM)

Radio Resource (RR)

BSS MSCVLR

HLR

BSS MSCVLR

HLR

Layer 3 MessagesLayer 3 Messages


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Grouped into three categoriesGrouped into three categories Call Control

Mobility Management

Radio Resource

To understand these categories, think of a mobile phoneTo understand these categories, think of a mobile phone

as being:as being:

A telephone

A mobile device A radio



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Call ControlCall Control Messages to and from the telephone part of phone

Responsible for setting up and clearing down calls

Messages pass between phone and MSC and are transparent

to the BSS

Mobility ManagementMobility Management

Concerned with mobility aspect of phone

Messages pass between phone and VLR and HLR

Messages are transparent to the BSS and MSC



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Radio ResourcesRadio Resources Messages are concerned with establishment, maintenance and

clearing down of radio links

Messages are exchanged between the phone and the BSS

In some equipment, messages may be transparent to the BTSand are instead all routed to the BSC.

In other equipment, some messages may stop at the BTS



8/23

2001 Freshfield Communications Limited.Company Confidential

Slide 8

Service Request and IMSI AttachService Request and IMSI Attach

MS MSC

SCCP Connection Request

BSSMAP Complete Layer 3 Information

SCCP Connection Confirm

(SDCCH) SABM Establishes the signalling link

(SDCCH) UA

(RACH) RIL3-RR Channel request

(AGCH - CCCH) RIL3-RR IMM Assignment - Move MS to SDCCH

BSS

BSS Transparent to MS


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Slide 9

Service Request and IMSI Attach (contd)Service Request and IMSI Attach (contd)MS

(SDCCH)

(SDCCH)

(SDCCH)

(SDCCH)

(SDCCH) UA

RIL3 - RR DISC

BSSMAP Clear Complete

IMSI Attach Ack

RIL3 -RR IMSI Attach Ack

BSSMAP Clear Cmd

RIL3 - RR Channel Release

UA

RIL3 -MM IMSI Attach

MAP/B Attach IMSI

MAP/B IMSI Attach Ack

BSS

(RACH)

(AGCH - CCCH)

(SDCCH)

(SDCCH)

RIL3 - RR Channel Request

RIL3 - RR IMM Assignment - Move MS to SDCCH

SABM Establishes the signalling link

MSC VLR


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Slide 10

Location Area UpdateLocation Area Update

MS BSS MSC VLR HLR

(RACH)

(AGCH - CCCH)

(SDCCH)

(SDCCH)

(SDCCH)

(SDCCH)

(SDCCH)


RIL3 - RR IMM Assignment - Move MS to SDCCH

SABM Establishes the signalling link

UA


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Slide 11

Location Area Update (contd)Location Area Update (contd)

MS BSS MSC VLR HLR

MAP/D Location

Update Result

MAP/B Location

Update Ack

RIL3-MM Location Update Accepted

RIL3-MM Location Update Reject

Unnumbered Acknowledgement

(SDCCH)

(SDCCH)

(SDCCH)

BSSMAP Clear Command

Channel release

Disconnect

BSSMAP Clear Complete


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Slide 12

Authentication and EncryptionAuthentication and Encryption

MS BSS MSC VLR HLR AUC

MAP/D Send Parameters

MAP/D Send Parameters Result - RAND, SRES, Kc

MAP/D Authenticate

RAND + CKSN RIL3 - MM Authentication Request

(SDCCH)

SRES + CKSN RIL3 - MM Authentication Response

(SDCCH) MAP/B Authentication Complete

(SDCCH) RIL3 - MM Service Accept

(SDCCH) RIL3 - MM Service Reject (if SRES's do not equal)

MAP/D Authentication Complete


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Slide 13

Authentication and Encryption (contd)Authentication and Encryption (contd)

MS BSS MSC VLR

MAP/B Set Cipher Mode

MAP/B Cipher Mode Command

(SDCCH) RIL3 - RR Cipher Mode Command

(SDCCH) RIL3 - RR Cipher Mode Complete - Encrypted

BSSMAP Cipher Mode Complete


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Slide 14

Optional

Mobile Terminated CallsMobile Terminated Calls

MS

UA

Encryption Process

(RACH)

(PCH - CCCH)

RIL3 - RR IMM Assignment(AGCH - CCCH)

RIL3 - RR Paging Response

(SDCCH)

(SDCCH)

RIL3 - RR Paging Request

BSS MSC VLR

MAP/B Send Info

LAI & TMSI

MAP/B Complete Call

LAI & TMSI

Request - TMSI

BSSMAP - Page TMSI


Paging Response

MAP/B - Process Access


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Slide 15

Mobile Terminated Calls (contd)Mobile Terminated Calls (contd)

MS BSS MSC VLR

(SDCCH) RIL3 - CC Call Setup

(SDCCH) RIL3 - CC Call Confirmation

(SDCCH) RIL3 - CC Alerting

Channel Assign Comd

(SDCCH)

(SDCCH) Channel Assign Complete

(FACCH - TCH) RIL3 - RR Alert

MS Rings

(FACCH - TCH) RIL3 - RR Connect

MS Answers

RIL3 - CC Connect Acknowledge

Channel Assign Comd

Conversation Starts


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Slide 16

Mobile Originated CallsMobile Originated Calls

MS BSS MSC VLR

Service Request - TMSI, Call Setup

MAP/B Service Request - TMSI, Call Setup

MAP/B - Fwd new TMSI

(SDCCH) RIL3-MM Reallocate New TMSI

(SDCCH) RIL3-MM Reallocation complete

MAP/B - TMSI Ack

(SDCCH) UA

(SDCCH) Service Request - TMSI, Call Setup

(SDCCH) SABM

(RACH) RIL3 - RR Channel Request

(AGCH - CCCH) RIL3 - RR IMM Assignment

Press Send

Encryption


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Slide 17

Mobile Originated Calls (contd 1)Mobile Originated Calls (contd 1)

MS BSS MSC VLR

(TCH) Conversation Starts

(TCH - FACCH)

(TCH - FACCH)

RIL3-CC Connect

RIL3-CC Connect Ack

(SDCCH) RIL3-CC Assign Complete

(TCH - FACCH) RIL3-CC Alerting

MAP/B Call complete

(SDCCH) RIL3-CC Call Proceeding

(SDCCH)

(SDCCH) RIL3 - CC Setup (Call Info)

MAP/B - Send Call Setup Info

RIL3-CC Channel Assign Comd


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Slide 18

Mobile Originated Calls (contd 2)Mobile Originated Calls (contd 2)

MS BTS 1 BSC BTS 2 MS

UA Frame

RIL3-RR Handover Complete

Resume Communication on New Channel

RSM RF Channel Release

RSM RF Channel Release Ack

RIL3-RR Handover Command

RIL3-RR Handover Access

RIL3-RR Physical Information

SABM Frame

Call in Progress

RSM Channel Activation

RSM Channel Activation Ack


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Slide 19

Channel ReleaseChannel Release

MS BSS MSC PSTN

Release (REL)

BSSMAP Release Complete

Conversation

BSSMAP Disconnect

Release Confirmed (REL CONF)

(FACCH) DTAP - Release

(FACCH) RIL3-RR Disconnect


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Slide 20

There are 3 purposes for handover:There are 3 purposes for handover: The first purpose is to rescue a call. If the call is not transferred

immediately, it will be lost.

The second purpose may be to reduce the interference that a

call in one cell may cause to calls in another cell. The third purpose is to ease traffic congestion by moving some

calls from a highly congested cell to a cell that is not so

congested.

HandoverHandover


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Slide 21

There are 3 types of handover:There are 3 types of handover: First, there is a handover from one radio to another of the same

or different BTS but same BSC

Second, there is a handover between channels of different

BSCs under the control of the same MSC Third there is a handover between channels under the control of

different MSCs in the same PLMN

Handover (Contd 1)Handover (Contd 1)


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Slide 22

MSC (a) MSC (b) MSC (c)

BSC (1) BSC (2)

Cell 1

Cell 2

Cell 3

Cell 4

Cell 5

Cell 6

Cell 7

Cell 8BTS BTS

BTS BTS

BSC (3) BSC (4)

4

3

3 41 2

1a 1b 2a 2b3a

3b4a

4b

PSTN

Handover (Contd 2)Handover (Contd 2)


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Slide 23

Layer 3 messages are essential for the control ofLayer 3 messages are essential for the control ofresources and for mobility managementresources and for mobility management

Simple call sequences highlight component parts of GSMSimple call sequences highlight component parts of GSM

architecture usedarchitecture used

Different types of handovers are supportedDifferent types of handovers are supported

SummarySummary

fresh field mtc 001 section 4

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