Fresh Field Mtc 001 Section 4
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Transcript of Fresh Field Mtc 001 Section 4
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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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2001 Freshfield Communications Limited.Company Confidential Slide 3
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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2001 Freshfield Communications Limited.Company Confidential Slide 4
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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2001 Freshfield Communications Limited.Company Confidential Slide 5
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
Layer 3 MessagesLayer 3 Messages
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2001 Freshfield Communications Limited.Company Confidential Slide 6
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
Layer 3 MessagesLayer 3 Messages
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2001 Freshfield Communications Limited.Company Confidential Slide 7
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
Layer 3 MessagesLayer 3 Messages
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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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2001 Freshfield Communications Limited.Company Confidential
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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2001 Freshfield Communications Limited.Company Confidential
Slide 10
Location Area UpdateLocation Area Update
MS BSS MSC VLR HLR
(RACH)
(AGCH - CCCH)
(SDCCH)
(SDCCH)
(SDCCH)
(SDCCH)
(SDCCH)
RIL3 - RR Channel Request
RIL3 - RR IMM Assignment - Move MS to SDCCH
SABM Establishes the signalling link
UA
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2001 Freshfield Communications Limited.Company Confidential
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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2001 Freshfield Communications Limited.Company Confidential
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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2001 Freshfield Communications Limited.Company Confidential
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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2001 Freshfield Communications Limited.Company Confidential
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
RIL3 - RR Channel Request
Paging Response
MAP/B - Process Access
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2001 Freshfield Communications Limited.Company Confidential
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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2001 Freshfield Communications Limited.Company Confidential
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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2001 Freshfield Communications Limited.Company Confidential
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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2001 Freshfield Communications Limited.Company Confidential
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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2001 Freshfield Communications Limited.Company Confidential
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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2001 Freshfield Communications Limited.Company Confidential
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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2001 Freshfield Communications Limited.Company Confidential
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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2001 Freshfield Communications Limited.Company Confidential
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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2001 Freshfield Communications Limited.Company Confidential
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