GSM Protocol Stack

Shrish Mammattva Bajpai

What is Protocol Stack ?

A protocol stack (sometimes communications stack) is a particular software implementation of a computer networking protocol suite. The terms are often used interchangeably. Strictly speaking, the suite is the definition of the protocols, and the stack is the software implementation of them.

In Windows the TCP/IP stack is implemented by the Winsock DLL.

What is Protocol Stack ?

The term stack also refers to the actual software that processes the protocols. So, for example, programmers sometimes talk about loading a stack, which means to load the software required to use a specific set of protocols.

Um Interface

A Interface

MS End Protocol Stack

• Physical Layer• Data Link Layer• Layer 3 Radio Recourse Management Mobility Management Connection Management

BTS End Protocol Stack

• Physical Layer• Data Link Layer• Layer 3 Radio Recourse Base Transreceiving Station

Management

BSC End Protocol Stack

• Physical Layer• Data Link Layer• Layer 3 Radio Recourse Base Tranreceiving Station Management Signaling Connection Control Part Direct Transfer Application Part Base Station Subsystem Management

Application Part

MSC End Protocol Stack

Message Transfer Part Signaling Connection Control Part Direct Transfer Application Part Base Station Subsystem Management Application

Part Connection Management Mobility ManagementMobile Application PartTransaction Capabilities Application Part.

Link Layers

Um Interface

• Physical Layer Implement Logic channels,coding and frames.

Access Capabilities. Error Detection. Encryption.

Um Interface Physical Layer Mode

• Mode of operations Idle Mode. Dedicated Mode.

Um Interface Physical Layer Mode

Um Interface Physical Layer Frame

Um Interface Physical Layer Frame

• 21 Blocks.• Power level.• Timing advance. Use by ACCH, CCCH, BCCH & DCCH.

Um Interface Data Link Layer Task

Um Interface Data Link Layer Operation Mode 1

• Unacknowledged Operation Data Transmitted in UI frame. No Ack No Flow control Mechanism. No L2 error correction technique. Use for all channels except RACH. .

Um Interface Data Link Layer Operation Mode 2

• Acknowledged Operation Mode Data Transmitted in I frame.

+ Ve Ack Flow control Mechanism. Error correction technique. Use for DCCH Channel

Um Interface Data Link Layer

Um Interface Data Link Layer

Connection End Point Identifiers of L2 connections are labeled with Data Ling Layer Identifiers

1.Service Access End Point Identifiers 2.Connection End Point Identifiers SAPI =0 for Signaling. SAPI = 3 for SMS.

Um Interface Data Link LayerProcedure 1

• Distribution Procedure SAP is associated with only one signaling

channel Distribution of L2 frame receive by one

channel to the respective data link procedure. Not used for RACH

Um Interface Data Link LayerProcedure 2

• Random Access Procedure Only for RACH

Unidirectional Procedure Deals with random control procedure Retransmission of Random Access Brust

Um Interface Data Link LayerFrame Formats 1

Points No flag at start and at last.

Octets are depend upon type of channel. The end of information field is given by length

indicator. Frame format contains address field and

variable length. Connection of SAPI = 0 is initiated by MS. Address Field is one for control channels

Um Interface Data Link LayerFrame Formats 2

Um Interface Data Link LayerFrame Formats

• Type A. Used in dedicated channels

Bi-directional Use. No Information Contain. Ack Mode Operation.

Um Interface Data Link LayerFrame Formats 2

Um Interface Data Link LayerFrame Formats

• Type B.

Used in dedicated channels

Bi-directional Use. Information Contain. Ack Mode Operation.

Um Interface Data Link LayerFrame Formats

Um Interface Data Link LayerFrame Formats

• Type Bbis

Used in common control channels

Uni-directional Use. Information Contain. Un Ack Mode Operation. SAPI =0 is used.

Um Interface Data Link LayerFrame Formats

Um Interface Data Link LayerFrame Formats

• Type Abis

Used in common control channels

Uni-directional Use. No Information Contain. Un Ack Mode Operation. SAPI =0 is used.

Um Interface Layer 3

• Layer 3 RR Management. CM Management. MM Management.

Um Interface Layer 3 Frame Format 1

• Common for RR, MM and CM.

Um Interface Layer 3 Frame Format 2

• Transaction ID- Enable to perform several parallel signaling transaction.

• Protocol Discriminator – Operation type.

• Message Type – Different type of process.

• Information ID – Information elements.

• Length Indicator – Length of the Information ID.

Um Interface Layer 3 Radio Recourse Management. Functions

Um Interface Layer 3 Radio Recourse Management. Processes

• Connection Set Up And Release.• Handoff.• Channel Change• Ciphering.

Um Interface Layer 3 Radio Recourse Management. Connection

Set Up And Release Processes

Um Interface Layer 3 Radio Recourse Management. Connection

Set Up And Release Processes

Um Interface Layer 3 Radio Recourse Management. Connection

Set Up And Release Processes

Um Interface Layer 3 Radio Recourse Management. Connection

Set Up And Release Processes• RR Connection between MS & Nwk..• LAPDm Connection between MS &

Nwk..• Initiated by MS or Nwk. .• RR connection Establish then higher

link comes in picture.• SAPI =0 is used.

Um Interface Layer 3 Radio Recourse Management. Channel

Change Processes

Um Interface Layer 3 Radio Recourse Management. Channel

Change Processes• Requested By CM, MM or by RR.• Initiated By Nwk..• MS get assignment command to

shut down the connection.

Um Interface Layer 3 Radio Recourse Management. Handoff

Process

Um Interface Layer 3 Radio Recourse Management. Handoff

Process

Um Interface Layer 3 Radio Recourse Management. Handoff

Process• Cell Information BCCH• Handoff Command ACCH• Handoff Access DCCH

Um Interface Layer 3 Radio Recourse Management. Activation of

Ciphering Process

Um Interface Layer 3 Radio Recourse Management. Activation of

Ciphering Process• Done By BSS.• MS get the message and done the

task.

Um Interface Layer 3 Mobility Management Functions

Um Interface Layer 3 Mobility Management Process

• Common Mobility Management Process. TMSI Assignment. Identification Process. Authentication Process. IMSI Detach.

• Specific Mobility Management Process IMSI Attach

Location Updation.

MM Connection Management Process

Um Interface Layer 3 Mobility Management Process. TMSI

Assignment 1

Um Interface Layer 3 Mobility Management Process. TMSI

Assignment 2• Unique identifier for each MS• Change with every location

updation.• Send through BCCH with LAI

identifier.

Um Interface Layer 3 Mobility Management Process. Identification

Process. 1

Um Interface Layer 3 Mobility Management Process. Identification

Process. 2• At any time when network wants.• IMSI + IMEI sends to Network.

Um Interface Layer 3 Mobility Management Process.

Authentication Process. 1

Um Interface Layer 3 Mobility Management Process.

Authentication Process. 2• Started by Network, when MS send the

request to establish RR connection.• RAND and Kc.• When fails then IMSI and TMSI will send.• Two time only.• Fail then cancel all the connections.• Emergency Calls can made only.

Um Interface Layer 3 Mobility Management Process. IMSI Detach. 1

Um Interface Layer 3 Mobility Management Process. IMSI Detach. 2

• Switch off the cell.• Cancel the paging load from network.• Send the message to MS on BCCH and

SCCH.• This process will start after the any

specific operation.

Um Interface Layer 3 Mobility Management Process. Location

Upadation• Channel Used BCCH.• Identifier TMSI & LAI.• Register HLR & VLR.

Um Interface Layer 3 Mobility Management Process. IMSI Attach.

• Switch on the cell.• New TMSI and LAI.

Um Interface Layer 3 Connection Management

• Three Entities 1.Call Control. 2.Supplementary Services. 3. Short Message Services.

Um Interface Layer 3 Connection Management

A Interface Protocol Stack

Message Transfer Part Signaling Connection Control Part Direct Transfer Application Part Base Station Subsystem Management Application

Part Connection Management Mobility ManagementMobile Application PartTransaction Capabilities Application Part.

A Interface Message Transfer Part

• Comprise lower 3 layer of OSI model.• Routing.• Transportation of the signaling

message.

A Interface Mobile Application Part

A Interface Signaling Connection Control Part

• Provides Connection less and connection oriented Services.

• Messages through BSC.• Two Reasons for setting the SCCP

Connection. 1.Location Update. 2.Call Connection Setup.

A Interface Transaction Capabilities Application Part

• Connectionless Service given By SCCP.

• Exchange of MAP messages(Between different MSC, HLR, VLR and GMSC) done through this part.

A Interface Base Station System Application Part

• Two Parts Base Station System Management Application

Part. Direct Transfer Application Part.

A Interface Direct Transfer Application Part.

• The messages through CM & MM are passed on transparently through BSS using DTAP Protocol.

• Only Connection Oriented Services.• One signaling connection for each

active MS with one or more transaction.• New connection establish each time

when the new transaction start between MS and MSC.

A Interface BSSMAP

• Responsible for all admin and control of the radio recourses.

• Handoff and channel ass. is control by BSSMAP.

• Two type of procedure. 1.Global BSSMAP procedure. 2.Dedicated BSSMAP procedure.

A Interface BSSMAP Dedicated BSSMAP procedure

• Channel Assignment.• Channel Release.• Cyphering Control.

A Interface BSSMAP Dedicated BSSMAP procedure

A Interface BSSMAP Global BSSMAP procedure

• Paging• Flow Control• Closing and Opening of the

channel.

A Interface BSSMAP Global BSSMAP procedure

Abis Interface BTSM

• Task Random Access of the channel.

Paging process of MS. Ciphering process of MS. Power Control of MS.

Abis Interface BTSM Frame

Abis Interface BTSM Frame

• Message Discriminator 1 for passes through BTS. 2-5 serve by BTS.