layer3 signaling procedure

8/7/2019 Layer3 Signaling Procedure

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Layer 3 Signaling Procedures

By: Hamid Khurshid


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Signaling on Um interface


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Layer structure for Signaling on Um

interface Three layers implemented for signaling

between MS-BTS.

Entities belonging to same layer in differentnodes are called Peer Entities

Primitive carries information over thecommon boundary of adjacent layers at a

Service Access Point (SAP) Primitives also describe information exchange

between different layers and user application.


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Signaling Layer 3

Procedures included in layer 3 signalingprovide following main functions

Establish, maintain and terminate circuitswitched connections across GSM PLMN andother networks.

Supporting functions for supplementary

services and short message service control. Functions for mobility and radio resource

management.


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Sublayers of Signaling Layer 3

Three separate protocol control entities, in

three sublayers, are implemented in layer 3 to

realize these functions:

Connection Management (CM)

Mobility Management (MM)

Radio Resource Management (RR)


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Distribution of Sublayer entities in

network

Entities from all three sublayers are present in

MS.

MM and CM functions on network side arelocated in MSC.

On the network side RR functions mainly

reside in BSC but some of them may reside

and be interpreted by BTS and MSC.


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Connection Management Sublayer

(CM)

Call control and call related supplementary

services management (CC).

Short Message Service (SMS). Non call related supplementary services

management. (SS)


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Call Control Procedures (CC)

Provide functions and procedures for ISDN

call control, modified for adaptation to

radio environment.

Include call re-establishment and in-callmodification of bearer services.

Call specific supplementary services.

Parallel CC transactions are possiblethrough existence of more than one CC

entities.

CC signaling procedures are further


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Call Establishment Procedures

Procedures from upper layer are mapped on

CC procedures via exchange of primitives over

MNCCSAP (MS side) or in MSC (Network side).

Upper layers request establishment of

connection, null CC entity is selected.

Establishment is initiated by asking MM

sublayer to establish MM connection.

CC entity sends Setup message to its peer

entity.

Peers enter active state after exchan e of


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Active State Procedures

CC entity may inform its peer entity of a call

related event or call rearrangement by

Notify message.

Modify message maybe exchanged to

change the call mode in support of dual

services like alternate data/speech.


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Call Clearing Procedures

Disconnect message is sent to its peer by

the CC entity that initiates call clearing.

Release and ReleaseC

omplete messagesare exchanged afterwards.

MM connection is released by the MM

sublayer and CC entities return to null state.


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Miscellaneous Procedures

DTMF protocol control procedure is a

common example of this procedure class.

Status procedure is also an example of thisprocedure class which is initiated by any CC

entity that needs to know the call state of its

peer.


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Call Control Messages

Call establishment messages:

Alerting

Progress Call Confirmed

Call Proceeding

Connect

Connect Acknowledge

Emergency Setup

Setup


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Call information messages:

Modify

ModifyC

omplete Modify Reject

User Information

Call clearing messages:

Disconnect

Release

Release Complete


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Supplementary service control messages:

Facility

Hold Hold Acknowledge

Hold Reject

Retrieve

Retrieve Acknowledge

Retrieve Reject


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Miscellaneous messages:

Congestion Control

Notify Start DTMF

Start DTMF Acknowledge

Start DTMF Reject

Stop DTMF

Stop DTMF Acknowledge

Status

Status Enquiry


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Short Message Service Support

Procedures (SMS) Entities called Short Message Control (SMC)

provide services to SMS Application layer

through exchange of primitives via MNSMS-

SAP.

SMC entities use the peer protocol Short

Message Control Protocol (SM-CP) to transfer

short messages between MS and MSC.


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Short Message Service Support

Messages Short message service support messages are:

CP-Ack

CP-Data

CP-Error

RP-Ack

RP-Data

RP-Error


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Supplementary Services Support

(SS) Supplementary Services support procedures

handles services not related to a specific call.

SS messages are following: Facility

Register


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Mobility Management Sublayer

(MM) MM specific procedures

MM common procedures

MM connection management procedures


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MM Specific Procedures

These procedures realize the functions to

support the mobility of MS.

Provide the network with information of MSscurrent location.

Location updating type normal.

Location updating type periodic registration. Location updating type IMSI Attach and

Detach.


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MM Common Procedures

MM common procedures provide user

services for user identification and

confidentiality.

Authentication is handled by these

procedures.

TMSI reallocation.

Identification of MS by requesting IMSI or

IMEI.


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MM Connection Management

Procedures MM connection management procedures

provide services to entities in upper CM

sublayer.

Provide CM entities with ability to

communicate with peer entities using MM

connection.

When CM entity sends request for an MM

connection, MM sublayer sends request for RR

connection establishment to RR sublayer.

MM common procedures like Authentication


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Messages MM sublayer messages are divided into

four groups.

Registration messages are:

IMSI detach indication

Location updating request

Location updating accept

Location updating reject

Connection management messages:

CM service request

CM service accept


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Messages Security messages:

Authentication request

Authentication response

Authentication reject

Identity request

Identity response

TMSI reallocation command

TMSI reallocation complete



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Radio Resource Management

Procedures (RR)

To establish an RR connection, the RR entity

on MS side sends Channel Request message

and as a response dedicated channel is

allocated to the MS by Immediate

Assignment message.

Layer 2 frames SABM and UA are exchanged

and RR connection is established and MMsublayer in MS and network is informed that

RR connection exists.

RR connection can be released by normal


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Procedures (RR)

RR entity in MS sends the measurement

reports to the network in RR connection

established mode.

Upper layer entities send messages to their

peer entities using RR connection.

Handover procedure is also handled by RR

sublayer.

Classmark change procedure is also an

example of RR sublayer procedures.

Classmark interro ation rocedure can be


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Messages

Channel establishment messages:

Channel Request

Immediate Assignment

Immediate Assignment Extended

Immediate Assignment Reject

Assignment Command

Assignment Complete

Assignment Failure

Additional Assignment

Ciphering messages:


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Messages

Handover messages:

Handover Command

Handover Access

Handover Complete

Handover Failure

Physical Information

Channel release messages:

Channel release

Partial release


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Messages

System information messages:

System information type 1


System information type 2bis

System information type 2ter




System information type 5bis

System information type 5ter


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Messages


Channel mode modify

Channel mode modify acknowledge

Classmark change

Classmark enquiry

Frequency redefinition

Measurement report

Synchronization channel information

RR status


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Messages

Paging messages:

Paging request type 1



Paging response


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System Information Messages

System information messages contain the data

that MS needs to communicate with the

network.

System information messages are sent

continuously by the network (Downlink) on

BCCH (idle) and SACCH (dedicated) to all the

MS.

System information messages of type 1 to 4

are sent on BCCH and type 5 and 6 are sent on

SACCH.


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Specific system information messages are sent

in specific multiframe on BCCH.


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System information type 1:

Cell channel description

RACCH control parameters


Neighbor cells description

NCC permitted

RACH control parameters

System information type 2bis:

Neighbor cells description (extension)



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System information type 2ter:

Additional multiband information

Neighbor cells description (other bands)


Location area identification

Cell identity

Control channel description

Cell options

Cell selection parameters



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Cell selection parameters


CBCH channel description

CBCH mobile allocation

SI 4 rest octets


Neighbor cells description

System information type 5bis:


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System information type 5ter:

Additional multiband information

Neighbor cells description (other bands)



Cell identity

Cell options

NCC permitted


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L3 Message Format

Within the layer 3 protocols, with some

exceptions, the messages follow standard L3

format.

L3 message consists of octets, main parts of

which are:

Protocol discriminator

Transaction identifier or Skip indicator

Message type

Other information elements, as required


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Protocol Discriminator

Bits 1 to4 of first octet are protocol

discriminator (PD) bits.

Protocol discriminator identifies the layer 3

protocol to which the message belongs.


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Transaction Identifier and Skip

Indicator

Bits 5 to 8 of first octet in L3 message are

reserved for transaction identifier.

TI makes it possible to decide that to which

out of same parallel CM transactions the

message belongs.

For RR and MM messages the field is called

skip indicator and its value is fixed as 0000.

TI is further divided into two parts as bit 8 is

used to identify the direction of message and

remaining three bits make the value of TI.


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Message Type

The message type information element

determines the function of a message within a

protocol.

Each value represents a separate type of

message for the particular sublayer.


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Message Type


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MOC Signaling Diagram


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MTC Signaling Diagram


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Location Updating Signaling

Diagram


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layer3 signaling procedure

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