16145901 GSM Protocols

8/7/2019 16145901 GSM Protocols

1/29

GSM Protocols

8/7/2019 16145901 GSM Protocols

2/29

GSM Architecture

8/7/2019 16145901 GSM Protocols

3/29

Interfaces

8/7/2019 16145901 GSM Protocols

4/29

Purpose of layeringDivides the complexity of internetworking intodiscrete steps.

Protocol: Set of rules that end points in atelecommunication connection use when theycommunicate.

8/7/2019 16145901 GSM Protocols

5/29

OSI Model

8/7/2019 16145901 GSM Protocols

6/29

OSI Reference ModelLayer were independent each other.Physical layer: Modulation, What kind of

channel, Decide the interface.Data link layer: Convert packets intoframes,Error detection and correction.Network Layer: Every network node has to

analyse.Ms bts bsc msc (RR)Routing, freagmentation

Transport Layer: Segmentation end to endordering packets

8/7/2019 16145901 GSM Protocols

7/29

Session Layer: Global synchronization Purpose.To differentiate mobile terminating call,

mobile,orginating call,location update.Presentation layer: Compression and decompression

Application Layer:

Provide the interface

8/7/2019 16145901 GSM Protocols

8/29

8/7/2019 16145901 GSM Protocols

9/29

GSM Protocol Stack

8/7/2019 16145901 GSM Protocols

10/29

Physical layer

8/7/2019 16145901 GSM Protocols

11/29

LAPDmThree different formats of identical length (23bytes) are defined; their respective usesdepend on the type of information to betransferred.A-FormatB-Format

Bibs-Format

8/7/2019 16145901 GSM Protocols

12/29

ISDN Channels

8/7/2019 16145901 GSM Protocols

13/29

LAPDm

8/7/2019 16145901 GSM Protocols

14/29

maximum frame length of an LAPDm frame (=23 byte or 184 bit)

Information frame: 1st byte, bit 0 = 0Supervisory frames: 1st byte, bit 0 = 1, bit 1 =0Unnumbered frames: 1st byte, bit 0 = 1, bit 1

= 1

8/7/2019 16145901 GSM Protocols

15/29

A-Format

Fill frame when no payload is available on anactive connection

Sent on any DCCH in both directions.

8/7/2019 16145901 GSM Protocols

16/29

Control Field

8/7/2019 16145901 GSM Protocols

17/29

Send Sequence Number and ReceiveSequence Number

P lli Bit (P Bit) Fi l Bit (F bit) d P/F

8/7/2019 16145901 GSM Protocols

18/29

Polling Bit (P-Bit), Final Bit (F-bit), and P/F-Bit

Polling Bit frame types that can be used onlyas commands

Final Bitframe types that can be used only as

ResponsesP/F-Bit frame types that can be used bothcommand and Response

8/7/2019 16145901 GSM Protocols

19/29

B-FormatTo transport the actual signaling data

Every DCCH and every ACCH use this format.

The maximum length of the Layer 3information to be carried is restricted,depending on the channel type (FACCH,SACCH).

8/7/2019 16145901 GSM Protocols

20/29

B-format

8/7/2019 16145901 GSM Protocols

21/29

SAPIThe number of unacknowledged frames for theservice access point identifier (SAPI) = 0 istwo, and the number of unacknowledgedframes for SAPI = 62 and for SAPI = 63 is one.

8/7/2019 16145901 GSM Protocols

22/29

C/R

8/7/2019 16145901 GSM Protocols

23/29

Bbis-format

For transmission of BCCH, PCH, and AGCH.There is no header in the Bbis-format thatwould allow for addressing or frame

identification.Addressing is not necessary, since BCCH, PCH,andAGCH are CCCHs, in which addressing is notrequired. In contrast to the DCCH, the CCCH

transports only point-to-multipoint messages.The Bbis format is required for thedownlink only.

8/7/2019 16145901 GSM Protocols

24/29

LAPD

8/7/2019 16145901 GSM Protocols

25/29

Identifier

distinguish among the variousTRXs. One TEI is assigned to eachTRX.That provides the ability todistinguish between TRXs during

analysis of a trace file.

8/7/2019 16145901 GSM Protocols

26/29

Layer3(RR,MM,CM)

8/7/2019 16145901 GSM Protocols

27/29

MM

8/7/2019 16145901 GSM Protocols

28/29

CM

8/7/2019 16145901 GSM Protocols

29/29

CM