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GSM Protocols
GSM Architecture
Interfaces
Purpose of layering
Divides the complexity of internetworking into
discrete steps.
Protocol: Set of rules that end points in a
telecommunication connection use when they
communicate.
OSI Model
OSI Reference Model
Layer were independent each other.
Physical layer: Modulation, What kind of
channel, Decide the interface.
Data link layer: Convert packets into
frames,Error detection and correction.
Network Layer: Every network node has to
analyse.
Ms bts bsc msc (RR)
Routing, freagmentation
Transport Layer: Segmentation end to end
ordering packets
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
GSM Protocol Stack
Physical layer
LAPDm
Three different formats of identical length (23
bytes) are defined; their respective uses
depend on the type of information to be
transferred.
A-Format
B-Format
Bibs-Format
ISDN Channels
LAPDm
maximum frame length of an LAPDm frame (=
23 byte or 184 bit)
Information frame: 1st byte, bit 0 = 0
Supervisory frames: 1st byte, bit 0 = 1, bit 1 =
0
Unnumbered frames: 1st byte, bit 0 = 1, bit 1
=1
A-Format
Fill frame when no payload is available on an
active connection
Sent on any DCCH in both directions.
Control Field
Send Sequence Number and Receive
Sequence Number
Polling Bit (P-Bit), Final Bit (F-bit), and P/FBit
Polling Bit frame types that can be used only
as commands
Final Bit frame types that can be used only as
Responses
P/F-Bit frame types that can be used both
command and Response
B-Format
To transport the actual signaling data
Every DCCH and every ACCH use this format.
The maximum length of the Layer 3
information to be carried is restricted,
depending on the channel type (FACCH,
SACCH).
B-format
SAPI
The number of unacknowledged frames for the
service access point identifier (SAPI) = 0 is
two, and the number of unacknowledged
frames for SAPI = 62 and for SAPI = 63 is one.
C/R
Bbis-format
For transmission of BCCH, PCH, and AGCH.
There is no header in the Bbis-format that
would allow for addressing or frame
identification.
Addressing is not necessary, since BCCH, PCH,
and
AGCH are CCCHs, in which addressing is not
required. In contrast to the DCCH, the CCCH
transports only point-to-multipoint messages.
The Bbis format is required for the
downlink only.
LAPD
Terminal Endpoint
Identifier
distinguish among the various
TRXs. One TEI is assigned to each
TRX.
That provides the ability to
distinguish between TRXs during
analysis of a trace file.
Layer3(RR,MM,CM)
MM
CM
CM
.. .GSM Architecture Interfaces Purpose of layering Divides the complexity of internetworking into... Presentation layer: Compression and decompression Application Layer: Provide the interface GSM Protocol Stack Physical layer LAPDm Three different formats of identical length (23