Gsm signalling protocol

Signalling protocal in GSM.

1. GSM Signaling Protocol
Architecture

2. GSM Signaling Protocol Architecture
• Protocols above
the link layer of
the GSM signaling
protocol
architecture
provide specific
functions:
• Radio Resource Management
• Mobility Management
• Connection Management
• Mobile application part (MAP)
• BTS Management

3. GSM Signaling Protocol Architecture
Radio Resource Management (RR-
Layer)
The RR-Layer is concerned with the
management of RR-session, which is
the time that a mobile is in dedicated
mode, as well as the configuration of
radio channels. In addition RR-Layer
manages power control, discontinues
transmission and reception, and
handovers.

There are four types of handovers
1.Switching channels in the same cell.
2.Switching cells under control of the same Base Station Controller (BSC)
3.Switching cells under the control of different BSCs, but belonging to the
same Mobil service Switching Center (MSC)
4.Switching cells under control of different MSCs.

4. GSM Signaling Protocol Architecture
Control channels used by idle mode
mobiles to exchange signaling
information, required changing to
dedicated mode.
Mobiles in dedicated mode monitor the
surrounding Base Stations for handover
and other information.
The Control channels include:
Broadcast Control Channel (BCCH)
serves for BS identification, broadcasts,
and frequency allocations.

Frequency Correction Channel (FCCH) and Synchronization Channel (SCH)
– used for synchronization, and physical layer definition (time slots, burst
time…)
Random Access Channel (RACH) used by mobile to request access to the
network.
Paging Channel (PCH) used for locating the mobile user
Access Grant Channel (AGCH) used to obtain a dedicated channel. (Following
the request of RACH

5. GSM Signaling Protocol Architecture
Mobility Management (MM-Layer)
Manages problem that arise from
mobility of the subscriber.
In GSM,a group of neighbor cells is
grouped in one location area and
subscriber updates its position when
moving from one location area to
another. Paging is done only in the
current location area. This saves
bandwidth and un-necessary paging

The only question is "what division of cells to location areas is optimal?".
There are various algorithm for solving this problem, they are mostly based
statistical data.

6. GSM Signaling Protocol Architecture
Connection Management <CM-Layer>
This layer is based on application layer
with respect to the other layers.
E.g. An incoming mobile termination call
is directed to Gateway MSC (GMSC).
GMSC is basically a switch, which is
able to interrogate the subscribers HLR
to obtain routing information.
The routing information that is returned to GMS is the Mobile Station Roaming
Number (MSRN). MSRN are related to the geographical numbering plan, and
not assigned to subscribers. To obtain subscriber’s MSRN, subscriber’s HLR
have to query subscriber’s current VLR.

7. GSM Signaling Protocol Architecture
BSSAP
The BSSAP user function
is further subdivided into
two separate functions:
•(DTAP)
•(BSSMAP)
In the case of point-to-point calls the BSSAP uses one signalling connection per
active mobile station having one or more active transactions for the transfer of
layer 3 messages. In the case of a voice group or broadcast call there is always
one connection per cell involved in the call and one additional connection per BSS
for the transmission of layer 3 messages.

8. GSM Signaling Protocol Architecture
BSSAP
The BSSAP user function
is further subdivided into
two separate functions:
•(DTAP)
•(BSSMAP)
The Direct Transfer Application sub-Part (DTAP), also called GSM L3, is used to
transfer messages between the MSC and the MS (Mobile Station); the layer-3
information in these messages is not interpreted by the BSS. The descriptions of
the layer 3 protocols for the MS-MSC information exchange are contained in the
series of GSM Technical Specifications.

9. GSM Signaling Protocol Architecture
BSSAP
The BSSAP user function
is further subdivided into
two separate functions:
•(DTAP)
•(BSSMAP)
The BSS Management Application sub-Part (BSSMAP) supports other procedures
between the MSC and the BSS related to the MS (resource management,
handover control), or to a cell within the BSS, or to the whole BSS. The description
of the layer 3 protocol for the BSSMAP information exchange is contained in
Recommendation GSM

10. GSM Signaling Protocol Architecture
BSSAP
The BSSAP user function
is further subdivided into
two separate functions:
•(DTAP)
•(BSSMAP)
The BSS Management Application sub-Part (BSSMAP) supports other procedures
between the MSC and the BSS related to the MS (resource management,
handover control), or to a cell within the BSS, or to the whole BSS. The description
of the layer 3 protocol for the BSSMAP information exchange is contained in
Recommendation GSM

11. GSM Signaling Protocol Architecture
BSSAP
The BSSAP user function
is further subdivided into
two separate functions:
•(DTAP)
•(BSSMAP)
A distribution function located in BSSAP, which is reflected in the protocol
specification by the layer 3 header, performs the discrimination between the data
related to those two subparts.

12. GSM Signaling Protocol Architecture
BSSAP
The BSSAP user function
is further subdivided into
two separate functions:
•(DTAP)
•(BSSMAP)
BSSAP messages include the following fields:
•Discrimination
Distribution between the two sub-protocols: BSSMAP and DTAP.
•DLCI
Only for DTAP. Used in MSC to BSS messages to indicate the type of origination data link
connection over the radio interface.
•Length
Subsequent Layer3 message parameter length.

13. GSM Signaling Protocol Architecture
BSSAP
The BSSAP user function
is further subdivided into
two separate functions:
•(DTAP)
•(BSSMAP)
The BSS Management Application Part (BSSMAP) supports all of the procedures
between the MSC and the BSS that require interpretation and processing of
information related to single calls, and resource management. Some of the
BSSMAP procedures result in, or are triggered by, Radio Resource (RR)
management messages.

14. GSM Signaling Protocol Architecture
BSSAP
The BSSAP user function
is further subdivided into
two separate functions:
•(DTAP)
•(BSSMAP)
Message Type
A one octet field defining the message type. This mandatory field uniquely
defines the function and format of each BSSMAP message.
Information Element
Each IE has an identifier which is coded as a single octet. The length of an IE
may be fixed or variable and may or may not include a length indicator.