GSM Signaling Protocol

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GSM Signaling Protocol

Architecture


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GSM Signaling Protocol Architecture

Protocols abovethe link layer of

the GSM signaling

protocol

architectureprovide specific

functions:

Radio Resource Management

Mobility Management

Connection Management

Mobile application part (MAP)

BTSManagement


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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.


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Control channels used by idle mode

mobiles to exchange signalinginformation, 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. (Followingthe request ofRACH
http://www.pulsewan.com/data101/gsm_basics.htmhttp://www.pulsewan.com/data101/gsm_basics.htm


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Mobility Management (MM-Layer)

Manages problem that arise frommobility 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.


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Connection Management

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 subscribers MSRN, subscribers HLR

have to query subscribers current VLR.


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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.


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BSSAP




(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 ofGSM Technical Specifications.


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BSSAP




(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


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BSSAP




(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


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BSSAP




(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.


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BSSAP




(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.

LengthSubsequent Layer3 message parameter length.


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BSSAP




(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.


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BSSAPThe BSSAP user function



(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.

GSM Signaling Protocol

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