GSM Signaling Protocol Architecture

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

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.

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

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.

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.

GSM Signaling Protocol Architecture

BSSAPThe 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.

GSM Signaling Protocol Architecture

BSSAPThe 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.

GSM Signaling Protocol Architecture

BSSAPThe 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

GSM Signaling Protocol Architecture

BSSAPThe 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

GSM Signaling Protocol Architecture

BSSAPThe 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.

GSM Signaling Protocol Architecture

BSSAPThe BSSAP user function is further subdivided into two separate functions:

•(DTAP)

•(BSSMAP)

BSSAP messages include the following fields:•DiscriminationDistribution between the two sub-protocols: BSSMAP and DTAP. •DLCIOnly 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.

GSM Signaling Protocol Architecture

BSSAPThe 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.

GSM Signaling Protocol Architecture

BSSAPThe BSSAP user function is further subdivided into two separate functions:

•(DTAP)

•(BSSMAP)

Message TypeA one octet field defining the message type. This mandatory field uniquely defines the function and format of each BSSMAP message.Information ElementEach 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.