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BSSMAP (Base Station Subsystem Management Application Part)

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Introduction:

The Base Station Subsystem Management Application Part (BSSMAP) is a protocol used in mobile communication systems to facilitate communication between the Mobile Services Switching Center (MSC) and the Base Station Subsystem (BSS). The protocol is used to manage calls, handovers, and other signaling functions within the GSM (Global System for Mobile Communications) network. In this article, we will explain in detail what BSSMAP is, its functions, and the different messages involved.

Overview:

The BSSMAP is a signaling protocol used in the control plane of the GSM network. It is part of the Signaling System No.7 (SS7) protocol suite and is used to control the functions of the BSS. The BSS is responsible for managing the radio resources used by mobile stations (MS) within its coverage area. It comprises one or more base transceiver stations (BTS) and a base station controller (BSC) that manages and controls the BTSs.

Functions of BSSMAP:

The BSSMAP protocol performs various functions in the GSM network. These include:

  1. Call establishment and release: The BSSMAP protocol is used to set up and release calls between the mobile station (MS) and the MSC. The protocol exchanges messages between the BSS and the MSC to initiate and terminate calls.
  2. Handover management: The BSSMAP protocol is also responsible for managing handovers between different cells within the BSS. When a mobile station moves from one cell to another, the BSSMAP protocol is used to initiate a handover and ensure a smooth transition without losing the call.
  3. Paging and location management: The BSSMAP protocol is responsible for managing the location of mobile stations within the BSS. When the MSC needs to locate a mobile station, it sends a paging message to the BSS, which then sends a paging message to all the BTSs in the area to locate the mobile station.
  4. Authentication and security: The BSSMAP protocol is responsible for authenticating and securing communications between the MS and the MSC. This is achieved through the exchange of authentication and encryption keys between the MS and the MSC.
  5. SMS management: The BSSMAP protocol is also used to manage Short Message Service (SMS) messages between the MS and the MSC. The protocol exchanges messages to set up and release SMS sessions and to deliver SMS messages.

BSSMAP Messages:

The BSSMAP protocol uses various messages to exchange information between the BSS and the MSC. These messages include:

  1. Assignment Request (ASSREQ): The ASSREQ message is sent by the BSS to the MSC to request a dedicated channel for a call.
  2. Assignment Complete (ASSCOMP): The ASSCOMP message is sent by the MSC to the BSS to confirm the assignment of a dedicated channel for a call.
  3. Handover Request (HO REQ): The HO REQ message is sent by the BSS to the MSC to request a handover of a call from one cell to another.
  4. Handover Request Acknowledge (HO REQ ACK): The HO REQ ACK message is sent by the MSC to the BSS to acknowledge the handover request and provide instructions for the handover.
  5. Paging Request (PAG REQ): The PAG REQ message is sent by the MSC to the BSS to request the location of a mobile station.
  6. Paging Response (PAG RES): The PAG RES message is sent by the BSS to the MSC to report the location of a mobile station.
  7. Authentication Request (AUTH REQ): The AUTH REQ message is sent by the MSC to the MS to request authentication information.
  8. Authentication Response (AUTH RES): The AUTH RES message is sent by the MS to the MSC to provide authentication information.
  9. Cipher Mode Command (CMC): The CMC message is sent by the MSC to the MS to set up encryption for communication.
  10. Cipher Mode Complete (CMPL): The CMPL message is sent by the MS to the MSC to confirm the encryption setup.
  11. SMS Submit (SMS-SUBMIT): The SMS-SUBMIT message is sent by the MS to the MSC to submit an SMS message.
  12. SMS Delivery (SMS-DELIVER): The SMS-DELIVER message is sent by the MSC to the MS to deliver an SMS message.

BSSMAP Protocol Stack:

The BSSMAP protocol is part of the SS7 protocol suite and is layered on top of the Message Transfer Part (MTP) layer. The MTP layer provides reliable message delivery between network elements, while the BSSMAP layer provides signaling functions specific to the BSS.

The BSSMAP protocol stack consists of three layers:

  1. BSSMAP User Part (BSSMAP): The BSSMAP layer provides the signaling functions specific to the BSS, such as call setup, handover management, and location management.
  2. SCCP (Signaling Connection Control Part): The SCCP layer provides additional functions for the SS7 protocol suite, such as routing and error handling.
  3. MTP (Message Transfer Part): The MTP layer provides reliable message delivery between network elements.

Conclusion:

The BSSMAP protocol is a crucial component of the GSM network, responsible for managing calls, handovers, and other signaling functions between the BSS and the MSC. It provides functions for call establishment and release, handover management, paging and location management, authentication and security, and SMS management. The protocol uses various messages to exchange information between the BSS and the MSC, and it is layered on top of the MTP and SCCP layers in the SS7 protocol suite. Understanding the BSSMAP protocol is essential for network engineers and administrators to ensure efficient and reliable operation of the GSM network.