GSM interfaces in Core network - MAP [Under GSM]
GSM uses SS7 backbone for both signaling and transmission. ISUP is used for call channel setup and tear down. Addition for GSM is MAP (Mobile Application Part) - on top of TCAP - for rest of GSM signaling on network side. For example, when MS location is updated, (new) VLR - to which MS is located now - sends a TCAP transaction with (MAP) operation code updateLocation to HLR.
MAP acts as an wrapper for TCAP, making interface to application (MSC, VLR, HLR) GSM specific; in a way it standardises TCAP usage for GSM. Operation codes in component portion of TCAP indicated GSM signaling message/operation (like updateLocation) and the related parameters goes as (MAP) parameters in same component portion.
Below is stack for MSC, VLR, and HLR.
MAP uses Dialog portion (it is optional as per TCAP standard). Important parameter in Dialog portion is Application Context Name which contain Map version.
MAP provide general primitives (MAP-OPEN-REQ/IND, MAP-CLOSE-REQ/IND, MAP-DELIMITER-REQ/IND) for managing MAP transactions and special primitives (MAP-XXXX-REQ/IND) for acual GSM signaling like (MAP-updateLocation-REQ).
One of the reasons behind success of GSM is its MAP signaling, which is very well designed and uses already existing SS7 layers. In next chapter we will see examples of GSM signaling.
» 29.002 (MAP specification), 29.010 (Information Mapping between MS-BSS and BSS-MSC) «
We will continue with Core network interfaces in next article.
References: GSM book by Mouly and Pautet, GSM Networks book by Heine.
© Copyright Samir Amberkar 2010
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