About Layer 3 signaling [Under GSM]
Layer 2 and below is concerned mainly with point-to-point connection with BTS. Layer 3 signaling forms core of GSM. Let us have a brief look at "which components of Layer 3 of MS concern to which network elements". Refer a diagram below:
The main intent of RR is to take care of specifics of radio access. Thus RR communication is mainly between MS and BSS. Most of RR data is used by BSC, part of it is used by BTS and part is given to MSC. CM and MM data are relevant to MSC/VLR and HLR. In fact, MSC will contain peer entities MM and CM. Note that signaling between MSC, VLR, and HLR happen in terms of transactions. These transactions work on TCAP of underlying SS7 network. GSM standards specify protocol called Mobile Application Part (MAP) which work on top of TCAP.
RR along with L2 and L1 is known as Access Stratum (AS). CM and MM together known as Non-Access Stratum (NAS).
We will continue with GSM interfaces and protocol layers in next article.
References: GSM book by Mouly and Pautet, GSM Networks book by Heine
© Copyright Samir Amberkar 2010
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