Saturday, January 19, 2013

Closed Subscriber Group in lte (CSG)

         LTE - Closed Subscriber Group (CSG)


Closed Subscriber Group identifies a group of subscribers who are permitted to access one or more CSG cells of the PLMN.


To make a CSG call UE should send CSG Id to which it belongs and its access type in Attach request.


MME then performs UE authentication with the HSS and then exchanges Update Location Request and Answer. In Update Location Answer HSS sends CSG Information(CSG Id, Subscription timer) in Subscription data.

MME then verifies the CSG Id with the CSG received in Attach request if it matches then UE proceed the CSG call and sends Create session request with CSG Information IE to SGW. Upon receiving of successful response from SGW, MME sends Attach Accept message with Member status as ‘member’. After expiry of the Subscription timer for which UE is subscribed to attach with CSG cell, MME initiate PDN connection deletion.


What if CSG Id receive in Attach Request is not same as received in Subscription Data from HSS?

MME still make a successful call but for the specific time(300 sec) and send Attach Accept message to UE with Member status as ‘non-member’.
After expiry of non-member timer MME initiates PDN Connection deletion.


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