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LTE - Service Request

LTE - end-to-end Service Request [Under LTE]
» E-UTRA and E-UTRAN overall description - 36.300, Rel 8 «
» E-UTRAN access - 23.401, Rel 8 «
» E-NAS - 24.301, Rel 8 «
» S1AP - 36.413, Rel 8 «
» GTPv2-C - 29.274, Rel 8 «
» RRC - 36.331, Rel 8 «

When UE is in RRC_IDLE/ECM-IDLE state, radio bearers are not present. In this state, UE wireless stack may receive user data (from IP/application) to be sent to PDN, MME may like to do NAS signaling witb UE (say Detach), or SGW may receive user data from PGW/PDN to be sent to UE. In such cases, "service request procedures" are triggered. We will take a case of SGW requiring service request procedures for sending user data in DL.

In earlier article, RRC/S1 release, we noted that when DL user data comes for UE - for which user plane TEID is not present, it gets buffered at SGW. Tunnel ID from SGW is present, but the one from eNB need to be allocated. Radio bearers are not present, so both SRBs and DRBs are need to be established. Further UE location is known at tracking area level, so UE need to be Paged and "told to start talking to the network".

Paging would make UE to request RRC Connection (through UL synchronisation/Random access) over which EMM Service Request message can be sent to MME.

MME then triggers S1-AP Initial Context Setup procedure so that eNB can appropriately establish (SRB2 and) DRBs and also GTP tunnels towards SGW. Note that information about tunnel IDs from SGW side is sent to eNB through S1-AP Initial Context Setup Request message. eNB, passes information about its own tunnel IDs to MME through S1-AP Initial Context Setup Complete message.

MME, in turn pass on this information to SGW through GTP-C Modify Bearer Request message.

LTE-service-request-742787.png

Copyright © Samir Amberkar 2010-12§

LTE - end-to-end RRC/S1 release « LTE Index » LTE - end-to-end TAU