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GPRS (RLC/MAC - One-phase cont.) - 10

RLC/MAC One-phase access continued [Under GPRS >> RLC/MAC]
» MS-BSS Interface; RLC/MAC - 04.60 «
» GPRS radio channels - 5.02 «
» Conformance tests - 51.010-1, section 41 «
» GMM procedures - 24.008 «

Let us continue GMM attach example.

MS has sent GMM attach request. At this point, MS listen to all PCCCH channels for paging and downlink assignment messages. Intent is to wait for response for GMM request sent. If network do not respond with downlink assignment, GMM procedure times out. MS then continue to listen to PCCCH for paging. We will take example of GMM procedure being timed out.

MS BTS

On network side, RLC/MAC receives LLC PDU containing GMM Authentication and Ciphering request

PCCCH
Wait for PAGING or DL ASSIGNMENT

MS side GMM procedure times out (READY timer expired), GMM in non-attached state.

PCCCH
Listen to PPCH

PPCH
PACKET PAGING REQUEST
RLC/MAC need to inform GMM about it (may be via LLC).

TBF establishment procedure will be triggered once MS side GMM gives go ahead.

PCCCH
Wait for USF=FREE (7).

PRACH
PACKET CHANNEL REQUEST
The reason would be paging response. After sending this request, MS listens to PCCCH for uplink assignment.

PCCCH
PACKET UPLINK ASSIGNMENT
Network gives single block allocation, TFI.

PDTCH
Empty LLC PDU
Contain TLLI for contention resolution at network side. Empty PDU works like a cell update (note that attach is not done yet). MS now listens to PACCH for further communication

PACCH
PACKET UPLINK ACK
This indicate contention resolution at network side is ok.

PACCH
PACKET DOWNLINK ASSIGNMENT
This message contain new TFI, PDTCH information. Earlier TFI is released. As this is downlink assignment, MS wait on assigned PDTCH.

PDTCH
BLOCK 0 (FBI=1)
This contain GMM Authentication and Ciphering request.

PACCH
PACKET DOWNLINK ACK
MS used RRBP received in above block to send ack.

This complete the TBF. Network releases the TFI.



MS BTS

GMM procedure require MS to send Authentication and Ciphering response. To do it, TBF establishment procedure will be triggered.

PCCCH
Wait for USF=FREE (7)

PRACH
PACKET CHANNEL REQUEST

PCCCH
PACKET UPLINK ASSIGNMENT

PDTCH
BLOCK 0 [CV=0, TLLI, assigned TFI]

PACCH
PACKET UPLINK ACK

PACCH
PACKET CONTROL ACK

This complete the TBF


References: GPRS in Practice by McGuiggan

Copyright © Samir Amberkar 2010§ §

RLC/MAC - One-phase access « GPRS Index » RLC/MAC - Two-phase access