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GPRS (Inside PS - DL N PDU transfer) - 23

Inside PS - DL N PDU transfer [Under GPRS]
» GPRS description - 23.060 «
» Layer 3 - 24.007 «
» AT commands - 27.007 «

Let us look inside PS as how network delivers N PDU to MS

APP SN GMM LLC GRR AIR
Network would like to send N PDUs to MS. MS GPRS attached and PDP context is active. If GMM is in ready state, network can send packet dl assignment to start DL transfer. But if GMM is in standby state, network need to page the MS. We will take this scenario.
Paging
GMMRR-PAGE-IND
GMM restarts ready timer and "triggers" LLC. LLC need to send Cell update frame at this point to let network know the cell.
LLGMM-TRIGGER-REQ
GRR-DATA-REQ
[LLC Cell update frame]
UL TBF
One-phase access procedure is performed as shown in One phase cont. article.

MS need to now wait for downlink assignment. As per the assignment, MS downloads the RLC/MAC blocks.
DL TBF
GRR-DATA-IND
[LLC I frame]
LLC in ack mode
Once all segments are received, SNDCP sends assembled N PDU to Application user entity.
LL-DATA-IND
[SN PDU, TLLI]
N PDU

It depends on implementation as how SNDCP will interact with application.
LLC is in ack mode, so after receiving UI frame, it need to send Receive Ready frame.
GRR-DATA-REQ
[LLC RR frame]
LLC informs GMM about sending of data so that GMM can restart ready timer.
UL TBF
LLGMM-TRIGGER-IND
GMM restarts ready timer.

Above procedure is repeated as per the availability user data.

References: GPRS in Practice by McGuiggan

Copyright © Samir Amberkar 2010§

Network PDP Act « GPRS Index » Inside PS - Cell/RA update