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GPRS (Inside PS - UL N PDU transfer) - 21

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

Now let us look at how N PDUs are transferred in user/transmission plane.

APP SN LLC GRR AIR
Application user entity gives N PDUs to stack to transfer over GPRS.
N PDUs
SNDCP does buffering, compression, segmentation (to N201 bytes) and then invokes LLC QoS SAPI for transfer. SNDCP can keep on sending the segments (in SN PDU) to LLC. For Ack mode (reliability class 1-3), LLC-DATA-REQ should have internal reference so that when later confirmation comes from LLC in LLC-DATA-CNF, SNDCP can map it to segment to which it is sent. SNDCP buffers N PDU till confirm is not received for all its segments. For Unack mode, N PDU is deleted after all its segments are sent to LLC.
LL-DATA-REQ
[SN PDU]
LLC Ack and RLC ack assumed (reliability class 1 or 2). LL-UNITDATA-REQ if LLC Unack (reliability class 3, 4, or 5).
GRR-DATA-REQ
[LLC I frame]
LLC UI frame for LLC Unack mode.
RLC ack assumed (reliability class 1, 2, or 3). GRR-UNITDATA-IND for RLC Unack (reliability class 4 or 5).
UL TBF
Two-phase access procedure will be performed for uplink TBF. Refer article on two-phase.

Network LLC layer sends Receive Ready (received=sent) or Ack (received=sent-1) or SAck (otherwise) frame to acknowledge the received frames. Network may send acknowledgement by itself or on request from MS. MS requests acknowledgement by setting A(cknowledgement) bit in LLC header.
DL TBF
This DL TBF procedure for LLC RR/ACK/SAck frame (LLC Ack mode).
GRR-DATA-IND
[LLC RR frame]
Once confirmation is received for all segments sent for a N PDU, SNDCP deletes the N PDU.
LL-DATA-CNF
This procedure continues till N PDUs are sent (and acknoweldged for Ack mode).

References: GPRS in Practice by McGuiggan

Copyright © Samir Amberkar 2010§

Inside PS - MS PDP Act « GPRS Index » Network PDP Act