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GPRS (Network PDP Act) - 22

Network PDP Activation [Under GPRS]
» GPRS description - 23.060 «
» Layer 3 - 24.007 «
» AT commands - 27.007 «

GGSN get N PDUs from external PDN. This N PDU could be for existing (active) PDP context. If so, GGSN tunels packet to appropriate SGSN. If the no PDP context exists, GGSN may need to go for network initiated PDP context activation. This can only be done when there is static information for the PDP address. GGSN may get this information from HLR or may have it to itself (this is operation specific). After these checks about PDP check, SGSN will have IMSI of MS to which N PDU is to be sent. To do it, GGSN has to initiate network initiated PDP context activation procedure as shown in diagrams below.

MS SGSN HLR GGSN
GGSN gets N PDUs; PDP context does not exist for corresponding PDP address. GPRS does the checks to allow network initiated PDP context activation. If checks are not ok, GGSN aborts PDN procedure.
If checks are ok, it mean GGSM knows IMSI of MS for which N PDUs are addressed. First step of network initiated PDP context activation would be to know SGSN to which MS is currently located.
Send Routing Info for GPRS
SRI for GPRS Ack
[IMSI, SGSN address]

PDU Notification Request
PDP Notification Response
This indicate that SGSN is ready to start PDP context activation procedure.
Request PDP Context Activation
[NSAPI, PDP type, PDP Address, QoS, APN etc.]

MS now will perform normal PDP context activation procedure using earlier values provided by network.

MN SM GMM LLC GRR AIR
SGSN would like to send PDP activate request.
DL TBF
DL TBF procedure is performed to transfer the request to MS.
GRR-DATA-IND
[LLC UI frame]
RLC in ack mode and LLC in Unack mode.
LLC-UNITDATA-IND
[SM PDU = Request PDP Context Activation]
GMM-SM-UNITDATA-IND
[SM PDU = Request PDP Context Activation]
SMREG-PDP-ACT-IND
[NSAP, QoS, PDP type, PDP address, APN etc.]

Adaptation (MN) layer now need to store this PDP context information and request PDP activation.
SMREG-PDP-ACT-REQ
[NSAP, QoS, PDP type, PDP address, APN etc.]
GMMSM-UNITDATA-REQ
[SM PDU = Activate PDP Context Req]
LL-UNITDATA-REQ
[SM PDU = Activate PDP Context Req]
GRR-DATA-REQ
[LLC UI frame, SAPI=Signaling]

UL TBF
At this time, One-phase access procedure will be performed to send LLC PDU.

The rest of the procedure remain same as MS initiated PDP context activation detailed in related article;

References: GPRS in Practice by McGuiggan

Copyright © Samir Amberkar 2010§

Inside PS - UL N PDU transfer « GPRS Index » Inside PS - DL N PDU transfer