A P-GW initiates a
Secondary PDP activation by sending a Create Bearer Request (linked Bearer
Identity, Bearer Ctx(s), PCO etc) to the S-GW. The S-GW then forwards the
request to the S4-SGSN.
The Bearer Contexts
contain Bearer level parameters such as TFT, Bearer level QoS, S5/8-U PGW
FTeid, PCO, etc. The S-GW includes the S12-U SGW FTeid or S4-U SGW FTeid
depending on whether an S12 or S4 interface is used. The S4-SGSN sends the
Requested Secondary PDP Context Activation (linked Ti, Ti, Qos Requested, TFT,
and PCO) message to MS.
The QoS Requested,
TFT and PCO are transparently passed through the S4-SGSN. The MS sends an
Activate Secondary PDP Context Request (linked Ti, Ti, NSAPI, PCO, and QoS
Requested). Linked Ti, Ti, Qos Requested will be as same as received in a
previous message from the S4-SGSN. The TFT sent to MS may contain both the
uplink and downlink packet filters.
On receiving a
successful response (Activate Secondary PDP Context Request) in UMTS access,
the S4-SGSN establishes RAB with the serving RNC and then sends a Create Bearer
Response with Accepted cause to S-GW. For GPRS access, the RAB establishment is
The S4-SGSN includes
the S4-U SGW FTeid (received in Create Bearer Request) in the Create Bearer
Response to S-GW. S-GW uses this to correlate the Bearer Contexts in Response
with that of Request. The S4-SGSN completes the procedure by sending an
Activate Secondary PDP Context Accept to the MS.
A successful Network
Requested Secondary PDP Context Activation Procedure is illustrated in the
Figure 3. Call Flow:
Successful Network Requested Secondary Activation (S4-SGSN)