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S4-SGSN Suspend-Resume Feature
How it Works ▀
SGSN Administration Guide, StarOS Release 18 ▄
How it Works
S4-SGSN Suspend-Resume Feature
When a UE wants to make or receive a voice call via a GERAN circuit switched domain, and if the UE/BSS doesn't
support DTM mode, then the BSS sends a Suspend Request to the SGSN to suspend any packet data transmission. This
suspend request can be received on the same SGSN where a subscriber is already attached, or it can be received on an
SGSN where the subscriber is not yet attached.
support DTM mode, then the BSS sends a Suspend Request to the SGSN to suspend any packet data transmission. This
suspend request can be received on the same SGSN where a subscriber is already attached, or it can be received on an
SGSN where the subscriber is not yet attached.
SGSN where subscriber is attached: The SGSN initiates an intra-SGSN suspend procedure and will have to suspend
the data transmission all the way up to the PGW by sending a Suspend Request to the SGW/PGW. When the UE
completes the CS call, it will resume the packet transmission. The BSS will send a Resume request in this case.
the data transmission all the way up to the PGW by sending a Suspend Request to the SGW/PGW. When the UE
completes the CS call, it will resume the packet transmission. The BSS will send a Resume request in this case.
SGSN where subscriber is not yet attached: The SGSN initiates an inter-SGSN suspend procedure by sending a
GTPv2 / GTPv1 Suspend Request to the peer SGSN/MME. The peer node will suspend the data transmission. When the
UE completes the CS call, it may directly send a Routing Area Update request to the 2G SGSN to handover the packet
switched contexts. i The 2G SGSN will do a Context Request / Context Response / Context Ack procedure with the peer
node and will send a Create Session Request (if SGW relocation occurs) or a Modify Bearer Request (if no SGW
relocation occurs) to the SGW. The Modify Bearer Request at the PGW will be treated as an implicit Resume.
GTPv2 / GTPv1 Suspend Request to the peer SGSN/MME. The peer node will suspend the data transmission. When the
UE completes the CS call, it may directly send a Routing Area Update request to the 2G SGSN to handover the packet
switched contexts. i The 2G SGSN will do a Context Request / Context Response / Context Ack procedure with the peer
node and will send a Create Session Request (if SGW relocation occurs) or a Modify Bearer Request (if no SGW
relocation occurs) to the SGW. The Modify Bearer Request at the PGW will be treated as an implicit Resume.
Limitations
The following are the known limitations for the S4-SGSN Suspend/Resume feature:
1. If a suspend request aborts an ongoing RAU triggered SGW relocation, the Create Session Request will be
aborted and the PDN will be cleaned up. This is to avoid complexities in the state machine. If the system
retained PDP, the system would have to recreate the tunnel towards the old SGW to PGW before sending the
Suspend Notification. This would delay the Suspend procedure.
retained PDP, the system would have to recreate the tunnel towards the old SGW to PGW before sending the
Suspend Notification. This would delay the Suspend procedure.
2. A Suspend Request from the default SGSN in a pool to the SGSN serving the NRI of the given PTMSI is not
possible via the S16 interface due to a standards limitation. R10 specifications don't have a hop counter and
UDP source port IEs in the Suspend Notification message and hence this limitation. This is corrected in R11
specifications. TheS4-SGSN will support this call flow only in later releases.
UDP source port IEs in the Suspend Notification message and hence this limitation. This is corrected in R11
specifications. TheS4-SGSN will support this call flow only in later releases.
3. HSS initiated modification will be queued, if the Suspend preempts an HSS initiated modification while pending
for an Update Bearer Request from the PGW. The queued procedure will be restarted in a subsequent
procedure (RAU / Resume). Queued information will not be transferred to another RAT type, if a subsequent
procedure changes the RAT type.
procedure (RAU / Resume). Queued information will not be transferred to another RAT type, if a subsequent
procedure changes the RAT type.
4. A Suspend Acknowledge with rejected cause will not be sent to the peer SGSN/MME when an inter-SGSN
Suspend procedure is preempted by procedures such as RAU, Context Request, and Detach Request at the old
SGSN. Suspend Acknolwedge is not sent because it is very complex on the PMM-side to distinguish between
two procedures as the PMM has the same state for both the inter-SGSN Suspend procedure and the inter-SGSN
RAU procedure.
SGSN. Suspend Acknolwedge is not sent because it is very complex on the PMM-side to distinguish between
two procedures as the PMM has the same state for both the inter-SGSN Suspend procedure and the inter-SGSN
RAU procedure.
Call Flows
This section includes various diagrams that illustrate the Suspend/Resume call flow procedures, and the interface
selection logic:
selection logic: