Cisco Cisco ASR 5000
Idle Mode Signalling Reduction on the S4-SGSN
▀ How ISR Works
▄ SGSN Administration Guide, StarOS Release 18
The following scenarios are supported for 3G ISR:
ISR activation by 3G SGSN on new 3G SGSN RAU from MME
ISR activation by 3G SGSN on old 3G SGSN RAU to MME
ISR activation by 3G SGSN on new 3G SGSN SRNS relocation from MME (Connected mode IRAT handover
from MME to SGSN)
ISR activation by 3G SGSN on old 3G SGSN SRNS relocation to MME (Connected mode IRAT handover from
SGSN to MME)
Iu release triggered Release Access Bearer Request to SGW
Downlink data notification from SGW:
Downlink data notification UE responds to SGSN
Downlink data notification no response from UE
Stop paging indication
UE initiated detach for ISR activated subscriber under UTRAN
UE initiated detach under EUTRAN/MME initiated detach or Detach notification from MME
SGSN initiated detach for ISR activated subscriber
HSS/HLR initiated detach for ISR activated subscriber
ISR deactivation due to delete bearer request with ISR deactivation cause
ISR deactivation due to last PDN connection deletion (SGSN/UE/PGW/HSS/HLR-initiated)
ISR deactivation due to SGW change
ISR-deactivation due to context transfer between same Node types (S4 SGSN to and from S4 SGSN)
Intra-RAU without SGW change for ISR-activated subscriber
Intra-SRNS without SGW change for ISR activated subscriber
Limitations
There are no known limitations to the 2G ISR feature.
For the 3G SGSN, if an ISR is already active between the SGSN and an MME and the system receives a relocation
required towards an eNodeB served by the same ISR associated with the MME, the S4-SGSN first tears down the
existing S3 tunnel and will initiate a forward relocation request on a new tunnel. If the procedure completes
successfully, ISR association would be continued on the new tunnel. However, if the relocation is cancelled then the
tunnel is lost and the ISR is deactivated.
required towards an eNodeB served by the same ISR associated with the MME, the S4-SGSN first tears down the
existing S3 tunnel and will initiate a forward relocation request on a new tunnel. If the procedure completes
successfully, ISR association would be continued on the new tunnel. However, if the relocation is cancelled then the
tunnel is lost and the ISR is deactivated.
Call Flows
This section provides various call flows that illustrate the primary procedures used for the ISR feature:
2G ISR Activation by the S4-SGSN
The following illustration shows the ISR activation procedure when initiated by the S4-SGSN for a 2G subscriber.