Cisco Cisco ASR 5000
SGSN Pooling
▀ How it Works
▄ SGSN Administration Guide, StarOS Release 18
Address resolution without NRI
Address resolution without NRI is used for Inter-SGSN RAU between non-pooled areas or between multiple pools. In
this case the SGSN context request is routes towards the default SGSN, which in turn relays the GTP message to the
right SGSN based on the NRI value in the P-TMSI.
this case the SGSN context request is routes towards the default SGSN, which in turn relays the GTP message to the
right SGSN based on the NRI value in the P-TMSI.
Refer to the configuration section for the procedure to “Configure an Operator Policy”.
Mobility Inside the Pool
The distribution of UEs in a pool is handled by the BSCs/RNCs.
1. The UE sends an Attach Request or a RA Update Request to a SGSN.
2. This request passes through the BSC/RNC.
3. The BSC/RNC uses the NRI to locate the SGSN.
4. Once the SGSN is located Gb/Iu connection is set up.
If the NRI from the UE is invalid or does not match any of the NRIs of the pool members, the request is directed to one
of the pool members by the BSC/RNC. International Mobile Subscriber Identity (IMSI) attaches are also distributed
among the SGSN pool members by the BSCs.
of the pool members by the BSC/RNC. International Mobile Subscriber Identity (IMSI) attaches are also distributed
among the SGSN pool members by the BSCs.
Once a P-TMSI containing the NRI of a pool member has been assigned to an UE, the UE stays attached to that pool
member as long as it remains in that pool service area. The frequency of inter-SGSN RA updates decreases, as the UE
can move over a greater geographical area for one SGSN.
member as long as it remains in that pool service area. The frequency of inter-SGSN RA updates decreases, as the UE
can move over a greater geographical area for one SGSN.
Figure 94. Mobility inside the pool
Consider the scenario depicted in the diagram above: