Cisco Cisco ASR 5000
Serving GPRS Support Node (SGSN) Overview
Features and Functionality ▀
SGSN Administration Guide, StarOS Release 18 ▄
P-GW Initiated PDP Bearer Deactivation
The S4-SGSN supports the P-GW initiated PDP deactivation procedure in addition to the legacy MS initiated
deactivation procedure.
deactivation procedure.
The S4-SGSN processes Delete Bearer Requests received from the S-GW (sent by the P-GW) and deactivates the
requested bearers (PDP contexts) by sending a Deactivate PDP Context Request to the UE and then deactivates the PDP
context. If the S4-SGSN receives a Delete Bearer Request from the S-GW and the subscriber is in the PMM-IDLE /
GPRS-STANDBY state, it pages the UE before deactivating the PDP context request.
requested bearers (PDP contexts) by sending a Deactivate PDP Context Request to the UE and then deactivates the PDP
context. If the S4-SGSN receives a Delete Bearer Request from the S-GW and the subscriber is in the PMM-IDLE /
GPRS-STANDBY state, it pages the UE before deactivating the PDP context request.
In the case of 3G, the S4-SGSN will initiate RAB release procedures for the deactivated bearers. For 2G there is no
RAB release procedure.
RAB release procedure.
S-GW and P-GW Tunnel and EPS Subscription Recovery
The S4-SGSN supports session recovery procedures and recovers the S4 tunnel created for each subscriber assigned
PDP contexts through S4 interface. This functionality is part of session recovery procedures and allows sessions to be
reconstructed when the system recovers from a card-level software fault.
PDP contexts through S4 interface. This functionality is part of session recovery procedures and allows sessions to be
reconstructed when the system recovers from a card-level software fault.
The SGSN side TEID and the S-GW side TEID for the S4 tunnel are check-pointed and recovered during session
recovery. The S4-SGSN also recovers every PDN connection and their corresponding P-GW-side TEID.
recovery. The S4-SGSN also recovers every PDN connection and their corresponding P-GW-side TEID.
The S4-SGSN session recovery procedures have been enhanced to support recovery of EPS subscription data received
from the HLR / HSS. The EPS subscription information may contain a maximum of 50 APN profiles and each APN
profile contains an APN name string and a PDN GW FQDN string, which is check-pointed and recovered as part of the
enhanced session recovery procedures.
from the HLR / HSS. The EPS subscription information may contain a maximum of 50 APN profiles and each APN
profile contains an APN name string and a PDN GW FQDN string, which is check-pointed and recovered as part of the
enhanced session recovery procedures.
Local Configuration of S-GW and S4-SGSN per RAI
The SGSN already supports selection of the S-GW using DNS SNAPTR queries for the RAI FQDN. The S4-SGSN now
provides the option to configure a local S-GW address for a RAI (LAC, RAC MCC and MNC). This functionality
enhances the S-GW selection logic to allow the call to continue even if DNS lookup fails for any reason.
provides the option to configure a local S-GW address for a RAI (LAC, RAC MCC and MNC). This functionality
enhances the S-GW selection logic to allow the call to continue even if DNS lookup fails for any reason.
The S4-SGSN will select this local S-GW address based on the configured local policy. The local policy also can be
configured to allow the selection of the locally configured S-GW address when the DNS lookup fails.
configured to allow the selection of the locally configured S-GW address when the DNS lookup fails.
Local selection of the S-GW address applies in the following scenarios:
First PDP context activation for a subscriber
Intra SGSN routing area update
New SGSN routing area update
Intra SGSN inter RAT handover
Configurable GUTI to RAI Conversion Mapping
The S4-SGSN allows operators to configure mapping to an EPC MME for networks that already use LAC ranges
between 32768 and 65535.
between 32768 and 65535.
LAC ranges between 32768 to 65535 are currently being used in some UMTS/GPRS deployments although 3GPP TS
23.003 indicates that a UMTS / GPRS network should not use LACs in that range. This range is reserved for the MME
group code.
23.003 indicates that a UMTS / GPRS network should not use LACs in that range. This range is reserved for the MME
group code.