Cisco Cisco ASR 5000
Serving GPRS Support Node (SGSN) Overview
▀ Features and Functionality
▄ SGSN Administration Guide, StarOS Release 18
SGW and not respond back to the SGSN application to confirm the action. In effect, the SGSN application disassociates
itself from the EGTP facility. Since the SGSN application is no longer waiting for a response from the EGTP facility,
there will be reduced internal communication between the SGSN and EGTP. The the EGTP facility will handle
retransmissions of the DSR request, thereby eliminating the possibility of hanging sessions at the SGSN.
itself from the EGTP facility. Since the SGSN application is no longer waiting for a response from the EGTP facility,
there will be reduced internal communication between the SGSN and EGTP. The the EGTP facility will handle
retransmissions of the DSR request, thereby eliminating the possibility of hanging sessions at the SGSN.
The behavior of the disassociated DSR feature for each of the applicable scenarios follows:
1. The SGSN / MME wants to send a DSR with OI=0 and SI=1 to an old SGW during SGW relocation.
2. The SGSN application instructs the EGTP facility to inform the old SGW of the DSR and the SGSN doesn't
2. The SGSN application instructs the EGTP facility to inform the old SGW of the DSR and the SGSN doesn't
expect any response from EGTP.
3. The EGTP facility handles retransmissions of this DSR request.
SGSN Serving Radio Network Subsystem (SRNS) Relocation Support
SRNS relocation is the method defined in 3GPP TS 23.401 for connected mode inter-RAT handovers from E-UTRAN
to UTRAN or UTRAN to E-UTRAN networks. The SGSN already supports SRNS relocation across the Gn interface.
The SGSN now also supports SRNS relocation with the following cases across the S3 (S4-SGSN to MME) and S16
(S4-SGSN to S4-SGSN) interfaces:
to UTRAN or UTRAN to E-UTRAN networks. The SGSN already supports SRNS relocation across the Gn interface.
The SGSN now also supports SRNS relocation with the following cases across the S3 (S4-SGSN to MME) and S16
(S4-SGSN to S4-SGSN) interfaces:
Intra-SGSN SRNS relocation
Inter-SGSN SRNS relocation over the S16 interface
UTRAN-to-E-UTRAN connected mode Inter-RAT handover over the S3 interface
UTRAN-to-E-UTRAN connected mode Inter-RAT handover over the S3 interface
The relocation feature is triggered by subscribers (MS/UE) moving between an eNodeB and an RNC. If the originating
and destination nodes are connected to the same S4-SGSN but are in different routing areas, the behavior triggers an
intra-SGSN Routing Area Update (RAU). If the nodes are connected to different S4-SGSNs, the relocation is followed
by an inter-SGSN RAU.
and destination nodes are connected to the same S4-SGSN but are in different routing areas, the behavior triggers an
intra-SGSN Routing Area Update (RAU). If the nodes are connected to different S4-SGSNs, the relocation is followed
by an inter-SGSN RAU.
As part of the SRNS relocation feature implementation on the S4-SGSN, the SGSN application also supports the gtpv2
(egtp) protocol for:
(egtp) protocol for:
Inter-SGSN SRNS relocations over the S16 interface
MME - SGSN SRNS relocations over the S3 interface
A command is available to enable the SGSN to support SRNS relocation when the source RNC is behaving as the target
RNC.
RNC.
Configuration and Maintenance
The existing
srns-inter
and
srns-intra
commands in Call Control Profile Configuration Mode are used to enable
this feature.
In addition, the
enb-direct-data forward
command in RNC Configuration Mode can be used to enable the S4-
SGSN to apply direct forwarding tunnels or indirect data forwarding tunnels (IDFT) between a particular eNodeB and
RNC.
RNC.
Statistics are also available with the show s4-sgsn statistics all command that enable operators to track SGW
relocations and SRNS procedure aborts.
relocations and SRNS procedure aborts.
E-UTRAN Service Handover Support
The SGSN supports configuration-based enabling of the E-UTRAN Service Handover Information Element, which is
optional in the following RANAP messages used during SRNS relocation:
optional in the following RANAP messages used during SRNS relocation: