Cisco Cisco ASR 5000
Serving GPRS Support Node (SGSN) Overview
Features and Functionality ▀
SGSN Administration Guide, StarOS Release 18 ▄
This mechanism is applicable in the following cases:
The UE is EPC-capable
The UE’s subscription has a GPRS subscription only (and not an EPS subscription)
If the subscription has an EPS subscription for an APN, then it is assumed that the P-GW addresses are configured in
the DNS for that APN.
the DNS for that APN.
Operator Policy Selection of S4 or Gn Interface
The S4-SGSN supports Operator Policy selection of either the S4 or the Gn interface for PDP context operations. This
feature allows flexible operator control over interface selection for operational or administrative reasons.
feature allows flexible operator control over interface selection for operational or administrative reasons.
This functionality overrides any other criteria for selection of the P-GW or the GGSN for PDP contexts. This feature is
applicable only for EPC-capable UEs.
applicable only for EPC-capable UEs.
IDFT Support During Connected Mode Handovers
The S4-SGSN supports the setup of indirect data forwarding tunnels (IDFT) between the eNodeB and the RNC via the
SGW during connected mode handovers. This allows the S4-SGSN to support connected mode handovers between the
UTRAN and E-UTRAN networks across the S3 interface.
SGW during connected mode handovers. This allows the S4-SGSN to support connected mode handovers between the
UTRAN and E-UTRAN networks across the S3 interface.
Once enabled, IDFT is employed under the following conditions:
If the SGSN is the old node participating in the connected mode handover, then indirect data forwarding
tunnels is used if:
The target node to which the connected mode handover is initiated should be an eNodeB (i.e., the
SGSN performs the handover to the MME).
The
enb-direct-data-forward
CLI setting is not configured as the source RNC configuration (in
RNC Configuration Mode).
If the SGSN is the new node participating in the connected mode handover, then indirect data forwarding
tunnels is employed if:
The source node from which connected mode handover is initiated is an eNodeB (i.e., the MME is
performing a handover to the SGSN).
The
enb-direct-data-forward
setting is not configured in the source RNC configuration (in RNC
Configuration Mode).
The source MME indicated that it does not support direct forwarding via a Forward Relocation Request.
Important:
If the target SGSN did not relocate to a new SGW, IDFT does not apply. The target SGSN sets up an
indirect data forwarding tunnel with SGW only if the SGW is relocated. If the SGW is not relocated, then it is the
source MME that sets up the indirect data forwarding tunnel between source the eNodeB and target RNC through the
SGW.
source MME that sets up the indirect data forwarding tunnel between source the eNodeB and target RNC through the
SGW.
Disassociated DSR Support
The S4-SGSN supports the disassociation of the SGSN and EGTP applications for a Delete Session Request in a certain
scenario. In this scenario, the SGSN application instructs the EGTP facility to send the Delete Session Request to the
scenario. In this scenario, the SGSN application instructs the EGTP facility to send the Delete Session Request to the