Cisco Cisco ASR 5000
SGSN Serving Radio Network Subsystem Relocation
▀ How it Works
▄ SGSN Administration Guide, StarOS Release 18
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.
SGW during connected mode handovers.
Once enabled, IDFT is employed under the following conditions:
If the SGSN is the old node:
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:
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 setup does not apply at the SGSN. The
target SGSN sets up an indirect data forwarding tunnel with the 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.
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.
The following diagram illustrates the interface selection logic for S4-SGSN connected mode handovers.