Cisco Cisco ASR 5000
SGSN Serving Radio Network Subsystem Relocation
How it Works ▀
SGSN Administration Guide, StarOS Release 18 ▄
UTRAN-to-E-UTRAN connected mode Inter-RAT handover over the S3 interface
E-UTRAN-to-UTRAN connected mode Inter-RAT handover over the S3 interface
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
S4-SGSN SRNS relocation interface selection logic is based on the following assumptions:
If the egtp-service is configured, it is assumed the network is EPC capable and therefore must require a DNS
SNAPTR.
If the egtp-service is configured on the S4-SGSN, then for outbound SRNS relocation, the system always
performs a DNS SNAPTR as follows:
x-S16 if the peer detected is another S4-GSN, or x-S3 if the peer detected is an MME (based on
whether the target is an eNodeB/the MSB of the target LAC being 1, or, if a local MME group ID is
configured).
configured).
x-gn if a local configuration for a peer SGSN or MME exists with a Gn address, or, if DNS SNAPTR
returned a GN address.
If both DNS queries fail, the system rejects the SRNS relocation.
The following table describes the interface selection logic for the various types of SRNS relocation that can occur when
the interface used for a subscriber is S4 for PDP contexts.
the interface used for a subscriber is S4 for PDP contexts.
Table 37.
Interface Selection Logic for S4-SGSN SRNS Relocation
SI.No RNC
Release
Compliance
Compliance
Target Type Sent
in Relocation
Request
in Relocation
Request
LAC
Configured
as MME
Group ID?
Configured
as MME
Group ID?
LAC MSB
Set?
Set?
Peer
Type?
Type?
Type of DNS
Query?
Query?
Interface
IP
Provided
by DNS?
IP
Provided
by DNS?
Interface Chosen?
1
R8+
eNodeB
n/a
n/a
MME
DNS
SNAPTR
w/ service
type x-
3gpp-
mme:x-s3
and TAC
FQDN
SNAPTR
w/ service
type x-
3gpp-
mme:x-s3
and TAC
FQDN
S3
S3