Cisco Cisco ASR 5000
SGSN Serving Radio Network Subsystem Relocation
How it Works ▀
SGSN Administration Guide, StarOS Release 18 ▄
How it Works
SRNS Relocation on the SGSN (Gn/Gp)
On the Gn/Gp SGSN, the SRNS relocation feature is triggered by subscribers (MS/UE) moving from one RNS to
another. If the originating RNS and destination RNS are connected to the same SGSN but are in different routing areas,
the behavior triggers an intra-SGSN Routing Area Update (RAU). If the RNSs are connected to different SGSNs, the
relocation is followed by an inter-SGSN RAU.
another. If the originating RNS and destination RNS are connected to the same SGSN but are in different routing areas,
the behavior triggers an intra-SGSN Routing Area Update (RAU). If the RNSs are connected to different SGSNs, the
relocation is followed by an inter-SGSN RAU.
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 Gn for PDP contexts. Note that the Gn/Gp SGSN SRNS relocation selection logic
is applicable in the following instances:
the interface used for a subscriber is Gn for PDP contexts. Note that the Gn/Gp SGSN SRNS relocation selection logic
is applicable in the following instances:
An S4-SGSN is configured (both the S4 license and EGTP service are available), but a given subscriber uses the
Gn interface for PDP contexts.
Only the Gn/Gp interfaces are utilized on the SGSN. S4 support is not configured.
Table 34.
Interface Selection Logic for SRNS Relocation on the SGSN Gn/Gp
SI.No RNC
Release
Compliance
Compliance
Target
Type
Sent in
Rel. Req.
Type
Sent in
Rel. Req.
LAC
Configured
as MME
Group ID?
Configured
as MME
Group ID?
LAC MSB
Set?
Set?
Peer Type?
DNS Query Type?
Interface
IP
Provided
by DNS?
IP
Provided
by DNS?
Interface
Chosen?
Chosen?
1
R8+
eNodeB
Not
Applicable
Applicable
Irrelevant MME
When the Gn
interface is used, the
system maps the eNB
ID to the RNC ID as
follows: The MSB 12
bits of the 20 bit eNB
ID is mapped to RNC
ID. DSN A query
with RNC ID FQDN
is sent and Gn
address is selected.
interface is used, the
system maps the eNB
ID to the RNC ID as
follows: The MSB 12
bits of the 20 bit eNB
ID is mapped to RNC
ID. DSN A query
with RNC ID FQDN
is sent and Gn
address is selected.
Gn
Gn
2
R8+
RNC
Not
Applicable
Applicable
Irrelevant SGSN
DNS A Query with
RNC ID FQDN
RNC ID FQDN
Gn
Gn
3
Pre R8
RNC
Irrelevant
Irrelevant It is not
important to a
Gn SGSN if the
peer is an MME
or an SGSN. For
a Gn SGSN, a
peer MME is
treated just like
an SGSN
Gn SGSN if the
peer is an MME
or an SGSN. For
a Gn SGSN, a
peer MME is
treated just like
an SGSN
DNS A Query with
RNC ID FQDN
RNC ID FQDN
Gn
Gn