Cisco Cisco ASR 5000
SGSN Serving Radio Network Subsystem Relocation
▀ How it Works
▄ SGSN Administration Guide, StarOS Release 18
Step
Description
1
The source SRNC decides to perform/initiate SRNS relocation.
2
The source SRNC sends a Relocation Required message (Relocation Type, Cause, Source ID, Target ID, Source RNC to
target RNC transparent container) to the old SGSN.
target RNC transparent container) to the old SGSN.
3
The old SGSN determines from the Target ID that an inter-SGSN SRNS relocation is required. A DNS A query is
performed for the target RNC ID FQDN to obtain the target SGSN IP address. The old SGSN then sends a Forward
Relocation Request to the new SGSN.
performed for the target RNC ID FQDN to obtain the target SGSN IP address. The old SGSN then sends a Forward
Relocation Request to the new SGSN.
4
The new SGSN sends a Relocation Request message to the new RNC. At this point, radio access bearers have been
established.
established.
5
The new RNC sends a Relocation Request Response message to the new SGSN.
6
When resources for the transmission of user data between the new RNC and the new SGSN have been allocated and the
new SGSN is ready for relocation of SRNS, the Forward Relocation Response message (Cause, RANAP Cause, and RAB
Setup Information) is sent from the new SGSN to the old SGSN.
new SGSN is ready for relocation of SRNS, the Forward Relocation Response message (Cause, RANAP Cause, and RAB
Setup Information) is sent from the new SGSN to the old SGSN.
7
The old SGSN continues the relocation of SRNS by sending a Relocation Command message to the old RNC. The old
SGSN sends the RAB setup information received in the Forward Relocation Response in a Relocation Command to the old
RNC. This enables the old RNC to establish a data path with new RNC so that it can forward the data packets.
SGSN sends the RAB setup information received in the Forward Relocation Response in a Relocation Command to the old
RNC. This enables the old RNC to establish a data path with new RNC so that it can forward the data packets.
8
The old SRNC may, according to the QoS profile, begin the forwarding of data for the RABs to be subject for data
forwarding.
forwarding.
9
Before sending the Relocation Commit the uplink and downlink data transfer in the source, the SRNC shall be suspended
for RABs, which require a delivery order. The source RNC starts the data-forwarding timer. When the old SRNC is ready,
the old SRNC triggers the execution of relocation of SRNS by sending a Relocation Commit message (SRNS Contexts) to
the new RNC over the Iur interface.
for RABs, which require a delivery order. The source RNC starts the data-forwarding timer. When the old SRNC is ready,
the old SRNC triggers the execution of relocation of SRNS by sending a Relocation Commit message (SRNS Contexts) to
the new RNC over the Iur interface.
10
The target RNC sends a Relocation Detect message to the new SGSN when the relocation execution trigger is received.
11
The new RNC sends a RAN Mobility Information message. This message contains UE information elements and CN
information elements.
information elements.
12
When the new SRNC receives the RAN Mobility Information Confirm message, i.e. the new SRNC—ID + S-RNTI are
successfully exchanged with the MS by the radio protocols, the target SRNC initiates the Relocation Complete procedure
by sending the Relocation Complete message to the new SGSN.
successfully exchanged with the MS by the radio protocols, the target SRNC initiates the Relocation Complete procedure
by sending the Relocation Complete message to the new SGSN.
13
The old SGSN sends a Forward Relocation Complete message.
14
The old SGSN sends a Forward Relocation Acknowledgement to the new SGSN. to signal to the new SGSN the
completion of the SRNS relocation procedure.
completion of the SRNS relocation procedure.
15
Upon receipt of the Relocation Complete message, the CN switches the user plane from the old RNC to the new SRNC.
The new SGSN sends Update PDP Context Request messages to the GGSN.
The new SGSN sends Update PDP Context Request messages to the GGSN.
16
The GGSN sends Update PDP Context Response messages to the new SGSN.
17
The old SGSN sends an Iu Release Command message to the old RNC.
18
The old RNC sends an Iu Release Complete message to the old SGSN.
19
After the MS has finished the RNTI reallocation procedure, and if the new Routing Area Identification is different from the
old one, the MS initiates the Routing Area Update procedure.
old one, the MS initiates the Routing Area Update procedure.
The intra-SGSN Gn/Gp SRNS Relocation procedure is illustrated in the following figure.