Cisco Cisco ASR 5000
MOCN for 2G SGSN
▀ How It Works
▄ SGSN Administration Guide, StarOS Release 18
How It Works
Automatic PLMN Selection in Idle Mode
This section briefly describes the normal PLMN selection procedure performed by MS along with modifications for
network sharing.
network sharing.
Whenever MS is switched on or has just returned to network coverage after being out of coverage, it tries to select a
network to register itself and receive network services. Traditionally, each network broadcasts its own PLMN-Id on
common broadcast channels that are visible to all MSs in that area.
network to register itself and receive network services. Traditionally, each network broadcasts its own PLMN-Id on
common broadcast channels that are visible to all MSs in that area.
The MS starts by scanning for all the available radio networks in that area and creating an Available PLMN list. It then
refers to the Equivalent PLMN list and Forbidden PLMN list (stored on its SIM) to prioritize the Available PLMN list.
Once this prioritized PLMN list is available, the MS attempts registration with a PLMN based on priority.
refers to the Equivalent PLMN list and Forbidden PLMN list (stored on its SIM) to prioritize the Available PLMN list.
Once this prioritized PLMN list is available, the MS attempts registration with a PLMN based on priority.
With network sharing a single radio network is shared by more than one network operator. Information about the
availability of multiple operators must be propagated to the MS so that it can correctly select a home or equivalent
network from all available networks.
availability of multiple operators must be propagated to the MS so that it can correctly select a home or equivalent
network from all available networks.
To advertise availability of multiple core network operators on a single radio network, broadcast information has been
modified to contain a list of PLMN-Ids representing core network operators sharing the particular radio network. The
traditional PLMN-Id broadcast by a radio network before network sharing support was available is known as a
“common PLMN Id”.
modified to contain a list of PLMN-Ids representing core network operators sharing the particular radio network. The
traditional PLMN-Id broadcast by a radio network before network sharing support was available is known as a
“common PLMN Id”.
An MS that does not support network sharing (a non-supporting MS) sees only the “common PLMN Id”, while an MS
supporting network sharing (a supporting MS) is able to see the list of PLMN-Ids along with “common PLMN Id”.
supporting network sharing (a supporting MS) is able to see the list of PLMN-Ids along with “common PLMN Id”.
A supporting MS is responsible for selecting an appropriate core network, while the RNC and SGSN will help select an
appropriate core network for a non-supporting MS.
appropriate core network for a non-supporting MS.
MOCN Configuration with Non-supporting MS
In this scenario, only the radio network is shared by different network operators while each operator manages its own
SGSN and the rest of the core network. The MS does not support network sharing – it is unable to understand the
modified broadcast information and would always choose the PLMN based on the advertised “common PLMN-Id”.
SGSN and the rest of the core network. The MS does not support network sharing – it is unable to understand the
modified broadcast information and would always choose the PLMN based on the advertised “common PLMN-Id”.
The SGSN performs the following steps:
1. Extract the subscriber’s IMSI.
If it is available, use IMSI in a BSSGP UL-UNITDATA message.
For inter-SGSN RAU and a P-TMSI Attach Request, retrieve the IMSI from the old SGSN or the MS
by doing an Identity Procedure.
2. Based on the MCC-MNC from the IMSI, apply roaming control.
3. If the subscriber can be admitted in the SGSN, send a response message (Attach-Accept or RAU-Accept) with
3. If the subscriber can be admitted in the SGSN, send a response message (Attach-Accept or RAU-Accept) with
an Redirection-Completed IE via BSSGP UL-UNITDATA.
4. If the subscriber cannot be admitted in the SGSN, send a BSSGP DL-UNITDATA message to the BSC with a
redirection indication flag set containing the reject cause, the attach reject message, and the original attach
request message received from the UE. The IMSI is also included in the message.
request message received from the UE. The IMSI is also included in the message.