The IMSI Manager (IMSIMgr) is the de-multiplexing process that selects the Session Manager (SessMgr) instance to host a new session. The IMSIMgr selects the SessMgr instance based on a demux algorithm logic to host a new session by handling new calls requests from the MME Manager (MMEMgr), EGTPC Mgr, and the (e)SGTPCMgr (handles new MME handoffs). The new call requests or signaling procedures include Attach, Inter-MME TAU, PS Handover, and SGs, all of which go through the IMSIMgr. The IMSIMgr process also maintains the mapping of the UE identifier (e.g., IMSI/GUTI) to the SessMgr instance.
With the addition of support for the expanded capacities of the VPC-DI and ASR5500 platforms, the MME's IMSIMgr had become a bottleneck. With Release 18.0, the IMSI Manager Scaling feature increases the number of IMSIMgrs that can be made available on the MME - scaling from 1 to a maximum of 4 in releases prior to 21.0 and a maximum of 8 from release 21.0 onwards. The number is configurable (see Configuration section below).
IMSIMgr Scaling is only available on the ASR 5500 and the VPC-DI platforms. The maximum number of IMSIMgrs supported on the SSI platform remains at "1".
- It is possible to initiate an audit request for a single, specific IMSIMgr instance.
- Increased tolerance for configurable MME per service session limits. This can be visualized when configuring commands such as bind in the MME Service configuration mode.
- Increased tolerance for Attach rate control as the MME Attach rate control will be independently enforced by each IMSI Mgr instance.
Relationships to Other Features
The MME's use of the following features has been changed when multiple IMSIMgrs are configured:
- Attach Rate Throttling
- MME per service session limits
- Monitor Subscriber 'next call'
- Congestion Control
- MME traps generated by IMSI Manager
For details about the changes, refer to the How It Works section.