The LINKMGR, GBMGR
and the MMEMGR select an IMSIMGR instance that needs to be contacted for
session setup. Each subscriber session in the Session Manager maintains the
IMSIMGR instance number that "hosts" the mapping for this IMSI. This
information is required while communicating during audit and session recovery
When a single IMSI
manager instance is present, there is only one centralized entry point for new
calls into the system. Network overload protection is configured using the
command "network-overload-protection", new call acceptance rates are configured
and controlled using this command. Once the configured rate is reached the new
calls are dropped. When there are multiple IMSI manager instances, the
configured new call acceptance rate is distributed equally across all IMSI
Manager instances to throttle new calls.
The IMSI manager
manages target (NRI and count) based offloading. Though number of IMSI Manager
instances is increased, only the first IMSI Manager instance is allowed to
perform the target based offloading. It keeps track of the total offloaded
subscribers for every Target-NRI from all Session Managers and notifies all the
Session Managers on attaining Target-count for that Target-NRI.
handling scenarios like ISRAU-Attach collision scenario, Inter-MME TAU attach
(FGUTI) on attach (IMSI) collision scenario and so on can occur, specific
measures have been taken to ensure these race handling scenarios are handled
correctly in a multiple IMSI Manager instance scenario.
The control plane
messaging throughput on the ASR 5500 platform is increased, therefore
Performance degradation or congestion is not observed during multiple IMSI
Manager instance recovery after a crash or an unplanned card migration. Also
mechanisms are devised to ensure there is no impact on Session Manager recovery
and Session Manager Thresholding.
subscriber next-call option is used to trace the next incoming call into the
system. With multiple IMSI Manager instances, the Session Controller now sends
the next-call details to IMSI manager instance 1. So the next incoming call
through IMSI manager instance "1" is monitored.
The IMSI managers
are updated with information on critical parameters that lead to congestion
control. The IMSI managers have to inform the congestion status to all Link
Managers and Gb Managers. In order to avoid multiple IMSI managers sending
information to all Link Managers and Gb Managers, only the first IMSI Manager
instance informs the congestion status to all Link Managers and Gb Managers.
Also only the first IMSI Manager instance sends the traps indicating congestion
status this reduces the number of traps to be sent.
From this release
onwards, the Diameter Proxy Server queries the IMSI Manager instances to obtain
IMSI/IMEI/MSISDN to Session manager instance mapping information.