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Cisco BTS 10200 Softswitch Troubleshooting Guide, Release 5.0.x
OL-8723-19
Appendix C Overload Control
Reducing Overload
Reducing Overload
When MCL exceeds MCL0, Overload Control reduces MCL as follows:
•
Selectively reject new calls by the signaling adapters—A percentage of calls and messages are
rejected at the current MCL level, based on olm.cfg. Emergency calls are not rejected at MCL 1–3,
but all calls, including emergency calls, are rejected at MCL4.
•
Tell the network to stop sending traffic—This starts when BTS is mildly congested (at MCL1) and
continues through all higher MCL levels until the overload condition abates to MC0. This action can
only be applied to the following types of networks:
–
SS7 sends Automatic Control Level (ACL) parameter in ISUP release messages.
–
H.323 sends Resource Availability Indicator (RAI) message.
–
SIP sends 500 or 503 with a retry.
•
CA stops sending triggers to POTS FS—When the FS is congested the following occurs:
–
FS notifies CA once of its congested status.
–
CA sends only emergency triggers to FS, as it manages FS’s congestion abatement
Slowing Overload Reduction
Sudden abatement reduction may cause MCL to rapidly increase again. To counteract MCL “bouncing”,
MCL reduces one MCL level at a time, regardless of how low computed MCL becomes. This permits
the system MCL to reduce gracefully over a number of intervals.
Damping also slows the system MCL. Damping values are in milliseconds and define the shortest
amount of time an MCL level can exist. You can configure the damping time for each MCL level in
olm.cfg using:
•
level_1_damping_time
•
level_2_damping_time
•
level_3_damping_time
•
level_4_damping_time
Configuring
This section explains how to perform the following tasks:
•
Setting the Minimum System MCL
•
Configuring the SIP Response Code
•
Configuring Emergency Call Handling
•
Configuring SIP Message Handling
Note
These tasks include examples of CLI commands that illustrate how to provision the specific feature. For
a complete list of all CLI tables and tokens, refer to the
Cisco BTS 10200 Softswitch Command Line
Interface Reference Guide
.