Common UCM Service Parameters to change

It can be beneficial for candidates sitting the CCIE Voice Lab to change several UCM Service Parameters in one visit to the list of Service Parameters in the UCM Administration pages. Below is a list of parameters one could consider changing without causing too much damage (and are parameters you might well change in the real world). Some/all of the service parameters listed may not need to be modified and there are others which are obviously not listed here that may be required to be modified. Take that as the IPexpert disclaimer!

The list of service parameters are shown with the default values- so you would need to modify these parameters to be different from the screenshots.

It is often useful to generate CDR’s for all calls made through the UCM- even for calls that were never completed successfully. In this instance you would need to set the first two parameters to “True”. Ok that might be a fairly lame start to proceedings but the third one listed above is very useful when using trace files and/or the DNA tool for troubleshooting call routing issues (set to TranslationPatternandAlternateAnalysis).

T302 is the interdigit timer and would be used typically for international calls when the end of string “#” character has not been used. 15 seconds is too short and hence this parameter is commonly modified (7 seconds – 7000 milliseconds) sounds reasonable.

It is a pain in the assertive part of your brain to keep on pressing the transfer softkey twice when transferring callers to another extension. When the above parameter is changed to “true” is is possible to press the transfer softkey, dial a number and hang up (as opposed to pressing the transfer softkey for a second time).

When UCM specifies G711 as the codec to use when initiating a call to gatekeeper it asks for 128kbps of bandwidth in the ARQ message. GK resolves the destination number and UCM begins H225 and H245 communication with the destination gateway. It might be that the codec negotiated is g729. The UCM would need to send a BRQ message (BRQ Enabled=True) by modifying the amount of bandwidth required from 128kbps to 16kbps otherwise there could be a situation whereby enough bandwidth for g711 is provisioned but the active codec is g729 thus unnecessary calls.

Sticking with H323 > gatekeeper, the UCM will use an ephemeral port number for H225 signaling. You are able to tie down the port number to 1720- useful when using the “alias static” command on gatekeeper.

The first parameter listed above is useful to avoid CFUR loops- set this to a value of “1″. The Call Forward All setting on the DN’s configured within UCM will all need a CSS assigned in order for the Call Forward All to be successfull. Other Call Forward (such as busy/noans) derive the CSS from the LINE/DEVICE concatenation bit CFA does not unless you change the second service parameter above to “Use Activating LINE/DEVICE”.

The service parameter above needs to be changed to “False” if you are using H323 gateways which report a Release with “unallocated number” cause code when the POTS interface has layer 1/2 problems. If the flag in the service parameter above is not changed to False (True is the default) then call routing will cease and any backup path will not be used.

7965 phones advertise G722 as the preferred codec when g711 is selected as the region codec to use. If you are told to use g711 within a site then you would need to disable g722 advertisement.

When Locations CAC/RSVP CAC blocks a call from completing over the WAN, you may want to enable AAR.

When H323 gateways are being used you probably want calls through the H323 gateway to survive when connectivity problems are causing keepalives from being returned to SCCP phones. In addition to changing the above service param to “true” you would need to enter the “call preserve” command within voice service voip > h323 IOS CLI.

Vik Malhi – CCIE #13890
Managing Partner / Instructor – IPexpert, Inc.

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