CUCM SIP: In what condition the call is re-route to the second RG or trunk?

[Tao Ren]

Hi folks,

In CUCM9.1, for a route list, I configure multiple route groups, and multiple trunks within one route groups. My question is, in what condition CUCM will re-route the call to the next trunk or next route group, in another words, CUCM will re-route call in getting what SIP messages? For example, 483 Too Many Hops, 480 Temporarily Unvailable, 404 Not Found, etc? Can I change that list, e.g. add more error codes?

Cheers,

[Suresh Subramanian]

Hi,

There are couple of CUCM service parameters to reroute the calls to next device in the route list based on the below cause codes.

Stop Routing on Unallocated Number Flag:	This parameter determines routing behavior for trunk calls to an unallocated number. An unallocated number represents a dialed directory number that does not exist in a Cisco cluster. Valid values specify True or False. When the parameter is set to True and a call that is being routed to a remote Cisco cluster through a route list is released by a remote Cisco CallManager because of the unallocated number, a local Cisco CallManager will stop routing the call to a next device in the route list. When the parameter is set to False, the local Cisco CallManager will route the call to the next device.
	This is a required field.
	Default:  True

Stop Routing on User Busy Flag:	This parameter determines routing behavior for trunk calls to a busy phone at a remote Cisco cluster. When the parameter is set to True and a call that is being routed to a remote Cisco cluster through a route list is released by a remote Cisco CallManager because a remote user (phone) is busy, a local Cisco CallManager will stop routing the call to the next device in the route list. When the parameter is set to False, the local Cisco CallManager will route the call to the next device.
	This is a required field.
	Default:  True

[Tao Ren]

Thanks Suresh,

I have found those parameters in Service Parameter Configuration. So does that mean, I can only change system routing behavior for receiving "404 Not Found" (stop routing on Unallocated Number Flag" and "486 Busy Here"? Then for other SIP error message, CUCM will not re-route to next device, e.g. 483?

Cheers

[Dennis Mink]

One of the things you can set to remove a SIP trunk as a viable option for routing calls is SIP OPTIONS Ping

you can set that in the SIP profile configuration.

[Tao Ren]

Thanks, I mean the SIP trunk is OK, however CUCM get 483 when making a call to a destination over SIP, and CUCM drops the call instead of re-routing to the next route group or trunk.

[Suresh Subramanian]

I don't think CUCM will reroute the call if it gets the error 483(Too Many Hops).

The Max-Forwards header limits the number of hops a request can make on the way to its destination. It consists of an integer that is decremented by one by each proxy that forwards the request. If the Max-Forwards value reaches 0 before the request reaches its destination, it is rejected with a 483 (Too Many Hops) error response.

we need to check who is setting the header "Max-Forwards" to 0 on the SIP messages.

//Suresh

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[Tao Ren]

Thanks Suresh,

Sorry for my mistake. CUCM actually get 480 Temporarily unvailable.

[Suresh Subramanian · Accepted solution]

Hi,

When the system initially presents a call to a member of a route list, Cisco Unified Communications Manager reroutes for all cause codes other than Out of Bandwidth, User Busy, and Unallocated Number. The value of the associated service parameters for the Cisco CallManager service determines the rerouting decision for those cause codes. The Clusterwide Parameters (Route Plan) grouping includes the Stop Routing on Out of Bandwidth Flag, Stop Routing on User Busy Flag, and Stop Routing on Unallocated Number Flag service parameters. You can set each service parameter to True or False.

After a route list locks onto a trunk, no rerouting occurs. The media connect time of the endpoints and the Stop Routing service parameters determine when a route list stops hunting for the next route group. When media negotiation begins, the route list or hunt list loses the ability to reroute.

Reference URL: http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cucm/admin/7_1_2/ccmsys/accm-712-cm/a03rp.html#wp1056634

//Suresh

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[Muhammad Al-Hussein]

Hello All,

I hope You are doing well :-)

Two important things:

1- The normal behavior of the CUCM when using SIP pinging OPTIONS to check the status of the SIP Trunk is to send with Maximum forwards of "0", so the far end will reply back by the release cause 483 Too many hops, and this is what the CUCM is expecting to know if the far end understands SIP or not.

2- When You go to System Parameters > Any CUCM > Cisco Call Manager > Clusterwide Parameters  (Route Plan) :::: "Advanced" will show You another option "Stop Routing on Q.931 Disconnect Cause Code", and this is a very powerful field, because You can set all the ISDN release cause (that are usually corresponding to SIP cause codes) that You want to stop routing based on, e.g. (1 16 17 21 22 28 34 63 127)

 

I hope that this helped :-)

Thank You,

Muhammad Al-Hussein