Rerouting Calling Search Space Phone Device vs Trunk

[tpfrankli]

I'm trying to understand when the Rerouting Calling Search Space is invoked and the impact on call routing. Here's a call flow Example:

PSTN Caller <--> ITSP PSTN <--SIP--> CUBE <--SIP--> CUCM Trunk <--SIP--> Cisco 8851 SIP Phone.

The Cisco 8851 is set to do a call forward all back out to a PSTN off-net phone number utilizing the same trunk that the call came in on.

Is the the Rerouting Calling Search Space on the Phone or the SIP trunk that is invoked for this call? The challenge I'm facing is I need to modify the ANI on the call to add in a STN phone number for Verizon so that I can send out the PSTN caller's caller ID to the off-net call forward all destination.

CUCM 10.5.2

IOS 15.4

Thanks

[Ayodeji Okanlawon · Accepted solution]

No,

The rerouting calling search space is used for REFER purposes. The RCSS of the referrer gets used to find the route to the refer-to target.

A typical example of rerouting css is used in SNR.

eg A calls B and B refers the call to C, then the reoruting CSS of B is used to route the call.

In your case this is just a normal call forwarding

[tpfrankli]

So I just tested and you are correct it was just the CFWALL CSS being invoked. Is it just SNR that would do Re-routing? I guess I'd like to know which CSS gets invoked and when. And what would be the purpose of having RCSS on a trunk?

Thank you.

[Ayodeji Okanlawon]

Personally I have never had to use rerouting CSS on a sip trunk. I have only used it for SNR. I am sure there are other case use for it, but I cant think of one right now.

[Vivek Batra]

Friends,

There are atleast two cases to use re-routing CSS on SIP trunk;

1. SIP trunk is pointed to third party server say Asterisk and REFER is received from Asterisk, in this case transfer target partition must be seen by re-routing CSS.

2. When CUC is integrated using SIP trunk and call is transferred from CUC (release to switch), then re-routing CSS must see the transfer target partition.

- Vivek

[Ayodeji Okanlawon]

Thanks Vivek (+5)

[tpfrankli]

Thank you that helps clear things up.