SIP Call Routing

When CUCM receives SIP INVITE message this is how it's being handled

*** LHS stands for Left Hand Side of SIP URI while RHS stands for Right Hand Side of SIP URI

Important Note: The Enterprise Parameter 'URI Lookup Policy' is set to case sensitive by default. This means that when CUCM receives INVITE message, it will make sure that the called alpha-URI matches with uppercase/lowercase. If this parameter changes, CUCM won't care about uppercase/lowercase.

Assume that the cluster has two Directory URIs, carlo@gmail.com which is local & Carlo@gmail.com which is remote. By default when the caller dials Carlo@gmail.com, CUCM will forward the call to remote cluster ignoring local directory URI due to case sensitive (assuming the SIP route pattern exists for route-string).

It's important to configure the following:

1. Cluster FQDN (CFQDN) Enterprise Parameter - This can be the FQDN of single node in the cluster or multiple nodes in the cluster separated by spaces. It can be a wildcard as well such as *.cisco.com
2. Top Level Organization Domain (TLOD) Enterprise Parameter - Single domain such as cisco.com
3. Enable "Use Fully Qualified Domain Name in SIP Requests" in the SIP Profile of all SIP trunks. When it will be used?
1. When LHS is numeric, the RHS of To header is always overwritten by the trunk destination (fixed in version 10 by making To header matching Req-URI) - You  need this setting
2. If the call is routed based on numeric LHS, the RHS of Req-URI header will be overwritten by trunk destination - You need this setting. If the call is routed by matching RHS against SIP Route Pattern, RHS of Req-URI is preserved.