If a user of a SIPendpoint registered to an Expressway configure with only thecisco.

The SIP INVITE message is a request that initiates a session between two or more SIP endpoints1.

The SIP INVITE message contains a Request-URI, which specifies the destination address of the session1.

The Request-URI can be either a SIP URI or a tel URI1. A SIP URI has the format sip:user@host, where user is the username or phone number, and host is the domain name or IP address of the SIP server2. A tel URI has the format tel:phonenumber, where phonenumber is the global or local phone number3.

If a user of a SIP endpoint registered to an Expressway configured with only the cisco.com domain physically dials “6501”, the Expressway will assume that the user is dialing a SIP URI within the same domain, and append the domain name to the user part of the SIP URI4. Therefore, the alias presented in the SIP INVITE message will be 6501@cisco.com.

If the user wants to dial a different domain, they must enter the full SIP URI, such as sip:6501@example.com4.

If the user wants to dial a tel URI, they must prefix the phone number with a plus sign (+), such as tel:+65014.

References := 1: RFC 3261 - SIP: Session Initiation Protocol 2: RFC 3261 - SIP: Session Initiation Protocol 3: RFC 3966 - The tel URI for Telephone Numbers 4: Cisco Expressway Administrator Guide (X14.0) - Dial Plan Configuration