When a new SIP packet arrives at Enswitch, the system needs to decide whether:

• The call is for it, or to be forwarded to an external SIP system. To do this, it looks at the domain of the SIP request URI. If it matches one of the local domains, it is routed by the system. If not, it is forwarded to the external system in the request URI.
• The call is from a local user or not. If it is, it should be authenticated, and then allowed to call any number its class of service allows. If not (for example it is from a DID provider), it should not be authenticated, but then must not be allowed to make chargeable calls unless forwarded by a customer's settings. If the domain of the SIP "From" header is local, it is assumed to be from a local user.

Therefore you should add a domain for any SIP domain your users' telephone lines will be using to connect to the system.

To add a new domain

1. Log in to the Enswitch web interface.
2. Go to System » Domains.
3. Click the "New" button.
4. Enter the following:
• The domain.
• Optionally a description.
• Which customer may use this domain in SIP addresses. If this customer has sub-customers, they may also use it, recursively.
5. Click the "Save" button.
6. Update your DNS server to send calls to this domain to the system. If you have an Enswitch cluster with multiple machines, use the Kamailio service address. You may use SRV records if you wish.