Registration, DNS, and routing

Rooms

1. REGISTER and bindings

   REGISTER binds an address-of-record to one or more Contacts, and the registrar is a different role from the proxy.

2. Locating a server with RFC 3263

   RFC 3263 turns a SIP domain into a transport, a port, and an address with NAPTR, SRV, and A or AAAA.

3. Loose routing and Max-Forwards

   With lr, the Request-URI stays the remote target, each hop pops its own Route, and Max-Forwards of 0 yields 483.

4. Outbound, reg-id, and keepalives

   RFC 5626 binds a UA instance to one or more flows with reg-id and +sip.instance, and keepalives hold those flows open.

5. Path and Service-Route

   Path is the inbound vector stored with a binding, and Service-Route is the outbound vector the registrar gives the UA.

6. GRUU and a single instance

   A GRUU routes to one UA instance, and the registrar returns it as pub-gruu or temp-gruu on the binding.

7. Forking and early dialogs

   A forking proxy creates one client transaction per binding, and each To tag is a separate early dialog.

Ecosystem

SIP does not replace workforce management, quality monitoring, CRM, emergency policy, or a messaging registry. It is the session seam those systems hang from. Compliance notes on this page are educational and are not legal advice.

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