Federated VoIP

Background

Federated VoIP typically refers to:

• Using ENUM to discover SIP and Jabber addresses associated with a particular phone number
• Federated SIP, Federated XMPP/Jabber, or some combination of the two
• Dynamically connecting from any one domain to any other domain without any pre-configured routing
• Using the user’s email address interchangeably as a VoIP/IM identifier (rather than forcing the user to have a Skype or IM address in addition to their normal email address)

Federated VoIP does not require any SIP trunks, intermediate VoIP providers, etc

Implementations of Federated VoIP

• Unlike email, Federated VoIP (both SIP and Jabber) participants typically refuse non-TLS connections. In other words, using TLS is mandatory
• Fortunately, both SIP and Jabber use the same type of certificates for Federated VoIP, so only one certificate is needed
• Virtually all Jabber servers (for example, ejabberd) natively support the federation concept
• SIP proxies typically support federation, but TLS support varies. repro and Kamailio are the optimal ones.
• ENUM support is often an optional feature in SIP proxies, and it is not present at all in many Jabber clients
• Software PBXes (e.g. FreeSWITCH, Asterisk) are NOT SIP proxies or Jabber servers: they are typically not suitable for federated VoIP on their own. They should be used as application servers in conjunction with a dedicated SIP proxy.

Technical overview

OpenTelecoms.org has a good technical overview with diagrams

SIP proxies suitable for Federated VoIP

• repro from the reSIProcate project provides a quick and easy way to implement federated VoIP
• Kamailio provides extensive support for TLS, but it must be manually configured to work in a federated VoIP mode.

Jabber servers suitable for Federated VoIP

• ejabberd is by far the most common

Other aspects of a Federated VoIP deployment

It is highly desirable to provide all users within a Federated VoIP deployment access to a STUN/TURN server. The same STUN/TURN server will service both SIP and Jabber users:

• reTurn from the reSIProcate project
• TurnServer is another implementation of STUN/TURN

Provided that all phones/softphones support Internet Connectivity Establishment (ICE), STUN and TURN relay, the TURN server will ensure that users do not experience NAT problems.