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• VoIPVideoAn...ntMessaging

Basic concept

• Where we talk about VoIP, we mean voice, video and IM, and also other solutions that use SIP or Jabber as a foundation (e.g. shared desktop, shared whiteboard)

• Just like everything else in FreedomBox, the VoIP solution helps users escape the cloud, keeping contact lists locally, encrypting comms by default, etc

User experience

• User can host their domain on the FreedomBox (DNS server)

• The same domain(s) and consequently the same email addresses can also be SIP and Jabber addresses

• The user can also have external SIP or Jabber accounts, and the FreedomBox can `register' with those external services (e.g. to receive phone calls from regular phones)

  • Users should be warned about the lack of privacy if they use legacy-style communications networks, but they shouldn't be prohibited from accessing such things
• The user can use any SIP or Jabber client in their home or elsewhere on the Internet.

  • Client devices may be softphones (e.g. Jitsi or desk phones like the Soundpoint IP from Polycom or mobile VoIP such as Lumicall)

• The client devices will cache contact lists on the FreedomBox in the usual manner for SIP and Jabber, and so the contact list will appear the same from any client

• Can dial regular phone numbers, and if the callee has a FreedomBox, be routed securely

• Optional: keeping voicemail messages on FreedomBox

• Optional: FXS sockets on the FreedomBox for connection of traditional analog telephones

• Optional/more advanced: full multi-user chat/audio/video conferencing server (e.g. SylkServer)

Technical features

• Use of ENUM to locate other ?FreedomBoxes (similar to sip5060.net and Lumicall

• Media stream encryption (SRTP and ZRTP) is typically supported from the client devices and not FreedomBox itself

• NAT traversal support: full ICE/STUN/TURN implementation on the FreedomBox

• However, if voicemail is required, FreedomBox needs to handle SRTP and ZRTP

• TLS (based on X.509) for setting up SIP and Jabber sessions

• Full support for federated VoIP RFCs for both SIP and Jabber

• Some kind of true `peer to peer' mode, such as
  • SIP RELOAD for SIP
  • Jingle nodes for Jabber

  • In particular, if the client device (e.g. a desk phone) has no support for Jingle Nodes or RELOAD, the FreedomBox will act as a kind of proxy for p2p communications. The client device will think it is just talking to a normal SIP or Jabber server.

Technical strategy

• Many of these things can also be implemented in Debian or on an OpenWRT device, so they are not unique to FreedomBox

Technical solutions

• reSIProcate and Kamailio are the leading SIP proxies for this type of thing

• ejabberd is a fully self-contained Jabber server

• Two TURN servers exist: reTurn from reSIProcate and TURNServer.org from the Jitsi community.

  • Both TURN servers work with SIP or Jabber clients
• some wrapper/install scripts and maybe web interface needed for setting up the certificates, inserting domain name in config files, etc

Privacy audit

• The more communications features that are supported, the more risk of privacy leaks
  • e.g. SIP headers contain clues about the user's client device (mobile or desk phone)
  • ICE attributes in SDP give clues about the user's local network topology and location

• Putting a media proxy (or rtpproxy) on the FreedomBox and forcing all traffic via the proxy is one solution

  • However, such solutions involve mangling the SDP, and that leads to ICE failures

  • Therefore, the FreedomBox might need to be a full SIP B2BUA

  • However, such solutions (with a B2BUA) make it harder to do end-to-end PGP authentication of the user identity, as PGP should be used to sign all the contents of the SIP messages
• More exhaustive analysis of VoIP privacy implications:

  • OpenTelecoms.org - A deeper look at VoIP Privacy

Related work

• OpenTelecoms.org aims to encourage VoIP based on open source and open standards

• Lumicall aims to provide a convenient and private communications solution for mobile VoIP

• Unified Communications on Debian provides a wider overview of VoIP features in Debian

• LibrePlanet has a project page for the FSF's high-priority project to provide a viable free replacement for Skype.

• WebRTC is a complete free open audio/video communication stack and protocols for the web, designed for web browsers and apps.

CategoryFreedomBox