GNU SIP Witch is a service for the SIP protocol that is analogous to what Jabber does to XMPP, that is it offers registration, routing, and messaging between arbitrary SIP endpoints and resources. GNU SIP Witch was selected as part of the FSF initiative to replace Skype with free software, however there are additional opportunities that are very relevant to Ubuntu. SIP Witch can also be used as a local back-end to unify the telephony experience of desktop users in Telepathy and other desktop SIP user agents by automatically mediating access to local telephony resources such as SIP devices, desktop modems, gsm radio, idsn adapters, or local telephony servers, as well as remote VoIP service providers and enabling direct and secure call peering over the public Internet. The goal is to identify the work required to implement a flexible model allowing for an effective telephony experience for Ubuntu users.

Release Note

Desktop domain calling services will empower users to unify their telephony experience in new ways on Ubuntu. This includes creating and participating in secure calling networks over the Public Internet, as well as enabling access to both local and remote telephony resources and services in a unified client experience.


There is need to be able to use any resource that is available for communicating with people, whether a local modem device, an existing service provider, a private IP-PBX, or even directly in a secure manner using the public Internet, and to be able to do so automatically without requiring user intervention when situations such as connectivity to external services change.

To enable a complete telephony experience we can begin with unifying the client experience such as with Telepathy. For example, we want to begin with one universal contact for telephony be it a phone number or a sip uri, and a consistent manner for a single client to connect to said user with a single contact without requiring our users to determine where or how the call is actually placed, what service entry to use, etc. The user experience should be seamless, and hence the purpose of proposing a local mediating service for the SIP protocol.

User stories

User wants to run a simple phone system for several softphones they have at home, and dial them locally as extensions and have basic pbx features like call forwarding, multi-phone ring groups, etc.

User wants to call other users at remote locations. This might be by SIP uri or by a telephone number. Whichever use, it should not matter for the user to have to think about which profile or account to "use" and hence should be handled consistently from the client perspective regardless if the call is ultimately handed off for completion using a modem device, gsm radio, some SIP service provider, a local or remote IP-PBX, or the public Internet directly for secure URI peer to peer calling. Nor should the user need to consider which set of SIP settings for NAT issues are required based on who the user is calling and how the call is being completed.


We will be making use of existing SIP compliant softphones, many of which have already been packaged for Ubuntu. SIP Witch simply coordinates these devices in a local dialing plan, and offers uri routing that is resolved through DNS for calling remote users.

Since SIP Witch only mitigates SIP and will soon offer media packet forward RTP for SIP devices behind a NAT, while still establishing direct peer-to-peer communication between endpoints, it has very little overhead and no issues with patent encumbered codecs. Because peer to peer media connections are used between endpoints, sipwitch can operate directly with, manage, and scale "Social Key Verification" systems such as ZRTP. Since all users can use direct URI dialing to contact users at other locations there is no need for a central "service provider" or directory.

The primary feature is being able to run a SIP Witch "service" on Ubuntu, and this is a packaging issue alone. Exposing this service to management, that is, making it possible for ordinary human beings to in some even basic manner configure a SIP Witch installation for this specific mission at minimum without hand editing config files, and the completion of packet forward integration in the daemon itself, is the only Ubuntu-specific feature proposed for Lucid.



UI Changes

None anticipated for Lucid.

Code Changes

All upstream, noted in effort.


There is no data requiring migration.

Test/Demo Plan

Basic connectivity can be tested with sipquery command. It is possible a special test site could be created to test dialing to an external domain.

Unresolved issues

BoF agenda and discussion

From UDS Lucid:

"or why the desktop telephony user experience has been miserable so far"


FSF is trying to replace skype with a Free software alternative (sip witch):

Existing software:

Empathy is our default app for communication, we should figure out how to make that experience good

Usability issues:

SIP Witch: SIP Witch will take care of encryption and NAT and finding an available service. So we tell telepathy to just talk to SIP Witch.

Integration into Ubuntu One?


Action Items:

For Lucid+1?:

Specs/SIPDomainCalling (last edited 2009-11-30 20:38:15 by dyfet)