A state of the art, extensible SIP Application Server
Zero-conf multiparty conferencing and WebRTC gateway


SylkServer is a SIP application server based on SIP SIMPLE Client SDK that can be programmed to perform SIP end-point applications. Examples of such server applications are conferencing, media offline storage, playing voice prompts, IVR, or gateway to other protocols like XMPP. The server supports SIP signaling over TLS, TCP and UDP transports, RTP and MSRP media planes, has built in capabilities for creating ad-hoc SIP multimedia conferences with windeband Audio, IM and File Transfer and can be easily extended with other applications by using Python language.


SylkServer is not designed to transparently route packets, authorization, accounting and handle NAT traversal for signaling or media. Performing applications like SIP Proxy, Registrar, or Presence Agent are out of its scope. SylkServer must be typically deployed behind a SIP Proxy for providing such functions.

SylkServer is horizontally scalable with the amount of available hardware by using SIP Thor, a P2P based self-organizing network technology.


SIP Signaling

  • TLS, TCP and UDP transports
  • XMPP Gateway


  • Conference participants
  • Wideband RTP mixer
  • MSRP switch

NAT Traversal

  • SIP Outbound Proxy
  • ICE clients
  • MSRP Relay clients
  • MSRP ACM clients

Voice over IP

  • Wideband (Opus, G722)
  • Narrowband (G711, iLBC)
  • SRTP encryption (SDES, ZRTP)
  • Hold/Unhold

IM & Presence

  • MSRP and XCAP protocols
  • CPIM envelope
  • Is-composing indicator
  • Delivery reports

File Transfer

  • MSRP protocol
  • Progress reports
  • Conference-info extension
  • Conference room persistent

Implemented Standards

The server implements relevant features from the following standards:

STOX IETF Working group

STOX IETF Working Group has been chartered to standardise SIP/XMPP protocol interoperability.

The feedback provided by SylkServer was instrumental in the standardisation efforts of STOX IETF working group, originally started by P. Saint-Andre.