SIP SIMPLE client SDK is a Software Development Kit for development of Real Time Applications based on SIP and related protocols for Audio/Video, Instant Messaging, File Transfers, Desktop Sharing and Presence. Other media types can be easily added by using an extensible high-level API.

The library has cross platform capabilities for Linux, Mac OSX and Microsoft Windows operating systems. The library should work with minimal changes on any platform that supports C and Python development environments. The SIP and media stacks are based on PJSIP/PJMEDIA 2.0 with patches required for the SDK advanced functionality applied.

To see SIP SIMPLE client SDK features in action you can try Blink or SylkServer


  • Multiple SIP accounts support
  • Full DNS support (NAPTR, SRV, A record lookup for all protocols)
  • Non-blocking, asynchronous, notifications based engine
  • Configuration framework
  • TLS Security for SIP signalling (SIP) and media (MSRP, XCAP)
  • Multiple media types per session (e.g. Audio, Video, IM)
  • Trace capability for all underlying protocols
  • Supports re-INVITE for adding and removing media

Privacy and Privacy

  • TLS for SIP signaling and MSRP media
  • SRTP for RTP media (audio and video)
  • SDES and ZRTP key exchange for SRTP
  • OTR can be added on top of MSRP streams

Supported media

  • Audio and Video (RTP)
  • Instant Messaging (MSRP)
  • File Transfer (MSRP)
  • Screen Sharing (VNC over MSRP)

All media types can be combined together in the same SIP session.

The library uses a separated from the core lookup mechanism for the next hop routing. This important feature allows the library to be used for building SIP clients that operate in combination with any SIP provider (by employing RFC 3263 DNS lookups), in a server-less LAN operation (using Bonjour protocol) or integrated into a network overlay developed by a third party (e.g. P2PSIP overlay).

Audio features

  • Conference Mixer
  • Wav Player and Recorder
  • Acoustic Echo Cancelation
  • Noise Suppression
  • Answering Machine


  • Ultra-wideband: OPUS 48kHz, Speex 32kHz
  • Wideband: Speex and G722
  • Narrowband: G711, iLBC, GSM

Video features


  • H.264 codec

Implemented Standards

SIP Signaling

  • SIP, Session Initiation Protocol RFC3261
  • SDP, Session Description Protocol RFC4566
  • An Offer/Answer Model with Session Description Protocol (SDP) RFC3264
  • Reliability of Provisional Responses in Session Initiation Protocol RFC3262
  • HTTP Authentication: Basic and Digest Access Authentication RFC2617
  • The Reason Header Field for the Session Initiation Protocol RFC3326
  • The Session Initiation Protocol (SIP) Refer Method RFC3515
  • The Session Initiation Protocol (SIP) "Replaces" Header RFC 3891
  • Session Initiation Protocol (SIP) Call Control - Transfer RFC 5589
  • Obtaining and Using Globally Routable User Agent URIs (GRUUs) RFC 5627

Address Resolution

NAT Traversal

  • SIP Signaling: Symmetric Response Routing Symmetric media RFC3581
  • STUN: Session Traversal Utilities for NAT RFC3489
  • RTP media (Audio and Video): ICE, Interactive Connectivity Establishment RFC5245
  • MSRP media (Instant Messaging and File Transfer): MSRP protocol relay extension RFC4976
  • MSRP Alternative Connection Model (ACM) RFC6135

Audio and Video

  • RTP, A Transport Protocol for Real-Time Applications RFC3550
  • Real Time Control Protocol (RTCP) attribute in Session Description Protocol (SDP) RFC3605
  • The Secure Real-time Transport Protocol (SRTP) RFC3711
  • Generation and parsing of RFC 2833/telephone-events payload in both RTP and SDP RFC2833
  • ZRTP Encryption RFC6189

Instant Messaging

  • Common Presence and Instant Messaging (CPIM): RFC 3862
  • Session Initiation Protocol (SIP) Extension for Instant Messaging RFC3428
  • MSRP Protocol RFC4975
  • Indication of Message Composition for Instant Messaging RFC3994
  • Message Summary Event Package RFC3842

File Transfer

Screen Sharing


  • Conference Event Package RFC4575
  • A Framework for Conferencing with the Session Initiation Protocol RFC4353
  • SIP Call Control - Conferencing for User Agents RFC4579
  • MSRP ad-hoc multi-party chat sessions draft-ietf-simple-chat