TAPI Service Provider for SIP


TERASIP is a TAPI Service Provider (TSP) for Microsoft Windows which offers support for the SIP protocol. The use of TERASIP allows users to make SIP calls through existing TAPI applications and thus connect to SIP telephony providers or directly communicate with others (PC to PC) using the SIP protocol.


SIP Protocol

  • SIP stack compliant with RFC 3263 - Session Initiation Protocol
  • Supports client registration and authentication at SIP proxies
  • Provides registrar server interface
  • Supports DTMF generation and detection through RFC 2833 (RTP) and  RFC 2976 (INFO message)
  • Supports UDP, TCP and TLS Transport
  • Full DNS NAPTR and SRV support
  • Supports STUN for NAT traversal
  • Operates on multihomed systems


  • Supports multiple instances (modeled as TAPI lines) bound to different local IP addresses and ports
  • Supports multiple SIP provider configurations (proxies or direct), modeled as TAPI addresses
  • Supports direct calling mode (PC-to-PC or DNS SRV record lookup)
  • Supports full SIP URIs as well as partial URIs built depending on the following address types:
    • Phone Number
    • IP Address
    • E-Mail Name
  • The following TAPI operations are supported: lineAnswer, lineMakeCall, lineDrop, lineGenerateDigits, lineMonitorDigits, lineHold, lineUnhold, lineBlindTransfer
  • Supports Server-Side transfer (tells an application when the remote party has issued a REFER)
  • Optional: Registrar Interface for handling Client registrations
  • Optional: Authentication handling of client requests
  • New in version 1.3.0: lineSetupTransfer, lineCompleteTransfer, lineSwapHold 


  • Supports audio media streaming through TAPI3 compliant Media Service Provider (MSP)
  • Comes with its own DirectShow based RTP stack
  • Offers support for the following audio codecs:
    • ITU G.711 µ-Law
    • ITU G.711 A-Law
    • GSM 6.1
    • iLBC 20/30ms (iLBC Website)
    • Speex 8kHz, 16kHz (wide-band), 32kHz (ultra-wide-band) (Speex Website)
  • (planned) automatic gain control (AGC)
  • (planned) Voice Activity Detection (Silence compression)
  • (planned) Acoustic Excho Cancellation (AEC)

Quality of Service - IP QOS

  • TERASIP supports QOS for RTP traffic in three ways:
    • Outgoing packets are prioritized by the Windows Qos Packet Scheduler
    • Packets are marked in the IP header for differential services (DiffServ)
    • Layer 2 network packets can be marked according to 802.1p
      (requires support from the NIC driver)

System Requirements

  • Windows 2000, Windows XP or Windows 2003  (x86)
  • New in version 1.3.0: Windows Vista, Windows Server 2008 (x86)
  • Network Adapter
  • Requires TAPI 3.0 or TAPI 3.1 for media streaming
    (TERASIP does not offer any wave devices at this time)
  • Can be used from TAPI2 applications (without audio), e.g. for Predictive Dialing

Supported Standards

  • RFC 3952 - Real-time Transport Protocol (RTP) Payload Format for internet Low Bit Rate Codec (iLBC) Speech
  • (planned) RFC 3711 - The Secure Real-time Transport Protocol (SRTP)
  • RFC 3550 - RTP: A Transport Protocol for Real-Time Applications
  • RFC 3489 - STUN - Simple Traversal of User Datagram Protocol (UDP) Through Network Address Translators (NATs)
  • (planned) RFC 3389 - Real-time Transport Protocol (RTP) Payload for Comfort Noise (CN)
  • RFC 3326 - The Reason Header Field for the Session Initiation Protocol (SIP)
  • RFC 3263 - Session Initiation Protocol (SIP): Locating SIP Servers
  • RFC 3261 - SIP: Session Initiation Protocol
  • RFC 2976 - The SIP INFO Method
  • RFC 2915 - The Naming Authority Pointer (NAPTR) DNS Resource Record
  • RFC 2833 - RTP Payload for DTMF Digits, Telephony Tones and Telephony Signals
  • RFC 2782 - A DNS RR for specifying the location of services (DNS SRV)
  • RFC 2475 - An Architecture for Differentiated Services
  • RFC 2474 - Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers
  • RFC 2327 - SDP: Session Description Protocol
  • RFC 3515 - The Session Initiation Protocol (SIP) Refer Method
  • RFC 4488 - Suppression of Session Initiation Protocol (SIP) REFER Method Implicit Subscription


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