SIP Trunking

The concept of SIP trunking is a feature that has been supported in Communications Server since OCS 2007 R2. SIP trunking enables Lync Server to connect either to another IP-based PBX using SIP or to an Internet Telephony Service Provider (ITSP).

SIP trunking is generally used when integrating Lync Server directly with an existing IP-PBX from vendors such as Cisco or Avaya without the need for a media gateway device. Alternatively, it can be used to provide telephony service to Lync Server without the need for traditional PBX, media gateway, or wiring. Instead, an ITSP provides SIP trunking services across the Internet to allow Lync Server to make and receive phone calls using purely VoIP without a traditional phone infrastructure. It is also the method by which Lync Online users can leverage Lync for telephony functions.