VoIP is the acronym for Voice over Internet Protocol. It means telephone services over Internet. Traditionally Internet had been used for exchanging messages but due to advancement in technology, its service quality has increased manifold. It is now possible to deliver voice communication over IP networks by converting voce data into packets. VoIP is a set of protocols and systems developed to provide this service seamlessly.

Here are some of the protocols used for VoIP −

• H.323
• Session Initiation Protocol (SIP)
• Session Description Protocol (SDP)
• Media Gateway Control Protocol (MGCP)
• Real-time Transport Protocol (RTP)
• Skype Protocol

We will discuss two of the most fundamental protocols – H.323 and SIP – here.

H.323

H.323 is a VoIP standard for defining the components, protocols and procedures to provide real-time multimedia sessions including audio, video and data transmissions over packetswitched networks. Some of the services facilitated by H.323 include −

• IP telephony
• Video telephony
• Simultaneous audio, video and data communications

SIP

SIP is an acronym for Session Initiation Protocol. SIP is a protocol to establish, modify and terminate multimedia sessions like IP telephony. All systems that need multimedia sessions are registered and provided SIP address, much like IP address. Using this address, caller can check callee’s availability and invite it for a VoIP session accordingly.

SIP facilitates multiparty multimedia sessions like video conferencing involving three or more people. In a short span of time SIP has become integral to VoIP and largely replaced H.323.