SIP (Session Initiation Protocol)

SIP (Session Initiation Protocol) is a signalling protocol used to create, modify and end IP communication sessions such as voice or video calls. It negotiates participants and parameters, while media commonly travels through protocols such as RTP; successful signalling therefore does not guarantee audio quality. A deployment may involve endpoints, a PBX, carrier, NAT, DNS and security controls with separate responsibilities. Design should address authentication, compatible encryption, fraud, numbering, codecs, ports and failure behaviour. Session border controllers, firewalls and call policies can reduce exposure but require correct configuration. Testing should cover inbound and outbound calls, transfer, caller identity, two-way media, emergency calling where applicable and recovery after loss of connectivity or provider service.