Session Initiation protocol (SIP) is a virtual connection to the public switched telephone network and is used to signal and control communication sessions like VoIP calls. The capacity of a SIP trunk is equal to the capacity of bandwidth available between the customer and carrier.
Primary Rate Interface (PRI) is a telecommunications interface standard used on an Integrated Services Digital Network (ISDN) for carrying multiple voice and data transmissions between the network and a user. PRI is a high-capacity service carried as T1 or E1 trunk lines between telco central offices and your location. PRI comes in 2 flavours T1 and E1. A T1 line carries voice and data via 24 digital channels while E1 carries 32 Channels .It delivers multiple lines of voice and data into a business’s exiting PBX via one physical line.
SIP Trunking and PRI are two different ways of connecting your business to the PSTN (Public Switched Telephone Network). Typically PRI and SIP Trunking require a piece of an equipment in your office called a PBX (Private Branch Exchange). Most PBX can support both PRI and SIP Trunking connections, either directly or with support of additional component.