Difference between SIP and PRI

1. Session Initiation Protocol (SIP) : SIP stands for Session Initiation Protocol which is a method of sending voice over internet. It not only allows voice call it also allows instant messages, video chats, meetings, or other communications. It establishes connection over Internet Protocol (IP) network. It works as a signalling and control protocol which connects, maintains and disconnects communication sessions. SIP trunks are virtual and they don’t require any additional hardware to signal and control communication sessions like Voice over Internet Protocol (VoIP) calls. 2. Primary Rate Interface (PRI) : PRI stands for Primary Rate Interface which is a telecommunication standard. In Integrated Services Digital Network (ISDN), PRI is used to deliver voice, data, video transmission which is achieved through a physical line or circuit. It provides a digital access to Public Switch Telephone Network (PSTN). A PRI phone system is connected to the PSTN through traditional copper wire telephone lines and it is based on circuit switching for establishing connection. 
Difference between SIP and PRI :

S.No.	SIP	PRI
01.	SIP establishes voice communication over Internet Protocol (IP) network / internet.	PRI needs traditional PSTN phone system for its setup.
02.	In SIP, virtual connection through network/internet.	In PRI, physical connection through PRI circuit (copper line)
03.	In SIP calls are transmitted in data packet format through IP network.	In PRI, calls are transmitted through physical circuits(Traditional telephone lines) .
04.	It is sold per channel.	It is sold per circuit and 23 voice channels are provided under each circuit.
05.	New up-gradation takes less time means some hours to set up and function.	New up-gradation takes more time means several days or weeks to set up and function.
06.	To increase the scalability additional PRI lines needs to be installed.	To increase the scalability additional PRI lines needs to be installed.
07.	It is limited only by bandwidth.	It is limited by the number of traditional wired phone lines.
08.	It also provides very good call quality but if it is badly configured in network then it affects call quality.	It provides very good call quality as it is physically configured.
09.	SIP requires no additional hardware.	It needs each circuit to be physically connected via cables.
10.	SIP costs are lower than PRI.	PRI costs are 30-40% high per line than SIP.
11.	Call diversity across vendors is easily available.	Call diversity across vendors is expensive.
12.	It allows unlimited time and distance calling.	It does not allow unlimited time and distance calling. It charges additional for long distance communication.