SIP vs. PRI

For years businesses have utilized PRI for their voice communication.  Now SIP is becoming a more popular and PRI is being phased out.  Here’s a nuts and bolts comparison of the two technologies:

• PRI stands for Primary Rate Interface.
• SIP stands for Session Initiation Protocol.
• PRI is part of the Public Switched Telephone Network.
• SIP is Voice over Internet Protocol (VoIP).
• PRI’s are sold per circuit.  Each circuit provides 23 channels or call paths.
• SIP is sold per channel.  Providers might have minimums but that number is usually around 10.
• PRI is completely separate from a company’s internet or data circuits.  (There are integrated T1 circuits that utilize
• PRI technology but in this example we’re referring to PRI as a voice only circuit.
• SIP is typically sold with internet access, on a data circuit or as a part of a data network, like MPLS.
• PRI offer DID functionality.
• SIP works with DIDs and out of area DIDs, so a company is not limited to the phone numbers in its geographical area.
• PRI channels are static.  They sit dormant when they’re not in use.
• SIP is dynamic.  When SIP trunks aren’t in use, the bandwidth they ride on is freed up for data and other transmission.
• Multiple users at a given location can share the voice channels provided by a PRI.  If the number of call channels is inadequate, an entire new circuit would be necessary, which could take weeks to implement.
• Users, companywide, can share SIP trunks centralized at a company’s host site.  If the number of SIP trunks is inadequate, new trunks can be established in a few days.
• PRI requires a local loop, provided by the incumbent provider.  Phone service providers need an agreement with an incumbent to offer PRI, so PRI service has a more limited availability than SIP.
• SIP is offered by just about every phone service provider in the telecom industry.
• PRI requires the existence of a T1 card in a PBX or phone system.
• SIP requires a SIP gateway to connect to the public switched telephone network but can be engineered to work with any type of phone system.