PRI uses a dedicated circuit-switched connection with a guaranteed quality of service to transmit up to 23 simultaneous calls. SIP trunking uses existing packet-switched data connections in a best-effort manner to make calls by virtually connecting a PBX to a carrier's SIP network and transmitting calls alongside other internet traffic without priority. A single SIP trunk is typically limited only by available bandwidth or concurrent call sessions rather than a fixed number of channels.

1. PRI vs SIP
PRI
What is PRI?
 PRI (Primary Rate Interface)is a physicalconnection tothe PSTN over a dedicated line that only
serves voice transmission.
 PRI uses a circuit switched model for making voice connections between people
 PRI has a guaranteed Quality of Service (QoS)
 A PRI is a single line (typically a T1 connection in North America) with 23 voice channels (and a single
data/control channel), that allows your business to hold 23 calls simultaneously. This is not always
equivalent to the number of phone numbers a business has. Your business may have 100 phone
numbers that are directed to come across a single PRI, however, you will only be allowed to hold 23
phone conversations at once.

2. SIP Trunking
 SIP (Session Initiating Protocol) Trunking is a virtual connection to the PSTN over a physical line that
is often shared over your existing data connection.
 SIP Trunking uses a packet switched model for making voice connections between people
 SIP Trunking is typically Best Effort
 Comcast SIP offers Qos to the ESG
SIP
 What is SIP Trunking?
 In short, SIP Trunking is a method of sending your voice connection over an existing data line, and
therefore is commonly referred to as VoIP (Voice over Internet Protocol).
 Remember
 SIP Trunking is nothing more than the virtual connection between your PBX and your carriers SIP
Network, over the already existing Physical Data Line.
 Your call goes out over the SIP Trunk, is treatedexactly like every other piece of data on that
connection and is not given priority over webpages, emails, or instant messages.
 Once it arrives at your carriers network over the SIP Trunk, your provider’s equipment knows where
to direct that call; this may either switch it over to the PSTN (so that someone with a regularphone
can receive the call) or perhaps send it to a PBX at another location. A single SIP Trunk is typically
limited only by the amount of bandwidth on your data connection, or in some cases, limited by the
number of “call paths”, Concurrent Call Sessions.