Question 1

How many simultaneous calls do I need or get on a SIP trunk?

Accepted Answer

You need enough call paths to cover your busiest hour, and that number comes from your call traffic. Headcount doesn't set it. What you get is the lowest of several limits: the simultaneous calls your provider's plan allows, the calls your phone system and any gateway can handle, and the calls your data connection can carry. For a sense of scale, take 350 calls in the busiest hour at three minutes each. The standard traffic model puts that at 27 call paths for a target of one blocked call in a hundred.

Question 2

What is the difference between SIP trunking and cloud PBX?

Accepted Answer

SIP trunking connects a phone system you run to the public telephone network. A cloud PBX is the phone system itself, run by a provider on its own servers, with that connection built in. So the choice is about who operates the PBX. You either keep one and buy trunks for it, or hand call control to a provider and pay per user.

Question 3

What is the difference between SIP trunking and VoIP?

Accepted Answer

VoIP is a technology: voice carried over data networks using internet protocols. SIP trunking is one service built on it, in which a carrier connects a business phone system to the public telephone network over IP. A SIP trunk is VoIP, so the two are not alternatives. The question turns into a choice only when "VoIP" is shorthand for a hosted phone service, and then the difference is who runs the phone system.

Question 4

How does SIP trunking work?

Accepted Answer

A SIP trunk connects your phone system to a carrier over an IP network in place of telephone circuits. Each call has two parts. The PBX and the carrier exchange short SIP messages that set the call up, and the audio travels as a separate stream of packets until one side hangs up. The carrier passes the call on to whichever network serves the number you dialed.

Question 5

What is SIP trunking?

Accepted Answer

SIP trunking is a service that connects a business phone system to the public telephone network over an IP connection. A carrier sells it, and it takes the place of the telephone lines that used to do that job. Your phone system keeps handling extensions, voicemail and call routing. The trunk gives it a way to call outside phone numbers and to take calls from them. The name comes from the Session Initiation Protocol, or SIP, which the two ends use to set calls up and end them.

Question 6

What is a SIP trunk channel?

Accepted Answer

A SIP trunk channel is the capacity for one call in progress on a SIP trunk. A trunk with ten channels can carry ten outside calls at the same moment, in whatever mix of incoming and outgoing the provider's plan allows. The channel is a limit the provider applies in its own systems. No wire or circuit is set aside for it.

Question 7

What is the difference between SIP trunking and PRI?

Accepted Answer

Both connect a business phone system to the public telephone network. A PRI does it over a digital telephone circuit with a set number of call channels. A SIP trunk does it over an IP connection, where the number of calls is a limit the carrier sets. That one difference shapes what you would notice as a customer: which port on your PBX the service plugs into, how you add capacity, and what the service depends on to stay up.

SIP Trunking