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What Is A SIP Trunk and Why Do I Need One?

What Is A SIP Trunk and Why Do I Need One?

It’s well established that VoIP telephony saves you money compared to traditional phone systems and we are often asked what SIP trunks are and why customers need to pay for them.

Let’s deal with myths first; there is still an enduring view that everything delivered via the internet is free and as VoIP calls are routed over the internet they are free. This is not the case! VoIP calls are made using a software PBX (private branch exchange) which is a software phone system that can be on site or in the cloud and switches calls between users on local lines while allowing all users to share a certain number of external phone lines. Using a software PBX means phone service can be delivered to users across the world via their internet connection and thus all internal point to point calls are indeed free wheresoever the user is.

Costs are introduced, and SIP become important once users need to make calls outside of their own soft PBX.

The Session Initiation Protocol (SIP) is a communications protocol for signalling and controlling multimedia communication sessions in internet telephony. Specifically, it negotiates routing the call across other networks and protocols allowing the call to be made to the dialled destination number. Clearly that internetwork traffic albeit initiated over the internet comes at a price especially if the destination is on the PSTN (public switched telephone network which is at least for now, the traditional phone system carried over copper cables) or on the cellular network (O2, EE or Vodaphone). SIP’s purpose is to provide a signalling and call setup protocol for IP-based communications supporting the call processing functions and features present in the PSTN (public switched telephone network). SIP has been extended for video conferencing, streaming media distribution, instant messaging, presence information, file transfer, internet fax and online games. Unlike other telephony standards SIP is distinguished for having been developed in the Internet community rather than in the telecommunications industry.

SIP trunks can be visualised as the virtual conduit for all your calls with channels allocated to allow for maximum numbers of simultaneous calls. SIP channels can be charged for including pre-paid calls or SIP channels may be simply allocated with calls metered in the traditional way; albeit at a lower rate compared to traditional point to point calling.

In summary SIP trunks are the chargeable element of the VoIP system that enable calls to be routed to other networks such as the PSTN or cellular networks. 


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