Call 0844 824 6664

What is the Difference - SIP and VoIP?

Sometimes, in fact often, questions get thrown around our office, there are so many acronyms out there that it is easy for someone to forget what PABX or PSTN or NC stands for in a product description. In general though we tend to know most of them and there is always someone to put us right if we forget one.

However there is always one discussion which ends up with a few shrugs and that is

"What is the difference between SIP ( Session Initiation Protocol ) and VoIP?"

The thing is that we sell VoIP phones, which I think everyone understands, but also we have phones which mention SIP or sometimes just IP and that can be confusing for the customer services and sales team just as much as it can for the customer trying to equip their business phone system with suitable telephones.

Here, partly for my own sake, and also with a view to helping anyone interested I will try to define the difference between VoIP and SIP :

OK, we used to use phones which were connected via the PSTN ( that's the public switched telephone network of course ) whereas now, with the advent of high speed broadband it is possible to make and receive phone calls using your internet connection - all phone calls over the internet are generically labelled as VoIP ( Voice Over Internet Protocol ). Possibly what is misleading here is that VoIP no longer is a "Protocol" but rather a blanket term for many protocols.



Well if you have two cans and you want them communicate with each other you have to determine how to connect them ( string/ fishing line, rope, metal cord ) and then consider the best way in which to transmit information over them ( morse code, speech, shouting ) - that is a protocol in essence and some of these are specific to certain companies or manufacturers. A good list of some of these Proprietary Protocols can be found here :

The main protocols used to connect and transmit VoIP calls are : Megaco H.248, MGCP, MIME, RVP over IP, SAPv2, SDP, SGCP, SIP and SCCP. So we see here that SIP is one of many ways in which to provide VoIP communications. But why then do we not ask ourselves about the other protocols? Why this fascination with SIP ?

Why SIP?

The most powerful thing about SIP is that it interacts intelligently with other protocols, meaning that it is an agile system which can adapt its signalling protocol to match that of the client system. Further it supports a range of applications and is fast, flexible, scalable and with multi service support. Further to this it is Open Standards which allows a mass of third party applications to be developed for it. This flexibility make it the obvious choice for manufacturers of systems and products. Hence, SIP, as a protocol is been used now by the majority of new Unified Communications equipment.

SIP is a part of the vast VoIP ecosystem which has many protocols and a myriad of functions, it has triumphed over more standardised protocols such as Cisco's H.323. That is not to say that it delivers a superior user experience in any way, rather that its flexibility makes deployment and development easier, quicker and cheaper.

More information can be found here though amusingly the article is currently preceded by the warning
"This article may be too technical for most readers to understand. Please help improve this article to make it understandable to non-experts, without removing the technical details.".

If you are interested in how SIP ( or VoIP for that matter ) could help your business communications then feel free to get in touch on 0844 824 6664 or check out some of our IP telephony products here :