What is a SIP trunk?
A SIP trunk is the method by which voice services are delivered to your IP PBX. A SIP trunk routes your IP calls to and from the PSTN (regular phone network) instead of using traditional phone lines. The SIP trunk is provided down your broadband line (SDSL, ADSL etc.). For incoming calls, the SIP trunk provides a regular phone number in an geographic area code of your choice (e.g. London 020). You can have additional phone numbers for DDIs if required. Whereas with traditional phone lines you need one line to cover each simultaneous call (so your office might have 5, 10 or 100 individual lines) but with SIP trunks, all of your calls are send down a single IP feed. At the SIP Trunk provider's main hub all of your calls are separated out and forward to their correct destinations. The SIP trunk can be delivered down any broadband line, from any ISP.
SIP Trunk Quality & Reliability
Your IP telecomms infrastructure is only as good as its weakest link so once you have a great IP PBX, you need to have reliable interconnectivity with the outside world - that is your SIP trunks and your broadband connection. DrayTEL is our preferred and recommended supplier of quality SIP Trunks and DSL connectivity for the UK and Ireland. DrayTEL is UK based and their servers are all located in the UK. DrayTEL provides excellent call rates, inclusive call minutes and a multiply-peered highly resilient network to ensure the best possible reliability.
We mentioned earlier that you can connect your IP PBX to your SIP Trunk via any ISP and and broadband connection, however we also mentioned that your IP telecomms infrastructure is only as good as its weakest link which means if you take a great SIP trunk and then use a poor quality broadband line, that would affect your calls. Reliability, congestion, contention, obscure routing, infrastructure, bandwidth provision are just some of the factors which can affect your broadband and therefore voice call quality. Some broadband providers also add throttling and traffic shaping to deliberately vary or restrict your line capacity in real time. Even with a good quality broadband connection, your voice traffic is still subject to natural congestion, routing delays and packet loss which is part of the Internet (remember, the Internet is a public network and your data has to bounce around many nodes before reaching its destination). For data, that doesn't matter as much; data packets can be resent without you knowing and you usually won't notice speed changes, but with voice calls, it can have an immediate and apparent effect - loss of sound, 'dalek' voice, dropped calls etc.
The point of mentioning all this, is that whichever ISP you select, be sure that you use a reliable and well regarded one; one who assures you of excellent network quality and transmission consistency. Ask them about traffic shaping and contention. DrayTEL go one better than a reliable DSL line. The offer special DSL connections which bypass the Internet altogether to reach the DrayTEL server. These are called DrayTEL DSL trunks.
DrayTEL DSL Trunks
To avoid the problems mentioned above, as well as standalone SIP Trunks, DrayTEL provide DSL lines combined with SIP Trunks. A regular DSL line will take your voice traffic (data) and send it onto the Internet, combining it up with all other Intetnet traffic so you are fighting for bandwidth against every other Internet user, passing through many different networks on the way until your voice data reaches the SIP server.
A DrayTEL DSL Trunk is different; instead of your data passing over the public Internet, it is passed directly across to the DrayTEL gateway. It's "one-hop" to DrayTEL instead of passing through many different network and without fighting for bandwidth with every other Internet user. This ensures consistent quality and minimal latency (hop delays). You can actually also use a DrayTEL DSL line to send regular Internet data (web surfing etc.), in which case it's split off at your local telephone exchange (where the line terminates) and sent onto the regular Internet. DrayTEL DSL lines can also carry your VoIP traffic to alternative backup SIP gateways (non-DrayTEL) although without the benefit of 'one-hop'.
For full details of DrayTEL's SIP trunk and DSL trunk tariffs, Click Here.
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