Making the move from PSTN to SIP trunk: SIP trunking explained

The trusted old PSTN is coming to an end. Be it Analog, ISDN BRI, E1 or t1 lines, telephony is moving from PSTN to much more modern and flexible SIP trunks.

The big Telecom providers are fast phasing out the old PSTN functionality and are coaxing and forcing customers to move their telephony to IP. And so a SIP trunk and a phone system upgrade in the near future is going to be inevitable.

Verizon has stopped offering customers ISDN basic services. In the UK, ISDN lines are down to 3.3 million lines, from 4.7 million lines in 2007 and the trend accelerating. By 2017 major telcos such as BT, German Telecom will no longer offer ISDN lines.

As a result Session Initiation Protocol (SIP) trunking rose 50 percent in 2013 from the prior year, driven primarily by North America; EMEA is projected to be a strong contributor in 2014. But the move to a SIP trunk is very beneficial for a company. This guide explains what SIP trunks are, their advantages and how you can make the move.

What are SIP trunks?

Essentially, SIP trunks are telephone line trunks delivered over IP using the SIP protocol. Using this standard protocol, telecom service (VoIP) providers connect one or more channels to the customer’s PBX. Phone numbers and DIDs are linked to the SIP trunk. In many cases numbers can be ported to the SIP trunk.

Benefits of SIP trunking

But our farewell to the PSTN will bring companies many benefits. SIP trunks will deliver:

• Lower monthly Line & DID Rental– The monthly fee to have a number of lines installed at your office drops significantly with SIP trunks. Simillary DIDs cost a lot less
• Lower call charges– there are many SIP trunk providers and competition has driven down call charges significantly. Some SIP trunks even come with unlimited calls
• Better customer service– Provide better customer service by adding more geographical & international numbers. Just by adding numbers to your SIP trunk and terminating them on your IP PBX you can give customers more options to dial in, at a significantly lower cost. Reduce the barrier to contact you and increase sales
• Move offices and keep the same number. SIP trunks are not bound to a location, so its easy to move offices without having to change your stationary or inform your customers. No need to hassle and pay a telco to divert phone calls.
• Maintain better business continuity– for example, if an office is temporarily re-located in an emergency, SIP trunking makes the process quicker and easier
• Eliminate VoIP Gateways– SIP trunks will eliminate the need to buy and manage VoIP Gateways. All phone calls come in via IP. No extra conversion often means better quality too
• Leverage a modern IP PBX– Modern IP PBX / Unified Communications solutions will give customers increased productivity, mobility and boost sales. Connecting an IP PBX to SIP trunks is much easier than via the PSTN.
• Flexibility– it is easy to add channels to your SIP trunk to cope with increased calls. A simple phone call will allow you to add channels, and often this can be done immediately. Compare that to getting additional lines installed and then having to upgrade your old PBX to handle more lines!
• Correct number of channels– With SIP trunks you can easily choose the correct number of channels that you need, whereas with ISDN/T1 you often have to choose to add either 15 or 30 lines. This usually means you end up with expensive extra capacity.

Selecting the right SIP trunk provider

The next step is to choose a SIP trunk provider who will supply the necessary SIP trunks. A few factors come into play when making this decision:

• Security - As SIP trunks are exposed to the internet its very important that the SIP trunk has a well secured network and has an anti fraud system in place. The anti fraud system must monitor the system and provide protection against call fraud.
• Own network – Does the SIP trunk provider run their own network or is it a rebranded service? There are quite a few providers out there reselling SIP trunks from other providers. Select a provider who has control over their service & network.
• Competitive Cost– Costs vary widely between services. Some vendors will overcharge for SIP trunks. Look for competitive rates, but ensure that you are getting business quality SIP trunk service. For example, telecom providers will provide a cheaper quality to internet call shops. Be cost conscious but expect to pay a bit more for business class service.
• Number Porting– Can the provider port your phone numbers? Ensure that you choose a provider who can port all the existing numbers – not all providers are able to do this for all regions.

Upgrading the internet connectivity

Once you have selected your SIP trunk provider, consider a dedicated internet line for the SIP trunk. Most firewalls are able to handle multiple WAN connections, and considering the low cost of an internet line in most places, a separate VoIP connection will be the most reliable way to ensure the quality of your VoIP calls. However, some SIP trunk providers bundle their service with a dedicated internet line already.

This keeps your voice traffic separate from your data traffic. Much will depend on the cost and your network infrastructure. Check that your firewall is up to date and will be capable of handling VoIP traffic correctly.

Upgrading the pbx to an IP PBX

Chances are that the trusted old PSTN lines are connected into another trusted old device, the PBX. This device its inflexible, difficult to manage and often expensive. Technically it is possible to buy a gateway that allows the old PBX to talk to the SIP trunks. However now is the time to upgrade to a modern IP PBX and leverage the flexibility and modern features IP telephony can bring. There are may reasons to do ranging from cost savings, to productivity increases right to boosting sales. More about that here. Once the decisions has been made you’ll have to decide for the type of IP PBX. Your choices are hosted, an appliance or software based.