ISDN vs. SIP – No Contest?

As more and more UK businesses outgrow their telecommunications solutions, they begin to look for an alternative that offers more flexibility, reliability and value for money. So does SIP outperform ISDN in all three areas?

The growth in the SIP trunk market has been one of the success stories of recent times and the pace of the market seems to show no sign of declining at the moment.

SIP continues to be one of our most popular topics at the Convergence Summit so the question ‘Who needs ISDN?’ is a hot subject.

Well, it seems a whole bunch of people still rely on ISDN as their main form of voice connectivity but increasingly users are turning to SIP. Why is that? What are the advantages? In fact, what are the pros and cons?


James Jeffs

We have spoken to providers to ask them what users are buying, what concerns they have and how they and their channel partners are converting ISDN to SIP with their customers before someone else does.

As more and more UK businesses outgrow their telecommunications solutions, they begin to look for an alternative that offers more flexibility, reliability and value for money.

So does SIP outperform ISDN in all these three areas?

Brian Iddon, Managing Director at Venus Business Communications says his company is seeing more interest in SIP from its fibre customers than any other telecommunication enquiry they receive.

“Customers come to us driven by a need for capacity to transfer and process data quickly, often exploring opportunities the cloud is bringing. Originally SIP trunks had a bad reputation for reliability, but the technology is sound. System integrators in the early days were deploying SIP over inadequate low speed internet connections. We see market demand for SIP growing particularly amongst the small and medium sized businesses that recognise the cost benefits initially and have confidence in the network removing high latency, the main reason for trunks dropping and packet loss. Customers then realise that there are a wealth of other benefits that SIP provides beyond cost savings that cement the decision to move from ISDN to SIP.”

James Jeffs, Director at Genius Networks says that compared to ISDN, SIP is cheaper on a per channel basis, more flexible in terms of what telephone numbers you can have and where you can have them, is quicker to install and can offer a very robust business continuity service that ensures your business never loses calls.

“SIP is also the natural choice for unified communications systems such as Microsoft Lync for when you need to extend voice connectivity outside of the office and into the public network. All clients are now requesting overlays with Lync for user presence and Instant Messaging, which creates more opportunities to upsell to the end user.”

Rob Smith, Technical Director, Siphon says that as a result of continued improvements in access connectivity over the past few years, SIP trunking is now well established as the preferred solution for small business and large enterprise.

“Concerns relating to quality and reliability that were raised in the early years of SIP trunking have been addressed and SIP trunking certainly delivers more flexibility, reliability and value for money than ISDN.

In terms of flexibility, SIP trunking enables a business to readily scale up or reduce the number of channels that are required, for example, in response to fluctuating seasonal demand. It also provides more options than ISDN when it comes to number plans. From a reliability standpoint, SIP trunking can greatly improve business continuity. When considered together with the SIP trunking costs (both for call charges and setup), these factors and the ability for an enterprise to be more flexible either in response to demand or the need to overlay value added applications, means that SIP trunking does indeed provide value for money.”

Are all SIP trunks the same?

Paul Wakefield, SIP Product Manager at Gamma says ‘Absolutely not!’

Screen Shot 2015-04-07 at 10.24.42“Although SIP itself is a standardised protocol, services vary with providers based on a number of factors.   A key focus will be the infrastructure on which the service sits with reliability and security paramount to concerns.  With Gamma’s position as a provider who own, manage and operate our own voice architecture leads to an excellent record of providing secure, reliable solutions.  Gamma Market research suggests that secondary would be the individual features and benefits provided. For example, Gamma’s call bundles and fraud management features are differentiators in the market providing a significant added value to keep us #1 in the UK.”

Paul Taylor of Voiceflex, also says no.

“SIP carriers will all be using different platforms, different SBCs, different data centres, different down line carriers, different ISP carriers, different portals, and will have different features. Cost is important, but one outage could wipe out your profit for the year.”

Jon Nowell, Head of Product Management at TalkTalk Business, agrees, “Simply put, SIP trunks are not the same. While they may broadly rely on similar protocols between providers, there is still much room to differentiate their offerings, for example cost, security and ease of deployment. It is easy to forget the customer in this debate – it’s time for customer centricity. We must all focus on the existing and emerging needs of the customer – be that cost reduction, scalability or things such as out of area numbering.”

Steve Harrington at Tipicall emphatically says, “Not all SIP trunks are the same at all. The underlying technology is the same but actually the services on top, location, technical connection and so on are very different. Our SIP trunks in Spain would be different to one of our competitor’s trunks in Liverpool for example. Some providers still use authentication as their main way of connecting which is not as technically sound as trusted IP. Resellers need to be careful when choosing a provider and they need to know what they are looking for.”

Are there real cost savings to be made?

Richard Buxton at Node4 says savings can indeed be made in many cases.

“In particular, we find that the majority of multi-site businesses can see significant savings from SIP trunking – especially through internal call cost savings (i.e. calls between branches being on-net).

However, bigger savings can be realised when customers centralise their telephony and aggregate their SIP channels. For example, a multi-site business can usually replace the ISDN lines at multiple locations with a centralised SIP trunk. Usually the total number of channels can be reduced as they can be aggregated rather than each site having to have enough channels for the peak requirement.

Additionally, there is an increasing number of customers who have deployed high bandwidth connectivity into their sites. They are able to utilise these connections to handle their SIP traffic alongside their data traffic – without having to install connectivity specifically for SIP. Converged Networks represent cost savings in most cases.”

“Potentially there are real cost savings to be made,” says James Jeffs of Genius Networks, “But this depends on how the client would like the service set up, i.e. a direct or indirect SIP service, and what they currently have in place.

If the client is still in contract with a carrier for their direct internet access and then adds the circuit and SIP channel pricing, the rental costs could in fact be more expensive. But if they are already using the SIP service provider for the data circuit then simply adding the SIP charges will be more cost effective than a traditional ISDN service. More savings can be made now that some carriers are offering free monthly calls per SIP trunk.”

Do the business continuity features of SIP stack up?

It’s a yes from Paul Wakefield at Gamma who says that as with all technologies there are areas of concern and sometimes disaster strikes, but the right solution can be built to achieve whatever business continuity requirement your business has.

“Gamma would always recommend a resilient build utilising multiple endpoints, multiple access routes and multiple hardware termination which provide a high availability solution on customer premise. Allied to this geographically diverse SBC clusters with the Gamma core network and the flexibility of IP routing in a highly meshed network can give as close to 100% uptime that you are likely to achieve.  If multiple endpoints simply aren’t an option, Gamma now offer the same geographical resilience and automatic failover solutions to our single endpoint builds.”

Brian Iddon at Venus says that one of the most important business continuity features that SIP delivers is complete independence with regard to location.

“Numbers are virtual, so once you have ported your number in to a SIP carrier it stays with you wherever you move. For modern day businesses wanting to make the most of their resources and capitalise on remote working this is a real boon.”

Business continuity is one of the main reasons many end users choose SIP according to Steve Harrington at Tipicall.

“It really works and if it is automated the customer should experience very little or no downtime. It must be set up properly and it must be planned correctly as there are so many ways to provide DR. The true cost of real DR does not have to be that high either as long as it is planned correctly.”

Is SIP trunk security adequately addressed?

James Jeffs at Genius Networks believes that SIP trunk security depends on how the service is set up.

“If the SBC (Session Border Controller) is deployed then a firewall-type service will be in place. Most carriers are now offering fraud alert services where you can limit the end user’s exposure should their service be breached as it will never allow the calls to go past a certain cost that you can set as a monthly total.”

“SIP security is a hot topic and flexibility is the key to the value of SIP as a product,” says Paul Wakefield at Gamma, “but there is a perception that other technologies are more secure primarily because it is an internet based protocol.”

He continues, “This is a myth, and SIP channels can provide a secure solution which, like business continuity, has a positive message surrounding it.  Call fraud is a major issue in the UK accounting for up to £900M per annum, and a key customer concern is bill shock, following a system hack.  Effective configuration and the use of specialist hardware such as Session Border Controllers can go a long way to securing a SIP service but Gamma also specifically includes a fraud management feature into their standard product to offer the ability to control exposure to such an incident, offering peace of mind and control to the customer.”

What about overlay services?

Overlay services offer an opportunity for resellers to both add value and at the same time increase average sales values.

For example, the telecoms cost economics for the UK Contact Centre market are massively changing according to Jon Nowell at TalkTalk.

“The good news is that the fantastic range of overlay services are allowing many contact centres to switch to SIP and utilise overlay features that surpass those available on ISDN.”

Paul Wakefield

Paul Wakefield

At Gamma Paul Wakefield says his company has an Inbound platform which compliments SIP trunks to provide a comprehensive service wrap, but such overlay services are beginning to enter the market as an enhancement to standard SIP trunks.

“Elements such as call recording, voice mail, intelligent DR call plans and other features are beginning to appear as network services, and this trend is set to continue and accelerate as service providers look to differentiate themselves from each other and align services to the trunk itself as opposed to separate platforms, the PBX or even hosted provision.”

Steve Harrington at Tipicall agrees with this model, “Overlay services are the next differentiators in the market. Call recording, DR, International numbers etc. are some of the services that have already been added and many more are set to come. Many are charged for whilst some are not. Resellers must make sure that their SIP provider has a roadmap for services that add real value to end users and not just services made up by techies for technical sake.

Ed Says…

So does SIP outperform ISDN for features, flexibility, reliability and value for money? The obvious answer is ‘yes, but…’ As seen here the ‘but bit’ is linked to the perceived or otherwise viewed reliability of the SIP bearer.  Even buts have buts however and the ‘reliability but’ is that the bearers are very reliable these days. Got that?!?



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David Dungay

Editor - Comms Business Magazine