SIP – The Flexible Friend

By Steve Walker, Managing Director

Steve Walker, Managing Director at Reading-based Avaya Business Partner IP Integration believes that it is wrong to consider that SIP trunks are a cheap alternative to ISDN30. Better, he says, to think of SIP trunks as being a great business tool providing tremendous flexibility.

According to Steve Walker the apparent price advantage that people assume SIP trunks have over primary rate ISDN is a bit of a fallacy when you take in to account the security required to really compare apples with apples. “Are SIP trunks a viable alternative to ISDN30? Well yes they are but only when you consider the application you are putting them in to, the connectivity or access you are going to use and the security needed for what is after all a data circuit being used for voice. “Would we recommend the use of DSL as the connectivity access for SIP trunks replacing ISDN30? Probably not, but we would consider DSL for ISDN2-based SIP trunk replacements.

“It’s the flexibility that SIP trunks provide for business that is the key to their continued and increasingly successful deployment as replacements for ISDN. Until the advent of viable and robust SIP trunks the only practical way for organisations to achieve location independence was to use the now discredited non-geographical numbering schemes, 0845, 0870, 0871 etc. With SIP trunks you can have, as IP Integration does, say an Edinburgh phone number without an office in Edinburgh and being answered at a location of your choice.

“SIP trunks also enable users to extend the returns on investments they have made in other technology-based solutions. Take a multi-site organisation with an MPLS network. Adding a secondary connection in the form of a SIP trunk to the cloud provides that user with voice and data communication over the same network. Of course you need to have the spare bandwidth but with capacities increasing and costs falling that should not prove a barrier to increase productivity being achieved.

“We believe that customers should look closely at the security aspects of SIP trunks. Any user with a connection to the web beyond basic DSL would have a firewall in place and SIP trunks should be no different; it’s just another internet connection which needs protection.

“IP Integration works with UM Labs to provide session border controllers (SBCs) at the customer premises to protect SIP trunks. We have tested this solution with suppliers such as Gamma Telecom and Telstra as well as with our major communications platform vendor partner, Avaya.

“Our best practice recommendation for SIP trunks is to install an SBC at the user premises. Whilst this does increase the overall cost of SIP trunk provision the customer is secure and for the reseller there is additional margin to be made from the SBC.”

A viable replacement for ISDN
Walker says that in the early days of SIP trunks it suffered from a lot of bad press but that today, if installed professionally, the product is a viable replacement for ISDN.

“It’s not an exact replacement however and anyone expecting a Skype-style free ride will be disappointed. Many communications providers and customers have tried to do SIP on the cheap and found to their cost that it just doesn’t work reliably. Customers using 50:1 or even 20:1 contended bandwidth with no QoS should not be surprised when the voice quality isn’t up to ISDN standards.

“SIP is not as generic as ISDN and to get it right, as I mentioned earlier, a security device which also provides a gateway between the network and the switch (the SBC) is essential. Communications providers and customers should expect to budget around the same for QoS-enabled bandwidth and the SBC as they currently do for ISDN circuits and associated PBX cards. If a customer has spare QoS bandwidth then SIP may provide a cheaper alternative, and if it is a greenfield site then savings can be made. However, I see the true benefits of SIP are as being;

Burstable capacity
Location independence
Detachment from tarnished NGNs
Larger apparent footprint/coverage
Disaster recovery and home worker support
Efficient use of existing connectivity

“One example of this would be Clara.net who have diversely routed SIP into two data centres to provide a resilient solution, with no ISDN in sight (though they do not use SBCs as they are the provider and trust their own network security).

“We have several other customers who have multi-site networks where disaster recovery is the main driver for SIP. Here thousands of DDIs can be automatically re-routed with the DDI preserved to alternate locations. ISDN just lumps them all together which is not great when you have 4,000 extensions all hitting the switchboard!

“For our contact centre customers the ability to increase and decrease channels almost instantaneously with only a one month commitment allows better response to peaks in traffic and major events/campaigns whilst reducing costs – no longer will 100s of ISDN channels lay idle for nine months of the year, draining OPEX budgets.”