ISDN rides off into the sunset as SIP trunking takes centre stage

ISDN was first defined in 1988, but soon it will be disappearing forever - maybe not before time, says Sonus's Kevin Baynes

The writing is on the wall for the UK's integrated services digital network (ISDN).

Starting this summer, ISDN will be in ‘sunset' mode as the phase-out programme starts in earnest - almost 30 years after this pre-WWW network technology was first defined.

Over a year ago, BT finally made the decision to shut down its ISDN network completely by 2025. This approach mirrors similar positions taken by telecoms companies in the US and across Europe.

The decision to shut down ISDN stems from the fact that more and more businesses are outgrowing their current communications networks and starting to demand increased levels of functionality.

While ISDN has a reputation for being a solid and reliable technology, it simply doesn't provide the features, flexibility and return-on-investment offered by session initiation protocol (SIP) trunking.

Furthermore, the fact that BT will cease investment in ISDN leaves business with an obvious choice: wake up to the advantages of SIP or be left behind.

Advantages of a SIP environment

In a nutshell, SIP enables enterprises to reduce costs, rapidly deploy new communication applications and solutions and seamlessly scale up or down as business demands.

One of the main benefits of SIP is that it combines voice, video and data all on from the same service provider's "pipe". Just one service provider means only one monthly bill and one person to turn to if an organisation needs assistance.

Additionally, because the infrastructure necessary for adding bandwidth for any new voice and data requirement is all in one place, as an organisation grows its service provider can provision additional bandwidth in hours rather than days.

Another key benefit of SIP is that phone numbers, which are traditionally associated with a building address, and more importantly a company's identity, are location independent. This means that even if you are in Manchester, you can still make and receive calls using a London number.

But before you deploy SIP, you need to make sure you have a session border controller (SBC).

Role of the SBC in SIP environments

While they excel at securing data, traditional firewalls are not built to deal with the real-time nature of SIP traffic. This means a SBC is a must-have when it comes to security for SIP-based communications deployments.

SBCs prevent communication-based denial of service (DoS) attacks through security features such as topology hiding, NAT [network address translation] traversal and encryption. The ability to do this prevents hacking and toll fraud, ensuring no nasty surprises at bill time or potentially a shutdown of service.

Securing your SIP communications system is vital, but an SBC also performs several other essential functions. For example, an SBC acts as the ‘interpreter' that enables different UC systems, SIP implementations, legacy phone networks and codecs to ‘talk' to each other. The SBCs ability to provide interworking functionality between legacy telephone networks and IP-based PBXs is vital for businesses that need to get the most out of earlier investments.

Finally, SBCs can also save a business money by helping to choose the most effective, least-cost route for sessions over a network.

SBC today, SIP tomorrow

With so many benefits, it makes sense to get ahead of the SIP curve by deploying an SBC today. That way your eventual migration to SIP will be simplified. When your business is ready to move, everything you need will already be in place. In the meantime, you will be saving money and can keep your ISDN for back-up.

This final question you need to ask yourself is how do I choose a SIP provider? The best advice is to read the fine print in the service-level agreement so you know what you should get in terms of network uptime, call completion rates and quality score.

Kevin Baynes, is UK & Ireland country manager for cloud-based SIP and 4G solutions company Sonus