ISDN in retreat as SIP demand reaches tipping point

Lindsey McGowan, Product Manager, Azzurri Communications

The demand for SIP (Session Initiation Protocol) is on the rise, with IT increasingly beginning to eschew traditional ISDN channels.  SIP isn’t the new technology on the block anymore but its expansion has reached a tipping point, with growing confidence in its capabilities and the ever expanding list of benefits making a compelling business case.

Significant improvements in broadband speeds in recent times, and in particular upstream speeds, have been a real catalyst in kick starting the SIP market.  High speed internet is an essential component for ensuring a stable SIP connected network.

In the same way that the move from analogue to digital technology through ISDN offered quantum leaps in quality, recent advances in SIP technology now make it a truly viable alternative to ISDN.  Businesses are increasingly transitioning from legacy PBX (Private Branch Exchange) systems to IP-based unified communications platforms, and are investigating or rolling out SIP Trunking as a complementary technology.

So what are the benefits driving businesses from ISDN to SIP?

Cost savings are always a key factor in any enterprise technology decision.  And SIP Trunking can undoubtedly deliver real cost savings.

But it’s really the flexibility SIP brings to the table that will really sway organisations to make the move.  While reducing costs is not to be sneezed at, the operational benefits delivered by SIP around greater flexibility, disaster recovery and high availability which make a compelling case to say SIP Trunks have come of age and are hastening ISDN in retirement.

For distributed companies with multiple locations, SIP Trunking is an attractive solution. SIP offers organisations the ability to centralise their PSTN access and by consolidating and simplifying their infrastructure deliver considerable cost savings. When a new location is opened, you can add the branch to your LAN and route more bandwidth to that location to add the voice services.

SIP Trunking also enables organisations to only buy the capacity they need - meaning spending less money on telephony whilst getting the full end-to-end IP quality. SIP Trunking does not come, like ISDN, in two sizes for 2 or 30 channels, but can be flexed on a per channel basis to hundreds of channels per connection.  This makes it much easier to tailor to suit individual organisation’s needs, especially those affected by peak and off-peak seasonal periods.

Finally, SIP trunking offers business recovery features that are simply not available on more traditional telecommunications services.  SIP’s flexibility enables you to re-route your voice traffic in the event of any disruptions to locations or systems in an emergency.   You can also retain business critical numbers in the event of moving premises, without having to pay expensive call forwarding charges.

And what’s been slowing the take up?

If your PBX is SIP enabled, then the benefits in switching from ISDN to SIP are extremely compelling. If however, your business doesn’t have a SIP based PBX, then SIP should be something that you explore when your legacy PBX is due to be replaced (all modern PBX equipment will be SIP enabled).

Whether your business uses a Session Border Controller (SBC) is another factor to consider.  In my opinion organisations should always use an SBC to terminate a service provider SIP trunk onto their network.  An SBC offers essential security, demarcation, session management and interworking features that protect from denial-of-service (DoS) and other SIP-based attacks.  SBC’s also provides SIP trunk status monitoring tools.  An ISDN30 gateway discreetly offers these same services into a network, but when migrating calls from ISDN30 to SIP Trunking this security protection and controls lost without an SBC.

When looking for a SIP Trunking provider, you should always ensure you select a credible partner with a resilient infrastructure and watertight SLAs.   

Find out more

Azzurri delivers SIP Trunking solutions with a managed service wrap, covering IP connectivity, SIP Trunks, number management and SBC’s. We also offer organisations the flexibility to locate their PBX’s either at their sites or housed within our managed co-location centre.  Hosting within Azzurri’s datacentre means our customers don’t have to be concerned about space, power or engineering support. If you would like to find out more of this service, please give us a call on 0844 324 000 or email us at