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Why VoIP over VDSL is bad for business

VoIP over VDSL could spell disaster for UK businesses, warns Spitfire in its latest whitepaper

Harry Bowlby, Joint Managing Director - Spitfire
Harry Bowlby, Joint Managing Director – Spitfire

The whitepaper, entitled The Truth about VDSL and VoIP, examines the issues surrounding the use of VDSL circuits for voice over IP services.

VDSL (Very High Speed Digital Subscriber Line) or Fibre Broadband is widely established in the UK and is increasingly being used by businesses for high speed Internet access with download speeds of up to 80Mbps.

However, a broadband circuit optimised for Internet browsing is not necessarily the best choice for VoIP.

No guarantees

Although call quality on VDSL circuits may currently be acceptable, Spitfire discourages the use of VDSL technology for voice because it offers no guarantees of voice quality or any route to resolution should voice quality become unacceptable.

Spitfire explains that to give satisfactory voice quality, a circuit must deliver:

Spitfire issue warning
Spitfire issue warning

a maximum latency of 150ms end-to-end (mouth-to-ear);

packet loss of less than 1%; and

jitter of less than 45ms.

While these technical requirements may be met on a VDSL service most of the time, there is no guarantee that they will be met all or even some of the time.

Long lead times

Users wanting to upgrade to Ethernet connectivity for VoIP can be faced with deployment lead times of up to a year for Ethernet circuits. Poor quality voice calls in the interim could reflect badly on a business and damage its reputation.

Harry Bowlby, Spitfire’s Joint Managing Director, said: “Businesses that choose a VoIP solution without appropriate QoS guarantees are gambling with their future. Should voice quality issues arise, they may find that an acceptable solution is unavailable or takes an unacceptable period of time to deliver, leaving them unable to receive a business quality telephone service with a consequent materially adverse effect on their trading ability. VoIP over VDSL is a significant potential risk to UK business.”

Lower priority

The whitepaper points out that network usage is constantly growing, so the problem is only likely to get worse. At the moment, for example, priority over the public internet is given to streaming the explosive growth of digital TV services, such as Amazon Prime, NOW TV and Netflix. Other traffic may have to take lower priority as a result. With take-up of such services increasing, VDSL VoIP users should expect a deteriorating service.

So what should customers choose instead?

Spitfire offers customers its own Voice Approved Broadband circuits for VoIP SIP trunks. These ensure end-to-end call QoS, with guarantees on Latency, Jitter and Delay, both upstream and downstream. These guarantees are not available on VDSL broadband services.

As one of the few ISPs and fixed line operators to offer a SIP trunk service, Spitfire provides a complete end-to-end SIP service via its own IP and TDM infrastructure.

Graham Lewis, Spitfire Director IP Engineering and author of The Truth about VDSL and VoIP, said: “At Spitfire we discourage the use of VDSL for voice because, whilst anecdotally many people have found it ‘good enough’, it offers no guarantees of voice quality or any route to resolution should voice quality become unacceptable. Our reassurance of an end-to-end service with QoS guarantees has been a key factor in the success of Spitfire SIP trunks for VoIP.”

To download a copy of the whitepaper and find out about these issues in more detail, please visit:

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