VoIP over VDSL poses a long-term risk to business continuity despite many company leaders rating the technology as adequate, according to Spitfire's joint Managing Director Harry Bowlby who puts a spotlight on the potential pitfalls.
A lack of QoS guarantees for VDSL (Very High Speed Digital Subscriber Line) leaves businesses vulnerable to poor voice quality with no route to resolution, emphasised Bowlby. And users wanting to upgrade to Ethernet connectivity for VoIP can face deployment lead times of up to a year. The situation is set to worsen as more public Internet services such as Amazon Prime, Netflix and digital TV are prioritised. The answer, according to Bowlby, is a complete end-to-end SIP service run over a wholly owned IP and TDM infrastructure. "Businesses that choose a VoIP solution without appropriate QoS guarantees are gambling with their future," he stated. "VoIP telephony has numerous benefits in terms of cost savings, flexibility and functionality. But to provide a dependable VoIP service a high quality, reliable and secure online connection is vital."
VDSL technology has become widely established in the UK and is increasingly being used by businesses for high speed Internet access. With download speeds of up to 80Mbps it is not difficult to see why. However, a broadband circuit optimised for Internet browsing is not the best choice for VoIP. "To give satisfactory voice quality it is generally accepted that a circuit must deliver a maximum latency of 150ms end-to-end (mouth-to-ear), packet loss less than one per cent with jitter less than 45ms," noted Bowlby. "These requirements may be met on a VDSL service most of the time. However, they are not guaranteed to be met for all or any of the time. A 500ms delay on a web page is barely noticeable, but such a delay during a telephone call is clearly noticeable."
QoS is available on VDSL as a chargeable option. VDSL supports two types of services - Best Efforts and Real-Time. By default all traffic is Best Efforts meaning that in the event of congestion voice traffic could be dropped just like any other Best Efforts traffic. Real-Time QoS is an additional service that can be purchased for downstream VDSL. But there is no QoS mechanism deployed upstream on VDSL as this is not considered necessary because most web access involves download, not upload. However, a phone conversation is asynchronous and requires equal download and upload quality.
"No actual latency, jitter or packet loss targets are stated for VDSL Real-Time QoS, the service just offers to prioritise marked packets over others," added Bowlby. "In the event of poor voice quality on VDSL faults may be reported, but fault investigation is limited to the underlying broadband service. That said, VDSL is probably okay for now for many customers. It is considered by many to be adequate for voice based on how the wholesale network is currently dimensioned and performing. But in the future VDSL may not perform as it currently does in which case there are no guarantees to fall back on, because no contractual commitments have been broken."
Network usage is growing by the day and a big growth driver is television delivery over broadband with new service providers such as Amazon Prime, BT Vision, Netflix and NOW TV requiring assured data rates for their subscribers. "As this grows other traffic may have to take lower priority," said Bowlby. "High definition TV is already here and Ultra HD (4K) has been launched that uses 30Mbps per TV channel. As competition grows, to become a leader in the streaming TV market the national network will have to meet this new objective. Given the amount of money being spent on content for TV services Internet broadcasters will be keen to ensure that viewers on VDSL have priority access. As video traffic grows it will take priority over VoIP traffic and voice may get squeezed out resulting in call quality issues, which neither the end user nor the service provider have any recourse to resolve. So a critical consideration for customers should be, ‘if VDSL proves unsuitable over time can I swap it for another circuit that will work?'."
If in time a VDSL circuit proves unsuitable users may consider replacing it with Ethernet or complementing VDSL with a voice approved circuit. This is dependent on the supplier being active in the local exchange and whether there is spare capacity to provide the circuit. "It can take up to one year or more to install a new Ethernet circuit," said Bowlby. "During this time a business will continue to experience poor quality voice calls which may prove detrimental to the organisation."
Spitfire has tackled the issue head on with its own Voice Approved Broadband circuits for VoIP SIP trunks which assure end-to-end call QoS with guarantees on latency, jitter and delay both upstream and downstream. The reassurance of an end-to-end service with QoS guarantees has been a key factor in the growth of Spitfire's SIP trunks for VoIP. "Businesses that opt for VoIP solutions without QoS guarantees are storing up trouble," warned Bowlby. "VoIP over VDSL is a significant potential risk to UK business."