Virgin Media is trialling a 200Mbps broadband service in the south of England, believed to be the fastest implementation of DOCSIS3 cable modem technology in the world. It sounds a lot faster than broadband services currently delivered over telephone lines, although that may be deceptive. Despite what the adverts might suggest, the Virgin Media “fibre optic” service is still delivered over a conventional coaxial cable and the capacity is shared within a neighbourhood.

The pilot service launched in Ashford in Kent and will build to 100 early adopters. Virgin Media will be testing services such as delivering video over broadband in full high definition and even 3D, as well as applications such as video conferencing and home security monitoring.

Virgin Media is working with Cisco to implement the pilot. The trial will run for at least six months and will help the company to understand potential consumer usage and to assess the commercial viability of offering such services.

“With the only true next generation network in the UK, we’re at the forefront of innovation and understanding when it comes to ultrafast broadband services and the 200Mb pilot will give us further insight into how true ‘wideband’ services might be used by consumers,” said chief executive Neil Berkett.

Virgin Media currently offers a 50Mbps service to some customers. The majority of its customers currently receive a 2Mbps service, which is being upgraded to 10Mbps.
In Japan J:Com aleady offers broadband at up to 160Mbps while CableVision in the United States offers up to 100Mbps using the DOCSIS3 standard.

Although Virgin Media consistently refers to its “fibre optic” cable network, it is actually a hybrid fibre-coax network. The main backbone is fibre, as with other networks, but the service is delivered to the home over a conventional coaxial cable.

Higher speed broadband is delivered by bonding together multiple radiofrequency channels to increase the bandwidth, but the total capacity of the cable is shared with neighbours. It is also asymmetric, meaning that downstream rates are higher than upstream.

For instance, a user on the highest 50Mbps tariff currently has an upstream rate of 1.5Mbps, while a user on a 10Mbps tariff only has 0.5Mbps upsteam.

Bonding 4 channels provides around 200Mbps downstream capacity with around 100Mbps upstream. That capacity is shared across a cable node, which might serve any number of homes in a neighbourhood. So in reality they will not all receive such rates at the same time. If they were all using broadband at the same time the effective rate would be a fraction of the headline figure.

Conventional coaxial cable television technology can continue to offer higher bandwidths by bonding together more channels, using capacity previously used for analogue television services, and ultimately by moving to an entirely internet protocol based architecture. In theory, coaxial cables could deliver many gigabits per second, but the capacity will always be shared with neighbours.

Virgin Media likes to point out that its cable technology, in its own simplified language, does not “slow down” the further a user is from the exchange. It does slow down the more people use the service, and the cable company actively manages traffic in order to serve its customers. Its current policies mean that a heavy user on a 10Mbps package might be throttled to just 2.5Mbps downstream and 128Kbps upstream at peak times.

Virgin Media is currently pushing the perceived advantage of its cable infrastructure over broadband services delivered over telephone lines. Limited trials of 200Mbps services make great headlines, but the reality is that most Virgin Media customers currently have no more than 0.5Mbps upstream and that can be throttled by 75% in peak hours if they are among the top 5% of users.

Conversely, broadband services delivered over telephone lines are indeed limited by the length of the line and they also tend to be asymmetric. They are also contended, in that less capacity is available on the backhaul network than the total capacity that is provisioned to consumers, typically at a ratio of up to 50:1, on the assumption that they will not all be using it at the same time. However, this is more of an economic consideration than a technical limitation.

In contrast, true fibre optic networks can currently deliver 1Gbps directly to the home, and such services are already available in countries like Japan. That is nowhere near the upper limit of their theoretical capacity, but most consumer equipment is unable to use higher speeds, at the moment. Furthermore, fibre optic networks can deliver symmetrical services, so users can send as well as receive data at very high speeds, and they are generally unaffected by other users of the network.