Speed of light

The ever increasing demand for network bandwidth is leading to the adoption of new technologies, such as gigabit over copper and optical Ethernet, which can accelerate dataflow both within local area networks and across towns and cities

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By  Neil Denslow Published  July 30, 2002

I|~||~||~|The growth of bandwidth intensive applications and the expansion of file sizes is putting an increasing strain on the network. Emerging technologies, such as Gigabit over Copper and optical networking, are allowing the capacity of networks to grow to meet this bandwidth demand in both local area networks (LANs) and metropolitan area networks (MAN).

The increasing strain being placed on networks can be easily seen by looking at the growth in e-mail usage or the increased complexity of everyday business functions, such as presentations.

“A few years ago, people were receiving five e-mails a day, now it’s more like 60 a day. You just have to think about the average number of e-mails to see the growing demands on networks. Also, look at the size of files. Five years ago a presentation was 100 K/bytes, possibly 10 M/bytes. Today we often have presentations of 40 M/bytes or 60 M/bytes,” says Stanislas de Boisset, network consultant, 3Com

Traditional copper technologies are unable to handle this dataflow, especially for distances of more than 100m, and the speeds achievable pale against those of optical fibres. For example, Copper can support 20 M/bit/s up to 500m, while fibre optics can already handle 1 G/bit/s up to 80 km.

The growing demand from desktop applications is forcing the use of optical fibre in businesses’ campus backbones and in buildings’ riser backbones. Matias Peluffo, technical director for connectivity solutions, EMEA, Avaya, explains that as a ‘rule of thumb’ the backbone needs to have 10 times the capacity of the horizontal layer to deal with the dataflow. With users now demanding 1 G/bit/s, only a fibre backbone can handle the 10 G/bit/s needed to support this.

“That’s where the move towards 1 G/bit and then 10 G/bits is really prompting the deployment of fibre optics in the enterprise backbone,” notes Peluffo.

Fibre optics are able to handle this greater dataflow because they transmit light rather than electrical signals. Light travels much faster than electrons and, because photons don’t interfere with each other in the way electrical signals do, it is possible to push more signals down a single cable.

The key to the system is the optical fibre, a narrow thread of glass — really pure silicon dioxide — wrapped inside a casing made of another glass with a different index of refraction. A light signal is then generated at one end of the central fibre and, because it reflects off the sides of the fibre as it travels along the cable, the signal doesn’t disperse or scatter. However, impurities in the fibre mean that some of the light will eventually be absorbed, causing signal degradation. Repeaters therefore receive a signal and amplify it before sending over the next stretch.

There are two main types of optical fibres, single and multimode. The difference is that multimode fibre is slightly thicker, 60-microns compared to nine, which means that it can carry more ‘modes’ or signals at the same time.

Peluffo says that multimode fibre is most often used inside buildings for LANs, as it can carry multiple signals at the same time, thus allowing it to support a number of users simultaneously. Also, because the signal only has to travel a short way, up to 300m, there it little pulse spreading so the effects of dispersion are unimportant.

Single mode fibre is used for longer distances of up to 70 km. As the fibre is narrower, it can only support one ‘mode’ at a time, which greatly reduces the amount of pulse spreading compared to multimode fibres. Dispersion can still occur, but this is counteracted by the glass chemical composition of the glass.

The speed of the cable is driven by the endpoints, either LEDs or lasers, which generate the light signal. This means a 500m cable running, for example, 100 M/bit/s can be easily upgraded to 1 G/bit/s, just by switching the endpoints.

“Essentially, the biggest differentiator between optical and non-optical is the accessibility of bandwidth and the possibility to turn that bandwidth up very quickly,” states Stefan Olofsson, consulting engineer, Cisco Systems.

Despite these advantages, Ravi Mali, director of networking division, Alpha Data, questions the assumption that a company needs to use optical networking within a campus. Instead, he suggests that cheaper Gigabit Ethernet technology can handle most enterprises’ requirements.

“Within the campus, the issue is that a lot of [networking] can be done using pure Gigabit Ethernet. The justification for laying an optical network to carry the data for an enterprise is very bleak, as the price point of Gigabit Ethernet is definitely lower,” he explains.
Gigabit Ethernet can be a particularly effective solution if a campus runs voice over IP as well. Mali explains that this removes the need for an ATM backbone, but still allows the integration of voice, data and video over IP. The organisation will also probably be able to draw on its existing skill sets to manage the network.

“Usually, a network manager is much more comfortable with technologies like IP and data over voice, which is [already] running on his network. When he comes to optical, he has to start learning completely new things,” he explains.

Optical is also unlikely to make a wide scale breakthrough into the LAN environment anytime soon. It is now possible to run 1 G/bit/s over Cat. 5 copper cabling up to 100m, which is sufficient for most desktops and servers.

“Wherever users connect their servers or their backend systems, that is where Gigabit over Copper is being deployed, and that’s where it makes sense to deploy it,” says Mali.

de Boisset agrees and notes that “many people still think that fibre will solve all the problems… If it is for LANs and you have distance between switches or PCs of less than 100m then definitely use copper because it will be far cheaper for you.”

||**||II|~||~||~|Optical fibres are therefore currently being reserved for long haul use or across towns/metros. Within the Middle East, John Steel, COO of support services for Batelco, says that every country now uses fibre for long haul at least, and a growing number are introducing it into metro areas as well.

MANs can be effectively created with just a few rings of fibres. New drop off points can then be easily added, even in a production network. After the drop off point, any service can be easily added on, from lowband Internet to DSL or Ethernet.

“Once you’ve crossed that hurdle and have fibre in place, you can do it very quickly,” suggests Cisco’s Olofsson.

The use of fibre MANs would potentially benefit a company with multiple offices, as the greater bandwidth would allow them to quickly send data between buildings and consolidate resources, especially in terms of their storage requirement infrastructure.

Traditionally, Synchronous Digital Hierarchy (SDH) or asynchronous transfer mode (ATM) has been utilised for long haul and metro use, but this is now starting to be replaced within MANs at least, by Ethernet. Neil Rickard, research director, Gartner Group, says that because this is considerably cheaper and easier to manage than SDH, private companies are laying their own fibres.

“Organisations are starting to obtain their own fibres between different locations on which they can run Ethernet technologies directly between LAN switches as they would if those switches were on two different floors of the same building,” he explains.

Within the region, Emirates Group had laid fibres in this manner at Dubai International Airport, and the Hyatt Group uses dark fibre from Etisalat to connect their properties in Dubai as well.

However, this model is a long way from taking off more widely in the region, primarily because of the position of the incumbent telcos. They still retain a monopoly on laying cables across public lands and Rickard says that they are usually unwilling to do so unless pushed.

“The telcos are keeping a firm control on things and you can only [lay cables] if you have enough leverage to get them to do something they are otherwise reluctant to do,” he says.
In practice, this means that only government bodies and the most influential companies have been able to utilise fibre in this way.

||**||III|~||~||~|Elsewhere in the world, the process of laying fibres has been accelerated by specialised companies, which lay fibres themselves and then rent them out to business.

Within the Middle East, this model has been prevented by the telco monopoly. Steel says that Batelco never lays cables for private companies to run and own themselves.

However, he suggests that the monopoly on laying cables may soon end as part of the wider liberalisation of the telecommunications sector.

Even if it does become possible for private companies to lay cables, they should not have to do it themselves. Instead, Rickard suggests that it is being forced on companies by the service providers’ unimaginative response to the spread of Ethernet.

“Except in the US, where there are a number of interesting Ethernet services at attractive enough prices to make it compare favourably with setting it up yourself… there are very few services that are actually more attractive than buying your own fibre,” he complains.

Within the region no telco offers any Ethernet services. However, Batelco is currently running trials and expects to introduce it into MANs within the next year. Steel says managed Ethernet services for businesses will follow on from this.

Despite the advantages that Ethernet MANs would offer, Olofsson questions whether there would be much demand in the region.

“If you go to a big city in Europe, there will probably be a number of corporations that have mainframe centres and if they can share their fibre channel and do distributed storage, then that’s a big [cost saving] for them. But we don’t tend to have that here,” he notes.

Peluffo though suggests that the growing use of Ethernet in MANs elsewhere in the world may also boost the uptake among enterprises within the Middle East. As Ethernet spreads, costs will decline and reliability will increase as global demand leads to standardisation and high volume production.

“This will result in an advantage in terms of availability and cost for the enterprise customers, so their migration towards high speed Ethernets will be facilitated by this explosion of Ethernet in all different parts of the network,” he contends.||**||

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