BT aims for first European live dwdm network
By EDWARD HARROFF
In the newly deregulated European markets, telecommunications carriers are viewing dense wavelength-division multiplexing (dwdm) technology as a competitive advantage. A bold example of this is in Europe`s most competitive long-distance communications market--the United Kingdom. British Telecom (BT) is running two pilot long-distance network links using 16-channel dwdm systems, moving the company another step closer to a high-capacity all- optical transport network for that country.
The two new links--one of 200 km between Belfast, Northern Ireland, and Carlisle, UK, and another from Newcastle, UK, to Edinburgh, Scotland (see figure on page 26)--will be able to move network traffic at speeds to 40 Gbits/sec (to 2.44 Gbits/channel). This is 16 times faster than is possible on existing long-distance optical-fiber systems in Europe.
Ewart Lowe, of BT Laboratories` Optical Design and Planning Group (Martlesham Heath, UK) says, "Eleven suppliers responded to BT`s invitation-to-tender for these dense wdm launch projects, and four were short-listed. wdm suppliers had to offer more than just a 16-channel wdm system to meet BT`s strict requirements. The four principal components needed to win BT`s approval were 16-channel wdm features, multistandard transponder interface support (more than just Synchronous Digital Hierarchy), optical protection switching, and remotely managed network management systems."
These launch systems, which will operate on two of the longest and busiest routes in the United Kingdom, are expected to enter service this year. The technology will be installed on both direct and backup routes between the locations, working with two key suppliers: Ericsson on the Edinburgh-to-Newcastle route and Lucent Technologies on the Belfast-to-Carlisle route. BT is aiming to make these links the first in Europe to carry live traffic via dwdm.
Jim Jackson, BT`s core transmission strategy manager, says, "This technology will enable BT to develop its optical network to cope with increasing bandwidth demands as well as further improve its efficiency and resilience. Because these networks can use existing fibers, dwdm represents an extremely speedy and cost-effective way of increasing network capacity."
The two new routes will include two radical new features--optical protection switching and a transparent transponder interface--not currently implemented in terrestrial wdm systems deployed elsewhere in the world, according to BT.
Optical protection switching can automatically restore the entire link in the event of a complete failure (such as a cable break) so that the problem is imperceptible to customers, and services are not affected. This is achieved by optically switching all 16 wavelengths to an alternative route in less than 50 msec (one-twentieth of a second). This is important for this type of wdm system, which has the potential to carry up to half a million voice calls, and particularly in the case of the Belfast-Carlisle submarine link, which is exposed to the risks of damage by trawlers in the Irish Sea.
The second unique feature, the transparent transponder interface to the wdm system, will allow BT`s large existing optical network to be loaded and protected on the wdm system, along with new Synchronous Digital Hierarchy systems being deployed for network growth. According to Jose Maria Daza of Ericsson, "The erion family of systems work with all existing transport network equipment, not just fibers, by simply plugging in the optical outputs from an existing network system, atm [Asynchronous Transfer Mode] switches, or other network components." This removes the need for fiber building on long routes, while enhancing the resilience of BT`s existing optical-fiber network and providing an excellent platform for atm and Internet protocols (e.g., fast IP interconnect).
Lowe sums up his group`s objectives by explaining, "This deployment shows BT carrying the torch in optical network development and, with commercial network products now becoming available, the many years of research work on wdm at BT Laboratories is coming to fruition. These first wdm systems will form the building blocks for a national optical transport network which will carry BT into the twenty-first century." q
Edward Harroff writes from Bellevue, Switzerland.