New fiber links for Australian trunk network

Oct. 1, 1997

New fiber links for Australian trunk network

By PAUL MORTENSEN

Optus Communications, Sydney, Australia, has inaugurated an OC-192 (10-Gbit/sec), 2300-km fiber ring between Sydney and Melbourne. The system, which can handle 129,000 simultaneous telephone calls, has four times greater capacity than other systems installed in Australia to date.

Presently, Australia has two competing optical broadband trunk networks that have been installed between its major cities by Telstra (Melbourne) and Optus. It also has two competing broadband access networks (now under construction), which are driven mainly by local call competition.

Optus has set up the new Sydney-to-Melbourne link in a "diverse path," with sets of fibers running along different routes between the two cities. This arrangement provides automatic protection for the traffic on the ring and ensures service even in the event of an accidental fiber cable cut or an equipment failure. One path runs along the Pacific coast, and the other is inland.

The system is based on the flash-192 multiplexer from Fujitsu Network Communications. Although the flash-192 system is a Synchronous Optical Network (Sonet) product based on the North American standard, it is being used effectively in a nation whose fiber-optic networks are based on the prevailing international standard, Synchronous Digital Hierarchy (sdh). In effect, the flash-192 multiplexers communicate with each other using a Sonet protocol, but carry an sdh payload.

According to Fujitsu, the key difference is the way the overhead is defined: by packaging an sdh payload into an OC-192 envelope, the overhead is still Sonet, and the way it communicates is Sonet. The content of the envelope is irrelevant to the transmission scheme; in this case, the envelope contains sdh stm-16, the equivalent of Sonet`s OC-48 (2.5-Gbit/sec) protocol. At the OC-192 rate, there is little to distinguish Sonet from sdh.

The Sydney-Melbourne project has four exchanges--two each in Sydney and Melbourne--plus 16 regenerator sites. All flash-192 regenerators are housed in controlled-environment vaults that house previous OC-48 (2.4-Gbit/sec) systems between these two cities.

Optical amplifiers enable distances between repeater stations of greater than 150 km (93 mi), compared with an average of 50-km spacing in most of Australia`s trunk networks. This reduces the number of elements needed to build the network.

Requirements fulfilled

Currently, Australia has three telecommunications carriers--Telstra, Optus, and Vodaphone--and a host of resellers. Telstra, the incumbent, provides international, trunk, and local fixed access. Optus provides international and trunk access (see figure). Meanwhile, both are rolling out duplicate hybrid fiber/coaxial-cable (hfc) networks that will pass more than 2.5 million homes in the next two years in what is dubbed the world`s fastest cable rollout. The hfc-based services will include telephony, cable TV, and Internet-like broadband services.

Optus is also planning to install a second 1000-km fiber link between Sydney and Brisbane. The existing cable between the two cities takes a coastal route and is buried just 1.2 m from the surface, which means there is a high risk of accidental cuts. The second cable will travel through central New South Wales and South Eastern Queensland. The majority will be placed underground; however because of hard bedrock in several sections, existing aboveground infrastructure, such as high-voltage power poles, will also be used in some cases. The link will have the same architecture as the Sydney-to-Melbourne link.

With these additions to the trunk network, Australia probably has sufficient fiber to accommodate traffic growth for at least five years. Nevertheless, because of the Australian government`s current policy to ensure digital access to rural areas, Telstra will embark on a significant fiber cable-laying program to further the reach of digital capacity to regional and rural areas.q

Paul Mortensen writes from Australia.

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