Telekom Malaysia prepares for a fiber future
At the Optical Fiber Communication (OFC `97) conference held recently in Dallas, researchers of the Multiwavelength Optical NETworking (monet) Consortium detailed a national-scale fiber-optic network made up of three all-optical test beds. These test beds are proving the future technical feasibility of high-capacity commercial and defense communications systems using wavelength-division multiplexing (WDM), crossconnect, and dispersion-compensated fiber-optic cable technologies.
operate at different clock rates. Multiplexing the different bearers requires adding bits to each stream to ensure that the combined streams have a rate matching the aggregate flow rate. This bit-padding occurs each time a lower-rate stream is multiplexed to a higher- rate stream.
Multistep demultiplexing
The real cost of this procedure is most evident when the individual communications channel is delivered to the customer. Pulling a single E1 stream from the aggregate flow requires multistep demultiplexing from the highest level down to E1. Since each level requires equipment, the entire process is costly.
TM plans to confront this problem by deploying 30 synchronous digital crossconnects (sdxcs) throughout the trunk network. The sdxcs will connect incoming optical fibers directly through the node without switching them. This allows the E1 channels to be easily added and removed from higher-rate bit streams without having to go through several layers of multiplexing and demultiplexing, thus reducing the investment in corresponding equipment. Each crossconnect has a huge capacity--128 stm-1 links, each rated at 155 Mbits/sec. Ahmad did not reveal the name of the company that will supply this equipment.
As currently envisioned, four sdxcs will be deployed in Malaysia`s rural island comprising the states of Sabah and Sarawak. Twenty-six will be deployed on Malaysia`s main peninsula, with five concentrated in and around Kuala Lumpur to serve the Multimedia Super Corridor (msc). The msc represents the Malaysian government`s willingness to provide state-of-the-art communications to the nation, and TM is the sole provider of telecommunications infrastructure in the corridor. The msc will include sdh fiber rings that connect TM`s major facilities, gateways, and Asynchronous Transfer Mode switches. The rings will have a fiber core of 144 and 192 pairs, a much higher density than what is currently installed in Malaysia.
Synchronizing the network
An integral part of migrating from pdh to sdh is the establishment of a main clock that imposes a single timing on the entire information flow in the network. TM is adopting a hierarchical system composed of a primary reference clock governing the network through "master slave clocks." The hierarchy of the slave clocks is governed by the binomial expansion of 2N, where N corresponds to the number of different transmission rates in the network. TM plans to synchronize its entire network through two primary reference clocks, each physically separated from the other. Although only one clock will govern the network, the two clocks will be linked to and synchronous with each other, ready to keep the system governed if the primary clock fails.
However, even sdh networks are not totally synchronous. Because Malaysia is composed of a main peninsula and an island, each geographic section is likely to have its own clock rate. Local clocks will also take over certain portions of the network when there are faults or during maintenance. One of the more sensitive aspects of an sdh network is that it has little tolerance for variation in the clock rates of the different network segments. If the variation is significant, the entire network can fail. Ahmad did not identify the variation that would cause a system failure in TM`s network.
However, one of the advantages of an sdh network is that it can be operated and monitored by devices controlled by computer software. Ahmad did not discuss the software aspects of the sdh network, nor did he delve into how or whether TM would use sdh`s performance monitoring capability to improve performance within the pdh segments until the migration is complete. The software issue is tricky in sdh because upgrades in network elements do not necessarily have an additive effect on network performance, meaning that the software changes do not have an easily predictable effect on network performance. Therefore, successful migration from pdh to sdh requires a number of field tests to empirically determine threshold levels and tolerances throughout the network. Ahmad gave no indication of TM`s reliance on field trials or how important they are to the validation of TM`s overall strategy.
Despite the imperfections, TM is committed to sdh and, in 1994, completely ceased purchasing pdh equipment. More than any other network in Southeast Asia, Malaysia`s trunk network looks and operates like true sdh.
TM is not ignoring the customer access network. The company has a fiber-in-the-loop program that is subdivided into three major categories: fiber-to-the-office, fiber-to-the-zone, and fiber-to-the-street-side-cabinet. Each program replaces the copper feeder and the crossconnect cabinet with fiber and a self-contained cabinet complete with a rectifier system and copper terminations. However, TM considers fiber-to-the-home and fiber-to-the-desk as too futuristic to deserve any serious planning currently. In the short run, the technical issues are not paramount.
The overall success of Malaysia`s move to a more fiber-intensive and sdh system is likely to be constrained by the country`s current financial problems. The nation`s currency underwent severe devaluation a few months ago. To the extent that high-quality fiber and sdh equipment have to be imported, TM`s expansion program has become much more expensive. q
Stephen N. Brown is president of mev Inc., Nashville, TN. He writes Lightwave`s monthly "Regulation & Policy" column.