Bandwidth, bandwidth, bandwidth. As the telecommunications industry experiences unexpected exponential growth in data traffic, the demand for this commodity has become insatiable. Not only has there been an increase in the number of telecommunications subscribers, but also a tremendous increase in the online time used by existing subscribers, as well as a demand for greater speeds for attached devices and their applications. Over 50% of all traffic consists of data, rather than voice and video signals, a percentage that will continue to increase dramatically over the coming years as streaming video and voice-over IP (VoIP) signals emerge.
What's the answer to this dilemma? Telecommunications vendors say that the solution is to expand or retrofit existing networks and build new networks. A key element in this plan is the move to optical networking, which inherently carries much greater bandwidth capacity than the existing infrastructure.
Almost everyone in the networking industry sees the primary goal as scaling the optical backbone infrastructure by a factor of a thousand over the coming years. Will that produce a bandwidth glut? It doesn't appear likely. But with technological innovations occurring at a rapid pace, it's possible that bandwidth could ultimately become a tradable commodity, claims John Ryan of RHS, an optical-networking market-research firm. Instead of selling a fiber-optic cable or a wavelength on a cable, carriers and network service providers will simply sell bandwidth.
Before all of this can happen, though, cost considerations must be carefully addressed. The deregulation of the telecommunications industry in 1996 increased competition among the existing carriers and stimulated the establishment of many new independent carriers. Investments in network expansions have brought in higher revenues, but significantly increased operational costs and lower prices have placed a strain on profitability.
Other problems include the long provisioning time involved in establishing a connection for a customer and the need for improved quality of service (QoS), the measure of a carrier's ability to meet the customer's needs. QoS refers to the availability of the network with the needed bandwidth and the assurance of reliability, low error and jitter rates, and security.
As mentioned earlier, the two basic strategies for increasing the available bandwidth while controlling costs are to expand or retrofit existing networks and to build new networks. Both strategies are widely implemented on Synchronous optical networks, or Sonet (see "A Sonet Primer," p. 90).
Expanding and retrofitting existing Sonet backbone systems can be performed by three fundamental methods: by lighting up dark (unused) fibers, increasing transmission speeds in existing fibers, or by adding dense wavelength-division multiplexing (DWDM). The third approach is a way of multiplexing multiple data systems on a single fiber by employing laser transmitters on different frequencies. In most networks, unused or dark fibers can be called into service by adding additional equipment.
Higher speeds also are possible by installing new equipment. Data rates of 155 Mbits/s (OC-3) and 622 Mbits/s (OC-12) are still the most common today. Even the oldest of fiber-optic cables, though, is capable of handling data rates up to approximately 10 Gbits/s. Currently, there's a rapid in-crease in the adoption of OC-48 equipment (2.5 Gbits/s) with a trend toward 10 Gbits/s (OC-192). It will take a few more years to get to the OC-768 level of 40 Gbits/s or beyond, but we will surely arrive there.
The same basic strategies apply when building new networks, where communications providers are implementing DWDM and pushing for the highest speeds possible per fiber and per wavelength. Additionally, newer, greatly improved fiber-optic cables provided by suppliers, such as Corning, Lucent Technologies, Pirelli (now Cisco), and others, are easing the bandwidth crutch.
These newer fiber cables have lower losses and dispersion distortion than older fiber cables. This means higher speeds can be achieved over longer distances. The lower loss enables longer cable runs to be achieved before signal regeneration is required. Signal regeneration is typically necessary every 40 km or so. This optical/electrical/optical (OEO) conversion is expensive. New systems need fewer regenerations and, in many cases, none at all.
Another approach is to implement more optical and fewer electronic components. The development of erbium-doped fiber amplifiers (EDFAs) and Raman amplifiers has already begun to minimize the OEO expense and increase a fiber's span distance without regeneration. The use of optical switches eliminates OEO conversion too, and it offers the benefit of being speed and protocol independent. Also, by automating the switches, provisioning and network reconfiguration can occur faster and at lower cost.
In addition to the above solutions, three other trends are emerging. First, there's significant growth in metropolitan-area networks (MANs). While the long-distance backbone networks are undergoing expansion and upgrading, an astonishing number of MANs are being constructed in major cities to provide companies better accessibility to the high-speed backbone.
Plus, many expect the ubiquitous ring topology of Sonet to gradually be replaced with a packet-carrying mesh network that's more efficient and provides alternate paths for the signal. While that trend will no doubt develop in the future, the installed legacy Sonet networks can easily carry packet data associated with ATM, Ethernet, or other formats.
Each year, many more analysts predict the ultimate demise of Sonet. But with such a massive investment in these networks, they're not likely to be quickly replaced. Aside from that, the sales of new Sonet networks are actually increasing. Optical networks will obviously evolve, but newer non-Sonet architectures will show up first in MANs.
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