Raising the Bandwidth Ceiling

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As organizations have come to depend on LANs and WANs, they've put more applications and information on their networks. Speedy retrieval of such information becomes critical to such organizations. This retrieval is where the need for additional bandwidth most often manifests itself.

Conventional text-only documents don't normally put much strain on a network. But today, data often takes the form of audio, video, graphics, and other types of multimedia. Such files of data streams are much larger than plain-text files and often impose delivery deadlines on networks. If this is hard to picture, think how frustrating it is when the audio track and the video track get out of synch on your TV, and then multiply this frustration by several orders of magnitude. Then, think about what delivering time-sensitive audio, video, or multimedia data across a network really requires.

Such complex forms of data can easily consume the full bandwidth of an ordinary 10-Mbps network while handling only one or two users' needs. That's why an increasing appetite for higher-bandwidth networks is emerging in the workplace. Such added bandwidth is increasingly necessary to handle the more complex types of data traversing the network and to prepare the infrastructure to deal with emerging applications, such as network teleconferencing, network telephony, collaborative development, and all kinds of other gee-whiz technologies now under construction.

This is why we feel compelled to tell you about some of the cabling alternatives available for today's networks that might be able to handle tomorrow's bandwidth needs. Please read the sidebars in this chapter for the full picture if you really want to understand what's out there!

100-Mbps Ethernet

Two flavors of 100-Mbps Ethernet are available today, each with its own particular access method: CSMA/CD (this means Carrier Sense Multiple Access with Collision Detection; we discuss it in detail in Chapter 4) and demand priority (as described later in this chapter). When proposals for 100 Mbps were solicited, two factions emerged: one that used the same CSMA/CD access method used in conventional Ethernet (now known as Fast Ethernet or 100BaseT), and another that used a demand priority access method (now known as 100BaseVG-AnyLAN).

Both factions put proposals forward to implement their approaches. Curiously, both proposals were ultimately accepted as standards, but each one fell under different IEEE committees . Today, the Fast Ethernet standard falls under the 802.3 standards family, and the 100BaseVG-AnyLAN standard falls under the IEEE 802.12 standards family.

100BaseT is similar to 10BaseT except that it runs 10 times faster. When implementing 100BaseT, you need to use equipment designed for 100BaseT throughout your network, but otherwise , designing and building the network is pretty much the same as for 10BaseT. It's even possible to mix and match 10BaseT and 100BaseT technologies on a single network, but you need to include hubs that have 10-Mbps and 100-Mbps capabilities to bring these two worlds together.

100BaseVG-AnyLAN offers the same bandwidth as 100BaseT but uses four pairs of wires instead of two pairs in each cable. Doubling the number of pairs enables a different access method, called demand priority , to control access to the network medium. In addition, 100BaseVG-AnyLAN permits devices on the network to receive and transmit at the same time (that's one reason why the number of pairs in the cable is doubled ).

100BaseVG-AnyLAN hubs help manage the demand priority scheme and provide arbitration services when multiple requests for network access occur at more or less the same time. When using the CSMA/CD access method, workstations listen before sending, and they transmit as soon as they recognize that the medium is not in use. This arrangement leads to collisions when two or more stations begin to broadcast at more or less the same time, especially as network utilization increases . When a demand priority device wants to transmit data across the network, it signals the hub, and the hub determines when that device may access the network. This setup eliminates collisions and allows networks to function at higher utilization rates than CSMA/CD can support.

On the downside, networking equipment and cabling for 100BaseVG-AnyLAN is more expensive than that for 100BaseT, even though 100BaseVG-AnyLAN offers better performance. Perhaps that's why 100BaseT has proven more popular in the marketplace than 100BaseVG-AnyLAN has.

Gigabit Ethernet

You're probably wondering what you can implement on your network when you start running out of bandwidth even with 100-Mbps technology. From there, the next step up is to Gigabit Ethernet. Although Gigabit Ethernet technologies are currently available, they're not yet in broad use. However, because the need for speed will never decrease, we want to give you a taste of this technology so you can salivate over it even if it's unlikely to show up in your office any time soon.

To begin with, Gigabit Ethernet is not typically used as a networking solution for the desktop. (In fact, no conventional PC or other desktop machine can come close to saturating a Gigabit Ethernet network.) Rather, Gigabit Ethernet is used primarily as a backbone technology, especially in large networks where certain pathways need to carry huge amounts of traffic. Ideally, Gigabit Ethernet helps boost server-to-server communications and permits ultra -fast data transfers between switches on a network backbone.

Gigabit Ethernet uses the CSMA/CD access method and the same frame size and formats as conventional Ethernet. Therefore, you can integrate this technology into existing Ethernet networks easily, and you don't need to buy new protocol analyzers, network management software, and so forth.

To jump on the Gigabit Ethernet bandwagon, the devices you need to add to your network include

  • Suitable NICs and connectors for your servers

  • Proper cables (fiber- optic , in most cases, though twisted-pair options are under development)

  • Upgrades to the routers and switches that handle Gigabit Ethernet traffic

In some cases, this emerging standard may require you to replace certain pieces of equipment; but modern routers and switches need only new EPROM chips and upgrades for certain interface cards. Eventually, as the price of the technology drops , you may even consider adding Gigabit Ethernet interfaces into your high-end workstations. This probably won't be necessary for a few more years , however.

Tip 

The Gigabit Ethernet Alliance offers a terrific white paper on this technology. You can download it at http://www.10gea.org/ (look in their Technology section for the 10GEA white paper). It gives a great overview of Gigabit Ethernet and describes what types of applications demand this kind of network speed.

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Windows Server 2003 for Dummies
Windows Server 2003 for Dummies
ISBN: 0764516337
EAN: 2147483647
Year: 2003
Pages: 195

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