More Than One Network Is an Internetwork

Another subtlety of networking has to do with the relationship between individual cable segments and the network that encompasses all of them. For historical reasons too tedious to relate, the term network is often used to describe only those devices that attach to a single cable segment.

The many flavors of WAN links

WAN links run the gamut of functionality, bandwidth, and associated costs, and include a broad range of technologies. These days, Windows Server 2003 does a good job of supporting all types of WAN links because of its multiprotocol and router support, including:

• Intergrated Services Digital Network (ISDN): This relatively low-speed digital link connects through the telephone system, giving it nearly global reach. Windows Server 2003 includes built-in drivers for a variety of ISDN interfaces and supports a broad range of ISDN-based bandwidths. Normal ISDN connections occur through a so-called basic rate interface (BRI) and support one or two 64 Kbps data channels for a maximum bandwidth of 128 Kbps. Monthly costs for a typical ISDN connection vary from a low of $100 a month to as high as $500 a month in some markets. Some ISDN rates accumulate on a per minute basis, so be sure to check with your local telecom company.

• General Digital Subscriber Line (xDSL): This term describes a higher-bandwidth technology that also uses conventional phone lines to handle digital data. (There are many types of DSL lines; therefore, the x stands for general.) Windows Server 2003 includes drivers for a range of xDSL devices. Most conventional xDSL devices offer bandwidths that range from 256 Kbps to as high as 1.544 Mbps. xDSL costs are still unclear in many markets, but it looks like xDSL will ultimately replace ISDN.

• Cable modems: Cable modems use CATV coaxial cables to send and receive network data. Although cable modems are not available in all markets, most metropolitan areas serviced by national cable TV companies, such as Time Warner or Cox Communications, now offer cable modem connections. Cable modems usually offer high bandwidth downstream (up to 1.544 Mbps for incoming data) but less bandwidth upstream (up to 512 Kbps for outgoing data). Cable modems are way cheap and can cost as little as $40 a month (but the medium is shared, unlike all the other alternatives mentioned here, so more users means less individual bandwidth).

• Satellite links: Several of the satellite television providers have begun to offer highspeed satellite access to the Internet. In most cases, the download speed is only 2 to 10 times faster than the upload speed, but if you can't get an ISP or telecom connection to your network, it's a way to go. Most satellite uplinks range from about $50 a month to nearly $500.

• T1/E1 or T3/E3: These terms name the most common high-end digital services for medium- sized companies and larger. T1/T3 describes two classes of digital service available in North America; E1/E3 describes two similar classes of service available in Europe and elsewhere. Bandwidth for T1 is 1.544 Mbps; for T3 it's 45 Mbps; for E1 it's 2.048 Mbps; and for E3 it's 34.368 Mbps. All these services cost at least $500 a month and use expensive equipment. T3/E3 costs $20,000 a month or more in most markets.

• Asynchronous Transfer Mode (ATM): This describes an extremely high-bandwidth technology. It's the WAN technology of choice for phone and other communications companies, and comes in a variety of implementations that range from 155 Mbps to 2.48 Gbps. Windows Server 2003 includes support for various ATM implementations .

 

This limited interpretation of the word network made it necessary to invent the term internetwork . An internetwork is what happens when some devices (such as repeaters, bridges, routers, and gateways) are attached to two or more cable segments to create a network of networks. In internetworks, information from one cable segment can flow through one or more of those devices to move from one cable segment to another. The mother of all internetworks is the worldwide Internet itself, which is a network of more networks than you (or we) wnat to think about for too long.

Warning 

When you're dealing with technical talk about networks, be sure that you understand what the word network means in the context of whatever discussion is underway. In most cases, it doesn't matter that what may commonly be referred to as a network is really an internetwork, but when it does matter, it matters a lot. So pay attention!