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Micro House PC Hardware Library Volume II: Network Interface Cards And Modems Micro House PC Hardware Library Volume II: Network Interface Cards And Modems
by Micro House International, Inc. and Scott Mueller
Que, Macmillan Computer Publishing
ISBN: 078971664x   Pub Date: 06/17/98
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Using ATM

Asynchronous Transfer Mode is one of the newest of the high-speed technologies. It has been in an “emerging” state for some time now, without having developed into its full potential. ATM defines a Physical layer protocol in which a standard size 53-byte packet (called a cell) can be used to transmit voice, data and real-time video over the same cable, simultaneously. The cells contain identification information that allow high-speed ATM switches (wiring hubs) to separate the data types and ensure that the cells are reassembled in the right order.

The basic ATM standard runs at 155Mbps, but some implementations can go as high as 660Mbps. Work is also progressing on an ATM desktop standard that runs at 25Mbps, but this doesn’t seem to be enough of a gain over Token Ring’s 16Mbps to be worth the adoption of an entirely new networking technology.

ATM is a radically different concept, and there are no convenient upgrade paths as there with the 100Mbps standards described earlier. All the networking hardware must be replaced, and the ATM products currently on the market are still riding the wave of extremely high prices that are common to any new technology. For this reason, ATM is being used primarily for WAN links at this time. When the delivery of real-time video over the network becomes more of a practical reality than it is now, ATM might find its rightful place. For now, it remains a niche technology with very good potential.

TCP/IP and the Internet

TCP/IP stands for Transmission Control Protocol/Internet Protocol. It is the colloquial name given to the suite of networking protocols used by the Internet, as well as by most UNIX operating systems. TCP is primarily the Transport layer protocol in the suite, and IP defines the Network layer protocol that transmits blocks of data to the host.

TCP/IP is an extensive collection of Internet protocol applications and transport protocols, and includes File Transfer Protocol (FTP), Terminal Emulation (Telnet), and the Simple Mail Transfer Protocol (SMTP). TCP/IP was originally developed by the U.S. Department of Defense in the 1970s as platform and hardware-independent medium for communication over what was to become known as the Internet. A good example of this independence is the capability of DOS, Windows, or Windows 95 workstations to access information and transfer files on the Internet, which is a mixed platform environment. The primary advantages of TCP/IP are:

  Platform Independence. TCP/IP is not designed for use in any single hardware or software environment. It can and has been used on networks of all types.
  Absolute Addressing. TCP/IP provides a means of uniquely identifying every machine on the Internet.
  Open Standards. The TCP/IP specifications are publicly available to users and developers alike. Suggestions for changes to the standard can be submitted by anyone.
  Application Protocols. TCP/IP allows dissimilar environments to communicate. High-level protocols like FTP and Telnet have become ubiquitous in TCP/IP environments on all platforms.

Although it has been the protocol of choice on UNIX networks for many years, the explosive growth of the Internet has brought the protocols onto all kinds of LANs as well. Many network administrators are finding that they can adapt their current NOSes to use TCP/IP, and thus lessen the network traffic problems that can be caused by running several different sets of protocols on the same network.

Connecting to the Internet

You can connect a computer to the Internet through virtually any of the access ports discussed in this chapter thus far. Individual computers can use modems to connect to an Internet Service Provider (ISP), or a network connection can be established through which all of the users on the LAN gain access. Depending on your organization’s degree of Internet involvement, any one of the following access options can be selected.

Asynchronous Modem Connections

Individual computers can use normal asynchronous modems attached to a serial port to connect to the Internet, through the services of an ISP. ISPs provide dial-in capabilities using either the PPP (Point-to-Point Protocol) or the SLIP (Serial Line Internet Protocol). Both of these protocols are part of the TCP/IP suite, and are now provided by virtually all of the third-party TCP/IP stacks available for DOS and Windows 3.1. Windows 95 and Windows NT include support for both protocols as part of the operating system. Whichever protocol you use must be supported by the TCP/IP stack on the remote computer, as well as the system to which you are connecting. Your service provider will be able to tell you what protocols are supported by the host system.

SLIP
The SLIP is an extremely simple protocol that provides a mechanism for the packets generated by IP (called datagrams) to be transmitted over a serial connection. It sends each datagram sequentially, separating them with a single byte known as the SLIP END character to signify the end of a packet. SLIP provides no means of error correction or data compression, and was eventually superseded by the PPP.
PPP
The PPP improves the reliability of serial TCP/IP communications with a three-layer protocol that provides the means for implementing the error correction and compression that SLIP lacks. Most TCP/IP stacks provide PPP support, as do most of the ISPs operating today. When given a choice, you should always select PPP over SLIP; it provides superior throughput and reliability.

ISDN Connections

An increasingly popular option for Internet connectivity is the ISDN connection. Providing speeds of 128Kbps (when both B channels are combined), it is more than four times faster than a 28.8Kbps modem connection. ISDN can be used to provide Internet access to a network or to an individual computer. The basics of ISDN communications are covered in the “Integrated Services Digital Network” section earlier in this chapter.

For basic e-mail connectivity and modest use, an ISDN connection could support 10 to 20 users on a network nicely. Giving users a taste of the Internet often leads to a substantial habit, however, and you may find that World Wide Web browsing and FTP transfers cause you to quickly outgrow an ISDN link.


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