2. UNDERSTANDING THE INTERNET
2.8. H ARDWARE AND S OFTWARE C OMPONENTS
Figure 4. Internet Service Provider (ISP) Network with a Dial-up Connection
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Ro ut er
E thernet
Mod em (s)
Central Computer
Term inal
LAN Connected PC - Workstation
Modem HUB Router
CSU/DSU
Hub
Terminal S erver
PC or Mac
DIAL-UP SITE (USER’S HOME) VT100 Needed to
support dial up service.
Phone Line
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6 5
4
7
1
3
2
8
Terminal Server
ISP NETWORK
SOURCE: Carl Grzybowsky, 1994.
WHOLESALER (REGIONAL ISP) INTERNET
(Permanet Host) (Permanet Host)
(Intermittent Host)
11 Phone Company’s Leased Line
2.8.1. Minimum Hardware Requirements
The following minimum computer hardware is necessary for the dial-up connection.
1 . PERSONAL COMPUTER
The computer consists of a monitor, Central Process Unit (CPU), keyboard and often a mouse. Most common personal computers connected to the Internet are IBM-
compatible and Macintosh, which can be connected in two ways: (1) Remote (dial-up), via a modem and phone line, or (2) direct, via a network interface card. A computer directly connected to the ISP network is a permanent host. A computer remotely connected to the ISP network is an intermittent host, as it's on only during dial-up. For example, the computers at a university’s computer lab are often permanent hosts, and an individual user connecting through a modem from his home is an intermittent host.
2 . MODEM
Modulator/demodulator: An electronic device for converting between serial data from a computer and an audio signal suitable for transmission over telephone lines. In one scheme the audio signal is composed of silence (no data) or one of two frequencies representing 0 and 1. Modems are devices that allow computers to make a call and send data by sound waves over standard voice grade telephone lines. A pair of modems is needed for computers to communicate. Modem speeds vary and the connection speed is determined by the slowest modem of the pair.
3 . PHONE LINE
Just like any other call made, long distance charges apply if the ISP is not in within the user’s local area.
2.8.2. Additional Hardware Equipment
As mentioned, if a user decides to connect his network (LAN) to the Internet or if he himself is an ISP, additional hardware is necessary. The following is a description of this additional hardware.
4 . TERMINAL SERVER
If the central site (ISP) wants to accommodate dial-up connections (PCs at the user’s home), a terminal (remote access) server is used. There is a great variety in remote access equipment, from dedicated boxes to others that integrate the function via a PC or router.
5 . ETHERNET
It is the protocol that allows computers within a LAN to function. The LAN cabling type defines the network. Older versions of Ethernet use coaxial cable that loops from one computer to another, while other Ethernet connections use twisted-pair cable (similar to phone wire and also known as 10 base T). Newer Ethernet connections use fiber.
6 . HU B
A hub is a switching device for networks that run a wire for each workstation and for networks that use a twisted-pair wiring system. Each device can be plugged and unplugged into the network without affecting other computers since they are independently connected to the hub.
7 . CENTRAL COMPUTER
A centralized storage and processing machine can run applications that serve other workstations in the ISP network or LAN. Traditional services include on-line catalog, circulation, and backup. Internet services managed by the central computer include:
terminal gateway access, Domain Name Service, Post Office, Usenet, Gopher, and WWW servers.
8 . TERMINALS
An electronic device for entering data into a computer or a communications system and displaying data received. These simple devices are dependent on the single server to which they are attached. They are not stand-alone computers, like PCs, as they use the central computer to function.
9 . ROUTER
The device that connects networks together and passes packets among them is called a router. Internet routers are commercial products, and many thousands of routers currently exist within the Internet. As the name indicates, routers deal with routing, addressing, management of telecommunications links, and other issues of operation. In particular, routers maintain routing tables, which direct packets to reach a specific network (Kleinrock, 1976). As a traffic cop, the router identifies network segments and routes data packets to their destinations.
10. CSU/DSU
Channel service unit/data service unit: The CSU/DSU takes data from the router and translates it into the format needed by the telephone company leased line to connect to the Internet and viceversa. That is, the Channel Service Unit (CSU) is used to terminate a T-1, DS-1 or DS-0 (1.54 Mbps, 64 Kbps, 56 Kbps) digital circuit. The Data Service Unit (DSU) terminates the data circuit and converts the customer’s data stream into a bi-polar format for transmission. Instead of using a row of multiplexors and analog modems, the CSU/DSU relays the data streams into a single digital connection.
11. LEASED LINE
A leased line is provided by the telephone company to connect the ISP network with the wholesale provider (regional ISP). A wholesale provider connects the ISP or LAN to the Internet.
2.8.3. Software Requirements
Depending on the user’s needs different applications are necessary. Typically, Internet multimedia-applications, such as Netscape, are enough for most users. By itself, a browser such as Netscape allows: E-mail, FTP, Gopher, Newsgroups, pictures, and simple text usage. So, buying and installing the application are the first steps. The software
requirements to run a LAN or an ISP network are different (more expensive) than those to connect through a dial-up connection.