Networks

Networks

internet: a network that connects networks - the Internet is the largest of the internets

The Internet is a type of network. Specifically, it is a network that connects networks. In other words, it is an internet. The Internet is capitalized to differentiate it from smaller internets that connect smaller groups of networks. Those internets, of course, may also connect to the Internet.

LAN: a Local Area Network is a network that connects a localized group of computers

There are many types of networks out there. The basic network is the local area network. A local area network, or LAN, is a network that connects a localized group of computers. This can be as small as a single group of computers in a single room or as large as an entire company or college campus. Larger LANs are usually comprised of a collection of smaller internetworked LANs.

WAN: a Wide Area Network is a network that connects networks over some distance

The next primary grouping for networks is the wide area network, or WAN. WANs are networks that connect LANs over large distances. The Internet is the biggest example of a wide area network. Another type of WAN is the Metropolitan Area Network (MAN), which serves the internetworking needs of a large metropolitan area. While LANs are usually managed by the entities that own and use the computers attached to them, and WANs are managed by dedicated network transmission companies, MANs are usually managed by local telephone companies, using their wiring for their data lines.

intranet: usually used to refers to Web a site internal to a company and meant for employees only

Intranets & Extranets

Two other general network terms worth knowing are intranets and extranets. An intranet is LAN network that serves many of the same functions of the Internet internal to a company. Usually it refers specifically to Web pages that are internal to a company and only accessible to employees. An extranet is a similar concept except that it is a network that connects companies or entities that are working together and need to share information. The term intranet (within the net) was coined as a variation on internet (between nets). The term extranet (outside the net) was then derived from intranet.

It should be noted that Web pages for intranets are easier to write, since you know that everyone is, or at least should be, using the same Internet software.

Hardware

medium: a means of conveying something

The Internet, and networks in general, are comprised of various devices that handle the physical operation of the network. The first of these is the transmission media, or the means of transmitting the signal between computers. What qualifies as a transmissions medium is pretty much wide open. If we wanted we could send information with smoke signals, but it wouldn't be very efficient and would require lots of human intervention. Typical transmission media for information technology can include any of the following, running from local to global:

client-server: a hierarchical network arrangement where workstations (clients) are linked to function specific computers (servers) that provide various services

• physical cables
  • copper wire
  • twisted pair
  • coaxial
  • fiber optic
• infra-red
• radio
• microwave
• satellite relay

Locally networks tend to function in some sort of client-server relationship. A client is a computer that someone is using to access the network. A server is a computer that performs some function for the network, such as storing files, or managing the printers, or connecting to the Internet. There can be multiple servers on a network, each with specialized or overlapping tasks. In peer-to-peer networks it is possible for computers to function as both clients and servers, since server functions are distributed around the network.

gateway: a computer that functions as an intermediary between a local network and a wide-area network

Gateways and Routers

A computer responsible for connecting networks together is called a gateway computer. Sometimes they are also called proxy servers. A proxy server is a gateway that hides information about the local network, such as addresses, before sending information out onto an internet. On the Internet, gateways function as peers, which means they are all equally responsible for making sure the message gets through. There is no central machine coordinating the process. Rather, the process is distributed amongst all participating computers.

proxy server: a server that stands in for another server, usually a gateway which masks information about the LAN to which it connects

Another type of computer that helps the Internet to work properly is a router. A router is responsible for passing along packets of information until they get to their destination. A gateway can be seen as a specialized router that routes between local and remote networks, while other routers route primarily between other remote networks.

peer: a computer that functions as an equal with other machines on the network

Routers perform two primary tasks. One is to receive packets, evaluate their addresses, and pass them along toward their destination. The other is to keep track of which paths are open. The Internet is a complex, heavily interconnected network. Unlike simple local area networks which are usually linear in nature (or in a unidirectional data ring, which is just a straight line running in a circle), the Internet is literally interconnected like a spider's web, with computers where the web strands connect. This means that there are usually many ways to get to a given destination.

router: a computer that determines where packets of data are supposed to be sent and routes them on their way

Routers attempt to send packets along the best path, best being a combination of fastest and shortest. To help them do so, they have to keep track of which paths are working. The process by which they do so is simple. First, if the router finds a path that appears to not be working, which they determine by whether they get a response to signals sent down it, they remove it from the list of working paths and ignore it until told otherwise. Second, routers talk to one another, and on a regular basis update each other on currently active paths. The entire Internet, just by routers and gateways passing updates to other routers thay are directly connected to, can entirely update all address databases for the entire Web in under 48-hours without any action on the part of anyone but the automated systems.

These pages can be found at: [http://academ.hvcc.edu/~kantopet/]
Copyright 2003 -- Peter L. Kantor[kantopet@hvcc.edu]
Last Updated August 2003