In the computer world, the term describes two or more connected computers that can share resources such as data, a printer, an Internet connection, applications, or a combination of these. We’ll discuss each type of network and describe the situation that is most appropriate for its use.
Local Area Network
By definition, a local area network (LAN) is limited to a specific area, usually an office, and cannot extend beyond the boundaries of a single building. The first LANs were limited to a range (from a central point to the most distant computer) of 185 meters (about 600 feet) and no more than 30 computers. Today’s technology allows a larger LAN, but practical administration limitations require dividing it into small, logical areas called workgroups.
A workgroup is a collection of individuals (a sales department, for example) who share the same files and databases over the LAN.
Wide Area Network
A WAN is any network that crosses metropolitan, regional, or national boundaries. Most networking professionals define a WAN as any network that uses routers and public network links. The Internet fits both definitions.
WANs differ from LANs in the following ways:
The Internet is actually a specific type of WAN. The Internet is a collection of networks that are interconnected and, therefore, is technically an internetwork(Internet is short for the word internetwork).
A WAN can be centralized or distributed. A centralized WAN consists of a central computer (at a central site) to which other computers and dumb terminals connect. The Internet, on the other hand, consists of many interconnected computers in many locations. Thus, it is a distributed WAN.
Host, Workstation, and Server
Networks are made up of lots of different components, but the three most common network entities are the host, workstation, and server. Each one of these items can be found on most networks.
The term host covers pretty much every other networking device, but it can also refer to a work station and server and is most commonly used when discussing TCP/IP-related services and functions. In fact, a host, in TCP/IP terms, is any network device that has an IP address. Work stations, servers, and any other network device (as long as it has one or more IP addresses) can all be considered hosts. In conversation, you may also hear the word host used to describe any minicomputer or server.
The term host comes from the era when the only intelligent devices on the network were mainframes, which were commonly referred to as hosts regardless of TCP/IP functionality. Nearly all other devices were known as dumb terminals, but no other device had intelligence only the mainframe. As TCP/IP came into the picture, only the mainframes, or hosts, received IP addresses. This is the same era that produced the term gateway to refer to any layer 3 intermediate device, such as a router. Just as the term gateway remains in common use today, such as in the very common term default gateway, the term host is still used, but its use is much broader now that nearly every end and intermediate device is intelligent and has at least one IP address, making them hosts.
In the classic sense, a workstation is a powerful computer used for drafting or other math-intensive applications. The term is also applied to a computer that has multiple central processing units (CPUs) available to users. In the network environment, normally the term refers to any computer that is connected to the network and used by an individual to do work.
It is important to distinguish between workstations and clients. A client is any network entity that can request resources from the network; a workstation is a computer that can request resources. Workstations can be clients, but not all clients are workstations. For example, a printer can request resources from the network, but it is a client, not a workstation.
In the truest sense, a server does exactly what the name implies: It provides resources to the clients on the network (“serves” them, in other words). Servers are typically powerful computers that run the software that controls and maintains the network. This software is known as the network operating system.
Servers are often specialized for a single purpose. This is not to say that a single server can’t do many jobs, but, more often than not, you’ll get better performance if you dedicate a server to a single task. Here are some examples of servers that are dedicated to a single task:
File Server: Holds and distributes files.
Print Server: Controls and manages one or more printers for the network.
Proxy Server Performs a function on behalf of other computers. (Proxy means “on behalf of.”)
Application Server Hosts a network application.
Web Server Holds and delivers web pages and other web content using the Hypertext Transfer Protocol (HTTP)
Mail Server Hosts and delivers e-mail. It’s the electronic equivalent of a post office.
Fax Server Sends and receives faxes (via a special fax board) for the entire network without the need for paper.
Remote Access Server Listens for inbound requests to connect to the network from the outside. Remote access servers provide remote users (working at home or on the road) with a connection to the network, either via modems or an IP connection.
Telephony Server Functions as a “smart” answering machine for the network. It can also per form call center and call-routing functions.
Peer-to-Peer vs. Client/Server Architecture
The purpose of networking is to share resources. How this is accomplished depends on the architecture of the network operating system software. The two most common network types are peer-to-peer and client/server.
If you were to look at an illustration of a group of computers in a LAN, it would be impossible to determine if the network was a peer-to-peer or a client/server environment. Even a videotape of this same LAN during a typical workday would reveal few clues as to whether it is peer-to-peer or client/server. Yet, the differences are huge. Since you can’t see the differences, you might guess correctly that they are not physical but logical.
In peer-to-peer networks, the connected computers have no centralized authority. From an authority viewpoint, all of these computers are equal. In other words, they are peers. If a user of one computer wants access to a resource on another computer, the security check for access rights is the responsibility of the computer holding the resource.
Each computer in a peer-to-peer network can be both a client that requests resources and a server that provides resources. This is a great arrangement, provided the following conditions are met:
Networks that run Windows 95/98 as their network operating system and networks using Windows NT, 2000, or XP in a workgroup are considered peer-to-peer networks. Peer-to-peer networks present some challenges. For example, backing up company data becomes an iffy proposition. Also, it can be difficult to remember where you stored a file. Finally, because security is not centralized, users and passwords must be maintained separately on each machine.
In contrast to a peer-to-peer network, a client/server network uses a network operating system designed to manage the entire network from a centralized point, which is the server. Clients make requests of the server, and the server responds with the information or access to a resource.
Physical vs. Logical Concepts
Generally speaking, when we’re referring to the physical aspects of a network, we’re referring to some aspect of the network that you can touch or that has physical substance (like electrons, electrical pulses, or the way cables are run). That is, they exist in the physical world. Logical concepts, on the other hand, are more imaginary and esoteric and deal with things like how data flows in a network. So, when we’re describing something as either physical or logical in nature, you’ll understand how those terms apply.
Client/server networks have some definite advantages over peer-to-peer networks. For one thing, the network is much more organized. It is easier to find files and resources because they are stored on the server. Also, client/server networks generally have much tighter security. All usernames and passwords are stored in the same database (on the server), and individual users can’t use the server as a workstation. Finally, client/server networks have better performance and can scale almost infinitely. It is not uncommon to see client/server networks with tens of thousands of workstations. Note that the server now holds the database of user accounts, passwords, and access rights.
Note that today’s networks are very often hybrids of the peer-to-peer model and the client/ server model. Clients of early Novell NetWare networks, for example, had no ability to share their resources, not that they had many worth sharing, for the most part. Conversely, today’s Microsoft and Apple networks, for example, have well-defined servers. They also allow the simultaneous sharing of resources from lesser devices that run what are considered workstation operating systems, which are capable of fewer inbound connections but are running the server service nonetheless. Purists shun the less organized mixture of this resource sharing among servers and clients alike, but the reality is that most networks would be worse off for losing this capability.
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