Types of Computer Networks

Networks can be categorized in several different ways. One method defines the type of a network according to the geographic area it spans. Alternatively, networks can also be classified based on topology or on the types of protocols they support.

• Client-Server Networks

Client and Server Hardware

Client/server networking grew in popularity many years ago as personal computers (PCs) became the common alternative to older mainframe computers.

Client devices are typically PCs with network software applications installed that request and receive information over the network. Mobile devices, as well as desktop computers, can both function as clients.

A server device typically stores files and databases including more complex applications like Web sites. Server devices often feature higher-powered central processors, more memory, and larger disk drives than clients.

Client-Server Applications

The client-server model organizes network traffic by a client application and also by a device. Network clients send messages to a server to make requests of it. Servers respond to their clients by acting on each request and returning results. One server supports many clients, and multiple servers can be networked together in a server pool to handle increased processing loads as the number of clients grows.

A client computer and a server computer are usually two separate units of hardware each customized for their designed purpose.

For example, a Web client works best with a large screen display, while a Web server does not need any display at all and can be located anywhere in the world. In some cases, however, a given device can function both as a client and a server for the same application. Additionally, a device that is a server for one application can simultaneously act as a client to other servers, for different applications.

Some of the most popular applications on the Internet follow the client-server model including email, FTP and Web services. Each of these clients features a user interface (either graphic or text-based) and a client application that allows the user to connect to servers. In the case of email and FTP, users enter a computer name (or sometimes an IP address) into the interface to set up connections to the server.

Local Client-Server Networks

Many home networks utilize client-server systems on a small scale. Broadband routers, for example, contain DHCP servers that provide IP addresses to the home computers (DHCP clients). Other types of network servers found in the home include print servers and backup servers.

Client-Server vs. Peer-to-Peer and Other Models

The client-server model of networking was originally developed to share access to database applications among larger numbers of users. Compared to the mainframe model, client-server networking gives better flexibility as connections can be made on-demand as needed rather than being fixed. The client-server model also supports modular applications that can make the job of creating software easier. In so-called two tier and three tier types of client-server systems, software applications are separated into modular components, and each component is installed on clients or servers specialized for that subsystem.

Client-server is just one approach to managing network applications. The primary alternative to client-server, peer-to-peer networking, treats all devices as having equivalent capability rather than specialized client or server roles. Compared to client-server, peer to peer networks offer some advantages such as better flexibility in expanding the network to handle a large number of clients. Client-server networks generally offer advantages over peer-to-peer as well, such as the ability to manage applications and data in one centralized location.

• Peer-to-Peer Networks

Peer-to-peer networking is an approach to computer networking in which all computers share equivalent responsibility for processing data. Peer-to-peer networking (also known simply as peer networking) differs from client-server networking, where certain devices have responsibility for providing or “serving” data and other devices consume or otherwise act as “clients” of those servers.

Characteristics of a Peer Network

Peer-to-peer networking is common on small local area networks (LANs), particularly home networks.

Both wired and wireless home networks can be configured as peer-to-peer environments.

Computers in a peer-to-peer network run the same networking protocols and software. Peer networks devices are often situated physically near one another, typically in homes, small businesses and schools. Some peer networks, however, utilize the internet and are geographically dispersed worldwide.

Home networks that use broadband routers are hybrid peer-to-peer and client-server environments. The router provides centralized internet connection sharing, but files, printer, and other resource sharing are managed directly between the local computers involved.

Peer-to-Peer and P2P Networks

Internet-based peer-to-peer networks became popular in the 1990s due to the development of P2P file-sharing networks such as Napster. Technically, many P2P networks are not pure peer networks but rather hybrid designs as they utilize central servers for some functions such as search.

Peer-to-Peer and Ad Hoc Wi-Fi Networks

Wi-Fi wireless networks support ad-hoc connections between devices. Ad hoc Wi-Fi networks are pure peer-to-peer compared to those that use wireless routers as an intermediate device. Devices that form ad hoc networks require no infrastructure to communicate.

Benefits of a Peer-to-Peer Network

P2P networks are robust.

If one attached device goes down, the network continues. Compare this with client-server networks when the server goes down and takes the entire network with it.

You can configure computers in peer-to-peer workgroups to allow sharing of files, printers and other resources across all the devices. Peer networks allow data to be shared easily in both directions, whether for downloads to your computer or uploads from your computer

On the internet, peer-to-peer networks handle a high volume of file-sharing traffic by distributing the load across many computers. Because they do not rely exclusively on central servers, P2P networks both scale better and are more resilient than client-server networks in case of failures or traffic bottlenecks.

Peer-to-peer networks are relatively easy to expand. As the number of devices in the network increases, the power of the P2P network increases, as each additional computer is available for processing data.

Security Concerns

Like client-server networks, peer-to-peer networks are vulnerable to security attacks.

Because each device participates in routing traffic through the network, hackers can easily launch denial of service attacks.

P2P software acts as server and client, which makes peer-to-peer networks more vulnerable to remote attacks than client-server networks.

Data that is corrupt can be shared on P2P networks by modifying files that are already on the network to introduce malicious code.

• Introduction to Area Networks

One way to categorize the different types of computer network designs is by their scope or scale. For historical reasons, the networking industry refers to nearly every type of design as some kind of area network. Common types of area networks are:

LAN – Local Area Network

WAN – Wide Area Network

WLAN – Wireless Local Area Network

MAN – Metropolitan Area Network

SAN – Storage Area Network, System Area Network, Server Area Network, or sometimes Small Area Network

CAN – Campus Area Network, Controller Area Network, or sometimes Cluster Area Network

PAN – Personal Area Network

LAN and WAN are the two primary and best-known categories of area networks, while the others have emerged with technology advances

Note that network types differ from network topologies (such as bus, ring and star).

LAN: Local Area Network

A LAN connects network devices over a relatively short distance. A networked office building, school, or home usually contains a single LAN, though sometimes one building will contain a few small LANs (perhaps one per room), and occasionally a LAN will span a group of nearby buildings. In TCP/IP networking, a LAN is often but not always implemented as a single IP subnet.

In addition to operating in a limited space, LANs are also typically owned, controlled, and managed by a single person or organization.

They also tend to use certain connectivity technologies, primarily Ethernet and Token Ring.

WAN: Wide Area Network

As the term implies, a WAN spans a large physical distance. The Internet is the largest WAN, spanning the Earth.

A WAN is a geographically-dispersed collection of LANs. A network device called a router connects LANs to a WAN.

In IP networking, the router maintains both a LAN address and a WAN address.

A WAN differs from a LAN in several important ways. Most WANs (like the Internet) are not owned by any one organization but rather exist under collective or distributed ownership and management. WANs tend to use technology like ATM, Frame Relay and X.25 for connectivity over the longer distances.

LAN, WAN and Home Networking

Residences typically employ one LAN and connect to the Internet WAN via an Internet Service Provider (ISP) using a broadband modem. The ISP provides a WAN IP address to the modem, and all of the computers on the home network use LAN (so-called private) IP addresses. All computers on the home LAN can communicate directly with each other but must go through a central network gateway, typically a broadband router, to reach the ISP.

Other Types of Area Networks

While LAN and WAN are by far the most popular network types mentioned, you may also commonly see references to these others:

Wireless Local Area Network – A LAN based on Wi-Fi wireless network technology

Metropolitan Area Network – A network spanning a physical area larger than a LAN but smaller than a WAN, such as a city. A MAN is typically owned and operated by a single entity such as a government body or large corporation.

Campus Area Network – A network spanning multiple LANs but smaller than a MAN, such as on a university or local business campus.

Storage Area Network – Connects servers to data storage devices through a technology like Fibre Channel.

System Area Network (also known as Cluster Area Network) – Links high-performance computers with high-speed connections in a cluster configuration.