Networking is a complex part of computing that makes up most of the IT Industry. Without networks, almost all communication in the world would cease to happen. It is because of networking that telephones, televisions, the internet, etc. work.

One way to categorize computer networks is by their geographic scope, although many real-world networks interconnect Local Area Networks (LAN) via Wide Area Networks (WAN)and wireless networks[WWAN]. These three (broad) types are:

[edit] Local area network (LAN)

A local area network is a network that spans a relatively small space and provides services to a small number of people.

A peer-to-peer or client-server method of networking may be used. A peer-to-peer network is where each client shares their resources with other workstations in the network. Examples of peer-to-peer networks are: Small office networks where resource use is minimal and a home network. A client-server network is where every client is connected to the server and each other. Client-server networks use servers in different capacities. These can be classified into two types:

1. Single-service servers

2. print server,

where the server performs one task such as file server, ; while other servers can not only perform in the capacity of file servers and print servers, but they also conduct calculations and use these to provide information to clients (Web/Intranet Server). Computers are linked via Ethernet Cable, can be joined either directly (one computer to another), or via a network hub that allows multiple connections.

[edit] Wide area network (WAN)

A wide area network is a network where a wide variety of resources are deployed across a large domestic area or internationally. An example of this is a multinational business that uses a WAN to interconnect their offices in different countries. The largest and best example of a WAN is the Internet, which is a network composed of many smaller networks. The Internet is considered the largest network in the world.^[7]. The PSTN (Public Switched Telephone Network) also is an extremely large network that is converging to use Internet technologies, although not necessarily through the public Internet.

A Wide Area Network involves communication through the use of a wide range of different technologies. These technologies include Point-to-Point WANs such as Point-to-Point Protocol (PPP) and High-Level Data Link Control (HDLC), Frame Relay, ATM (Asynchronous Transfer Mode) and Sonet (Synchronous Optical Network). The difference between the WAN technologies is based on the switching capabilities they perform and the speed at which sending and receiving bits of information (data) occur.

[edit] Metropolitan Area Network (MAN)

A metropolitan network is a network that is too large for even the largest of LAN’s but is not on the scale of a WAN. It also integrates two or more LAN networks over a specific geographical area ( usually a city ) so as to increase the network and the flow of communications. The LAN’s in question would usually be connected via “backbone” lines.

For more information on WANs, see Frame Relay, ATM and Sonet.

[edit] Wireless networks (WLAN, WWAN)

A wireless network is basically the same as a LAN or a WAN but there are no wires between hosts and servers. The data is transferred over sets of radio transceivers. These types of networks are beneficial when it is too costly or inconvenient to run the necessary cables. For more information, see Wireless LAN and Wireless wide area network. The media access protocols for LANs come from the IEEE.

The most common IEEE 802.11 WLANs cover, depending on antennas, ranges from hundreds of meters to a few kilometers. For larger areas, either communications satellites of various types, cellular radio, or wireless local loop (IEEE 802.16) all have advantages and disadvantages. Depending on the type of mobility needed, the relevant standards may come from the IETF or the ITU.

[edit] Network topology

The network topology defines the way in which computers, printers, and other devices are connected, physically and logically. A network topology describes the layout of the wire and devices as well as the paths used by data transmissions.

Network topology has two types:

• Physical
• logical

Commonly used topologies include:

Bus

Star

• Tree (hierarchical)
• Linear
• Ring
• Mesh
  • partially connected
  • fully connected (sometimes known as fully redundant)

The network topologies mentioned above are only a general representation of the kinds of topologies used in computer network and are considered basic topologies.

The OSI layers may be summarised by:

1. Physical layer: Provides electrical, functional, and procedural characteristics to activate, maintain, and deactivate physical links that transparently send the bit stream; only recognises individual bits, not characters or multicharacter frames.
2. Data link layer: Provides functional and procedural means to transfer data between network entities and (possibly) correct transmission errors; provides for activation, maintenance, and deactivation of data link connections, grouping of bits into characters and message frames, character and frame synchronisation, error control, media access control, and flow control (examples include HDLC and Ethernet)
3. Network layer: Provides independence from data transfer technology and relaying and routing considerations; masks peculiarities of data transfer medium from higher layers and provides switching and routing functions to establish, maintain, and terminate network layer connections and transfer data between users.
4. Transport layer: Provides transparent transfer of data between systems, relieving upper layers from concern with providing reliable and cost effective data transfer; provides end-to-end control and information interchange with quality of service needed by the application program; first true end-to-end layer.
5. Session layer: Provides mechanisms for organising and structuring dialogues between application processes; mechanisms allow for two-way simultaneous or two-way alternate operation, establishment of major and minor synchronisation points, and techniques for structuring data exchanges.
6. Presentation layer: Provides independence to application processes from differences in data representation, that is, in syntax; syntax selection and conversion provided by allowing the user to select a “presentation context” with conversion between alternative contexts.
7. Application layer: Concerned with the requirements of application. All application processes use the service elements provided by the application layer. The elements include library routines which perform interprocess communication, provide common procedures for constructing application protocols and for accessing the services provided by servers which reside on the network.

The communications engineer is concerned mainly with the protocols operating at the bottom four layers (physical, data link, network, and transport) in the OSI reference model. These layers provide the basic communications service. The layers above are primarily the concern of computer scientists who wish to build distributed applications programs using the services provided by the network.

“Hop-by-Hop” “Network-wide” and “End-to-End” Communication

The two lowest layers operate between adjacent systems connected via the physical link and are said to work “hop by hop“. The protocol control information is removed after each “hop” across a link (i.e. by each System) and a suitable new header added each time the information is sent on a subsequent hop.

The network layer (layer 3) operates “network-wide” and is present in all systems and responsible for overall co-ordination of all systems along the communications path.

The layers above layer 3 operate “end to end” and are only used in the End Systems (ES) which are communicating. The Layer 4 – 7 protocol control information is therefore unchanged by the IS in the network and is delivered to the corresponding ES in its original form. Layers 4-7 (if present) in Intermediate Systems (IS) play no part in the end-to-end communication.