how are networks categorized??

its usually classified using three properties:

• topology
• protocol
• architecture

Network Topology 

• network topology is also called network structures
• indicates how a network is design or lay out
• has both a logical level & physical level
• The physical topology of a network is determined by the capabilities of the network access devices and media, the level of control or fault tolerance desired, and the cost associated with cabling or telecommunications circuits.
• The logical topology, in contrast, is the way that the signals act on the network media, or the way that the data passes through the network from one device to the next without regard to the physical interconnection of the devices
• has 4 main type :

1. bus
2. star ring
3. hybrid

                                          

     

Bus topology
A linear bus topology consists of a main run of cable with a terminator at each end. All nodes (file server, workstations, and peripherals) are connected to the linear cable.Ethernet and LocalTalk networks use a linear bus topology.The bus cable carries the transmitted message along the cable. As the message arrives at each workstation, the workstation computer checks the destination address contained in the message to see if it matches it's own. If the address does not match, the workstation does nothing more. If the workstation address matches that contained in the message, the workstation processes the message. The message is transmitted along the cable and is visible to all computers connected to that cable.

 Advantages of a Linear Bus Topology

• Easy to connect a computer or peripheral to a linear bus. 
• Requires less cable length than a star topology.

Disadvantages

• Entire network shuts down if there is a break in the main cable. 
• A faulty cable or workstation will take the entire LAN down 
• terminators are required at both ends of the backbone cable. 
• Difficult to identify the problem if the entire network shuts down. 
• Not meant to be used as a stand-alone solution in a large building. 

Star topology 
A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub or concentrator. Data on a star network passes through the hub or concentrator before continuing to its destination. The hub or concentrator manages and controls all functions of the network. It also acts as a repeater for the data flow.This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable.The protocols used with star configurations are usually Ethernet or LocalTalk.

Advantages

• Easy to install, and wire. 
• Easy to add new workstations 
• No disruptions to the network when connecting or removing devices. 
• Any non-centralised failure will have very little effect on the network 
• Easy to detect faults and to remove parts. 
• Centralized control Centralized network/hub monitoring

Disadvantages

• Requires more cable length than a linear topology. 
• If the hub or concentrator fails, nodes attached are disabled. 
• More expensive than linear bus topologies because of the cost of the concentrators.

3.Star-Wired
A star-wired topology may appear (externally) to be the same as a star topology. Internally, the MAU (multistation access unit) of a star-wired ring contains wiring that allows information to pass from one device to another in a circle or ring. The Token Ring protocol uses a star-wired topology.

4. tree topology 
A tree topology combines characteristics of linear bus and star topologies.It consists of groups of star-configured workstations connected to a linear bus backbone cable. Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.

Network Interface Controller

network interface controller - (NIC or "network interface card") An adapter circuit board installed in a computer to provide a physical connection to a network.

Network Operating System

An operating system that is designed for network use. Normally, it is a complete operating system with file, task and job management; however, with some earlier products, it was a separate component that ran under the OS; for example, LAN Server required OS/2, and LANtastic required DOS.

Unix, Linux, NetWare, Windows 2000 Server and Windows Server 2003 are examples of network operating systems designed for use in stand-alone servers. Such products may also include a Web server, directory services, messaging system, network management and multiprotocol routing capabilities.

Multiuser File Sharing
A network operating system (NOS) manages concurrent requests from clients and provides the security necessary in a multiuser environment. A file sharing component is installed in each client machine that interacts with the server to share files and applications as well as network devices such as printers, faxes and modems.

Peer-to-Peer Operating Systems
In a peer-to-peer network, such as Windows 98, XP, Vista or Win7, where each client machine can also be a server, the OS might still be considered a network operating system, but it is more lightweight than a full-blown NOS.

Network Switch

A network switch or switching hub is a computer networking device that connects network devices. The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer of the OSI model. Switches that additionally process data at the network layer and above are often referred to as layer-3 switches or multilayer switches.

Repeater

(1) A communications device that amplifies (analog) or regenerates (digital) the data signal in order to extend the transmission distance. Available for both electronic and optical signals, repeaters are used extensively in long distance transmission. They are also used to tie two LANs of the same type together. Repeaters work at layer 1 of the OSI model.

(2) The term may also refer to a multiport repeater, which is a hub in a 10Base-T network.

Local Talk

LocalTalk refers to the physical networking -- that means the built-in controller in many Apple computers, the cables and the expansion cards required on some systems. The "official" Apple cabling system typically uses a "bus topology" where each device in the network is directly connected to the next device in a daisy chain. The illustration on the Farallon book cover below gives an idea of how a bus looks.

Token Ring

A local area network (LAN) access method developed by IBM. Conforming to the IEEE 802.5 standard, Token Ring uses a token ring access method and connects up to 255 nodes in a star topology at 4, 16 or 100 Mbps. All stations connect to a central wiring hub called the "Multistation Access Unit" (MAU) using twisted wire cable.

Different than Ethernet
The Token Ring MAU may be a central hub, but does not function like a shared Ethernet hub. The Token Ring method is more deterministic and ensures that all users get regular turns at transmitting their data. With Ethernet, all users compete to get onto the network.

Type 1 and Type 3
Type 1 Token Ring networks allow up to 255 stations per network and use shielded twisted pair wires with IBM style Type 1 connectors. Type 3 Token Rings allow up to 72 devices per network and use unshielded twisted pair (Category 3, 4 or 5) with RJ-45 connectors.