WEEK 6 (NETWORK TOPOLOGY)

NIC

     A network interface controller (also known as a network interface card, network adapter, LAN adapter and by similar terms) is a computer hardware component that connects a computer to a computer network.

Whereas network interface controllers were commonly implemented on expansion cards that plug into a computer bus, the low cost and ubiquity of the Ethernet standard means that most newer computers have a network interface built into the motherboard.

     The network controller implements the electronic circuitry required to communicate using a specific physical layer and data link layer standard such as Ethernet, Wi-Fi, or Token Ring. This provides a base for a full network protocol stack, allowing communication among small groups of computers on the same LAN and large-scale network communications through routable protocols, such as IP. 

Network TOPOLOGY is divide by 3 ::

(1) Network topology

      - is the study of the arrangement or mapping of the elements (links, nodes, etc.) of a network, especially the physical (real) and logical (virtual) interconnections between nodes.

(2) Physical topology

     - Any given node in the LAN will have one or more links to one or more other nodes in the network and the mapping of these links and nodes onto a graph results in a geometrical shape that determines the physical topology of the network.

(3) Logical topology

- is the mapping of the flow of data between the nodes.

There are several basic types of topology in networks:

(1) 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.

(2) 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.

Advantage

• Point-to-point wiring for individual segments.

Disadvantages

• Overall length of each segment is limited by the type of cabling used.
• if the backbone line breaks, the entire segment goes down.
• More difficult to configure and wire than other topologies.

(5) ETHERNET

      Ethernet is the most widely-installed local area network ( LAN) technology. Specified in a standard, IEEE 802.3, Ethernet was originally developed by Xerox from an earlier specification called Alohanet (for the Palo Alto Research Center Aloha network) and then developed further by Xerox, DEC, and Intel. An Ethernet LAN typically uses coaxial cable or special grades of twisted pair wires. Ethernet is also used in wireless

ethernet cables

(6) LOCALTALK

     

    LocalTalk is a particular implementation of the physical layer of the AppleTalk networking system from Apple Computer. LocalTalk specifies a system of shielded twisted pair cabling, plugged into self-terminating transceivers, running at a rate of 230.4 kbit/s.CSMA/CA was implemented as a random multiple access method.

LocalTalk cable adapter

connect directly to the Ethernet and LocalTalk