Week 6:

Network topology is the layout pattern of interconnections of the various elements (links, nodes, etc.) of a computer^[ or biological network. Network topologies may be physical or logical.Physical topology refers to the physical design of a network including the devices, location and cable installation. Logical topology refers to how data is actually transferred in a network as opposed to its physical design. In general physical topology relates to a core network whereas logical topology relates to basic network.

There are basic categories two of network topologies;

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 Logical topology :

                the mapping of the flow of data between the nodes in the network determines the logical topology of the network etermines the physical topology of the network.

The study of network topology recognizes eight basic topologies:^[

Point-to-point;

The simplest topology is a permanent link between two endpoints. Switched point-to-point topologies are the basic model of conventional telephony. The value of a permanent point-to-point network is unimpeded communications between the two endpoints. The value of an on-demand point-to-point connection is proportional to the number of potential pairs of subscribers, and has been expressed as Metcalfe's Law.

Bus network topology ;

Topologi "linear bus" terdiri daripada suatu kabel utama dengan suatu penamat (terminator) dikedua-dua hujungnya. Semua nod (seperti komputer pelayan, stesyen kerja dan peranti lain) disambung kepada kabel linear ini. Contoh rangkaian yang menggunakan topologi Linear Bus ini ialah Ethernet dan LocalTalk.

Star network topology ;

In local area networks with a star topology, each network host is connected to a central hub with a point-to-point connection. The network does not necessarily have to resemble a star to be classified as a star network, but all of the nodes on the network must be connected to one central device. All traffic that traverses the network passes through the central hub. The hub acts as a signal repeater. The star topology is considered the easiest topology to design and implement. An advantage of the star topology is the simplicity of adding additional nodes. The primary disadvantage of the star topology is that the hub represents a single point of failure.

Advantages

v  Easy to install, and wire.

v  Easy to add new workstations

v  No disruptions to the network when connecting or removing devices.

v  Any non-centralised failure will have very little effect on the network

v  Easy to detect faults and to remove parts.

v  Centralized control

v  Centralized network/hub monitoring

Disadvantages

v  Requires more cable length than a linear topology.

v  If the hub or concentrator fails, nodes attached are disabled.

More expensive than linear bus topologies because of the cost of the concentrators

Ring network topology;

A network topology that is set up in a circular fashion in which data travels around the ring in one direction and each device on the right acts as a repeater to keep the signal strong as it travels. Each device incorporates a receiver for the incoming signal and a transmitter to send the data on to the next device in the ring. The network is dependent on the ability of the signal to travel around the ring.

Fully connected mesh topology;

Partially connected mesh topology;

The type of network topology in which some of the nodes of the network are connected to more than one other node in the network with a point-to-point link – this makes it possible to take advantage of some of the redundancy that is provided by a physical fully connected mesh topology without the expense and complexity required for a connection between every node in the network.

Tree network topology

Advantage

v  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.

Hybrid;

Hybrid networks use a combination of any two or more topologies in such a way that the resulting network does not exhibit one of the standard topologies (e.g., bus, star, ring, etc.). For example, a tree network connected to a tree network is still a tree network topology. A hybrid topology is always produced when two different basic network topologies are connected. Two common examples for Hybrid network are: star ring network and star bus network.

Daisy chain;

Except for star-based networks, the easiest way to add more computers into a network is by daisy-chaining, or connecting each computer in series to the next. If a message is intended for a computer partway down the line, each system bounces it along in sequence until it reaches the destination. A daisy-chained network can take two basic forms: linear and ring.