Sunday, March 9, 2008

Assingment 5

Network topology

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.
A local area network (LAN) is one example of a network that exhibits both a physical topology and a logical 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. Likewise, the mapping of the flow of data between the nodes in the network determines the logical topology of the network. It is important to note that the physical and logical topologies might be identical in any particular network but they also may be different.
Any particular network topology is determined only by the graphical mapping of the configuration of physical and/or logical connections between nodes. LAN Network Topology is, therefore, technically a part of graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies may be identical.

Primary difference between Bridge and Gateway

(1) A node on a network that serves as an entrance to another network. In enterprises, the gateway is the computer that routes the traffic from a workstation to the outside network that is serving the Web pages. In homes, the gateway is the ISP that connects the user to the internet.
In enterprises, the gateway node often acts as a proxy server and a firewall. The gateway is also associated with both a router, which use headers and forwarding tables to determine where packets are sent, and a switch, which provides the actual path for the packet in and out of the gateway.
(2) A computer system located on earth that switches data signals and voice signals between satellites and terrestrial networks.
(3) An earlier term for router, though now obsolete in this sense as router is commonly used.

Network bridge
A bridge for interconnecting data networks includes an adapter connected to each network and a central programmed processor. Each adapter includes a receive and a transmit FIFO storage which is less than the packets being transferred from one network to the other.
The control program generates Receive Buffer Descriptors which include buffer pointers, buffer length fields and pointers to next descriptors. These Descriptors are used by the adapters to buffer received packets which are directed to another network. When a packet is buffered the control program generates Transmission Descriptors which are used by the adapter to transfer packet data to the other network.
The control program modifies packet when needed by by generating and storing in its memory only the modified portion and including in the Receive Buffer Descriptor pointers which the buffered information which is to be transmitted and the sequence.


This is a form of LAN architecture is which nodes on a network are connected to a common central hub or switch, and this is done by the use of dedicated links. The Star topology is now emerging as the most common network layout used today in LAN layout. Each workstation is connected point-to-point to a single central location.


In the bus topology the server is at one end, and the client PCs (devices) are connected at different points or positions along the network. All signals pass through each of the devices. Each device has a unique identity and can recognize those signals intended for it. It is easy and simple to design and implement.

The Mesh topology is a variation of the bus, in which all devices are connected to one another in a daisy-chain fashion, as opposed to connecting in sequence to a single network cable. Each node is capable of transmitting, receiving, and routing data.

LAN Ring Topology

This topology is a simple design and consists of a single cable that forms the main data path in the shape of a ring. Each device is connected to a closed loop of cable. Signals travel in one direction from one node to all other nodes around the loop.

LAN Tree Topology

The Tree topology is essentially a hybrid of the bus and star layouts. The basic topology is similar to that of a bus, with nodes connected in sequence to a linear central cable. But tree networks may have "branches" that contain multiple workstations that are connected point-to-point in a star-like pattern. Signals from a transmitting node travel the length of the medium and are received by all other nodes.

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