Summary of LAN hardware for the network design:

LAN network

LAN hardware

Description

Problem

To connect two computers

NIC

Network interface card for connecting two computers on LAN

Cannot connect over long distances

To connect two computers over long distances

Repeater

Extends the distance limitations of Ethernet cable by boosting the signal

Only two computers can be connected if you want to connect more computers then it is a problem

To connect more than two computers

Hub

hub is a multiport device for building star-configured topologies with twisted-pair cable

It cannot filter traffic

It is confined to small network

maximum nodes can be 30

To connect more than two computers in small network which can filter traffic.

Bridge

Provides repeater functions along with selective filtering of traffic to reduce congestion and contention

Bridges have limited ports

It introduce latency for large networks.

For large network .

Switches

Basically a multiport bridge that segments a network into many smaller collision domains while maintaining the broadcast characteristics. Greatly improves the performance of LANs

Here network traffic travels to all LAN segments without knowing the exact IP address of the destination segment.

It controls collision domains but not broadcast domains.

For internetworks ( connecting more than one LAN network with high speed and flexibility)

Router

Routers make forwarding decisions based on network layer addresses.

In addition to controlling collision domains, routers control broadcast domains

.

Switching:

Circuit-switching networks

In this technique, first the complete physical connection between two computers is established and then data are transmitted from the source computer to the destination computer

Dedicated paths are used between source and destination.

no queuing

Example: telephone systems.

Message Switching

In this technique, the source computer sends data or the message to the switching office first, which stores the data in its buffer. It then looks for a free link to another switching office and then sends the data to this office. This process is continued until the data are delivered to the destination computers. Owing to its working principle, it is also known as store and forward. That is, store first (in switching office), forward later, one jump at a time.

The network receives the entire messages, stores them in a

Secondary storage and transmit them.

It provides long term storage even after the message has

been delivered.

Example:

Hop-by-hop Telex forwarding and UUCP are examples of message switching systems.

E-mail is another example of a message switching system

Packet Switching

. In packet switching no fixed path is created between devices that communicate; it is broken into packets, each of which may take a separate path from sender to recipient.

The message is divided into a number of slices called

Packets of certain fixed size.

Each packet has its destination address.

Queuing involved

Routing is needed

errors involved

Example: when you connect to the Internet using a dial-up modem.

Network topologies:

In Computer Networking topology refers to the layout or design of the connected devices.

Topology can be classified into two :

1-D (bus)

2-D (tree, stars, rings, mesh, etc.)

13.8.1 Point to Point Topology

Point to Point topologies are simplest and most straightforward. Point-to-point (PTP) topology connects two nodes directly together You can think of as a chain of devices and another name for this type of connectivity is called daisy chaining. Most computers can 'daisy chain' a series of serial devices from one of its serial ports. Networks of routers are often configured as point-to-point topologies.

The following examples are pure point to point links:

Two computers communicating via modems.

A mainframe terminal communicating with a front end processor.

A workstation communicating along a parallel cable to a printer.

Advantage:

It is easy to set up

Installation Cost is low

Fault identification is easy

Allows flexibility in communication hardware, packet formats, etc.

Provides security and privacy because communication channel is not shared

Disadvantages

Number of wires grows as square of number of computers

Connections between buildings can be prohibitive

Adding a new computer requires N - 1 new connections

13.8.2Linear Bus

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.

Access and control of bus networks are typically maintained by a method called

contention, whereby if a line is unused, a terminal or device can transmit its message at will, but if two or more terminals initiate messages simultaneously, they must stop and transmit again at different intervals

Fig. 1. Linear Bus topology

Advantages of a Linear Bus Topology

The advantage of the Bus network is that if one computer fails in the network the others are still not affected and they continue to work.

Bus network is very simple and easy to set up. If there is an urgent need to set up a network and perhaps be used on a short term basis then the Bus network is the best possibility.

Bus networks use the least amount of cable to set up making it cost effective.

Disadvantages of a Linear Bus Topology

Entire network shuts down if there is a break in the main cable.

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.

13.8.3Star Topology

A star topology consists of a central connection hub to which devices are connected with UTP (Unshielded Twisted Pair) Ethernet. Contrary to the bus topology, a star topology utilizes a point-to-point connection to connect each node to the central hub. The hub acts as a signal booster as well, and all the data traffic that transverses the network passes through this hub.The entire network is dependent upon the central hub in a star topology, so if the entire network is not working, it means that there is problem in the hub. This makes it easy to troubleshoot the network because of the only one point for error correction. As all the computers in star topology are independent to each other and dependent only on the central hub, network failure or other network problems are less likely to happen. The privacy of each of the computers is also maintained in this topology.In star topology, new devices and nodes can be easily added and by just extending a cable from the hub.

Advantages of star topology:

A star topology is simple in functionality and easy to manage.

If a problem occurs in the network, it can be easily isolated and cleared.

It is very easy to expand the star topology because of its simple format.

Disadvantages of star topology:

The entire network of the star topology is completely dependent on the hub. If the hub fails, the whole network fails.

Network connection may slow down when the number of nodes increases or the cable lengthens.

Star topology needs more cable length than other topologies.

It is more expensive compared to bus topology.

Star Topology

13.8.4Ring Topology

A ring topology consists of network of computers in which each node connects to exactly two other nodes. This forms a single continuous path for the flow of signals through each nodes of the network. Data travels from node to node, with each node along the way handling every packet. Each of the nodes in the ring topology are connected to each other through only one pathway, so the failure of only one link disrupts the whole network.To overcome this fallacy, the data in a ring topology is transmitted both clockwise and counter clockwise, so that if there is single break of the cable, all the nodes on both sides can be reached.

Ring Topology

Advantages of Ring Topology

It is an orderly network in which all the nodes in the network have equal access to all the resources.

Its performance is far better compared to star topology under heavy network.

It does not need network servers to manage the connections.

Disadvantages of Ring Topology

If one of the workstations fails to operate, it may lead to the unusability of the whole network.

Addition and removal of devices in the network can affect the entire network.

Ring network is slower than the Ethernet network.

13.8.5Tree topology

A tree topology consists of bus and star topologies framed in a common network. The tree like structure of this network allows the colleges, schools, universities and other institutions to maintain their own network as a branch of a bigger network through which they can maximize their area of access to the network. This type of network topology is most suitable for such networks which are widely spread and divided into many branches.On tree topology the hubs of each smaller topologies are connected to the central hub that c