EXPERIMENT NO 2

Network Components

The various components used in networking are :- 1. Repeaters 2. Hubs3. Bridges 4. Switch 5. Router 6. Gateway

Repeaters• Every network architecture has a maximum cable length beyond which signals cannot

be transmitted.• Repeaters are used to reconstruct signal and thus extend the reach of a network.• When the signal is reconstructed, they are able to reach the maximum length of the

cable, thus reducing the interference of electrical signal.• Repeaters operate in the physical layers of the OSI model.• These are analog devices that are connected to two cable segments.• Repeaters do not understand packets, frames, or headers. They understand volts.• Repeaters works in co-axial environment.

HubsThey are multiport repeaters and also work on physical layer.

Bridges• These are devices used to join two or more network segments acting like a repeater

with an added advantage of monitoring address of data packets. In this way, it filters data packets that don’t need to be sent. This causes a delay in transfer rate, as each address of the packets has to be monitored.

• In data link layers we find bridges.

• When frames arrive, software in the bridge extracts the destination address from the header and looks it up in the table to see where to send the frame. For Ethernet this address is the 48bit destination address. Like a hub, a modern bridge has line cards, usually for four or eight inputs lines of certain types. A line card for Ethernet cannot handle token ring frames. But, a bridge may have line card for different network types and different speeds.

• With a bridge each line is its own collision domain, in contrast to Hub.

Switches• It is similar to bridge in that both route on frame address. It is mostly used to connect

individual computers. If A wants to send a frame to host B, the switch actively forward the frame from A to B, but bridge cannot. Each switch port goes to single computer; switch must have space for many more line cards. Each line card provides buffer space for frames arriving on its port since each port is it’s own collision domain, switch never lose frames to collisions. However, if frames come in faster than they can be retransmitted, the switch may run out of buffer space and have to discard frames.

• To eliminate this problem slightly, modern switches start forwarding frames as soon as the destination header field has come in. these switches don’t use store-and –forward switching. This is called cut through switches (CUTS). It is handled entirely in hardware, but bridge use CPU that did store-and–switching in software. But all the modern bridges and switches contain special integrated cut for switching; there is almost no technical difference.

Routers• Router is like intelligent bridge that can be programmed for passing or not passing

either data of a particular nature or to a particular user.• Router use information within packets to determine the best route through a network

of LANs• Router supports multiple alternate paths between locations and can select best path

based on traffic loads, line speeds and cost.• Some routers are capable of linking dissimilar networks, such as an Ethernet segment

to a token ring network.• It operates in the network layer.• When packets come in to a router, the frame header mad trailer area stripped off and

the packet located in the frame’s payload field is passed to the routing software. This software uses the packet header to choose an output line. The routing software does not see the frame address and does not even know whether the packet came in LAN or a point-to-point line.

Gateways• Gateways connects between different networks (for example, PC networks in offices

connected to an ISPs network)• Gateways operate from the transport layer to the application layer of the OSI model.