Computer Network

Subrata Paul Roll : 13015411 DEPT. of CSE University of Rajshahi

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Context: What is switch ? Working of switch. Characteristics of switch. Some manufacturer of networking switch What is Hub. Characteristics of Hub. Working of Hub. Comparison of switch and hub

What is switch ?A network switch is a computer networking device that is used to connect multiple computer together within on local area network(LAN). In other words, it is capable to determine specific source and destination.

Technically, network switch operate at layer two (Data link layer) of the OSI model. The network switch commonly refers to routes data at the data link layer of the OSI model.

Working of Switch Switch is an interconnecting device with 16 or 24 ports in common. All other devices are connected to these ports . Whenever any machine sends packet to any other machine, source machine send packet to switch, switch then forwards it to destination machine. Each packet which comes to switch contains source and destination physical address in it, on basis of which switch forwards packet to other machine. Switch always sent packet based on destination MAC address. Its process is as follows: (process also known as Switching)

Working of Switch (continue..)

When switch receives a packet from any device, it checks for its destination MAC address.

Then switch compares destination MAC address with its MAC Address Table for corresponding MAC address.

o If MAC Address is found, packet is sent out to port against which MAC Address was matched.

If entry is not found, Unknown  unicasts (when the switch  doesn't have a port mapping for a destination  mac address in the frame)  are treated like broadcasts by Layer Two  devices, and are flooded out  of all ports except the port on which the  frame originated.

Working of Switch (continue..)

Now question comes, how does switch knows on which port destination machine is connected?

For this switch uses one table in its cache memory called MAC Address table or Forwarding Table in which switch stores that at which port which machine is connected by storing its physical address (MAC Address). So table contains two columns (Physical Address and Port Number) and rows equal to number of ports in switch.  When switch is turned ON, by default there is no entry in MAC address table, as communication starts, based on devices involved entries are created in table

Characteristics of switch Uses MAC address for data transfer. Filter data before forwarding it to its destination of on

the network. Connect LAN segments. Multiple collision domain but single broadcast domain. Layer 2 (data link) device. Data transfer to specific port. Transmission mode are full duplex. No collision occur in in full duplex. Data transmission form are frame.

Different type of switch

Some manufacturer name of switch

D-Link Billion Electronic ECI Telecom Cisco Systems Juniper network Oracle corporation

What is hub ?Hub is the most basic networking device that connects multiple computers or other network devices together. a network hub has no routing tables or intelligence on where to send information and broadcasts all network data across each connection.

Characteristics of Hub Hub propagate signals through the network. It cannot determine the best path. It cannot filter network traffic. Layer 1(physical layer) device. Centralize device. Connect multiple Ethernet device together.

Working of HubWhen a packet arrive at one port from a source it is copied to the other ports so that all segments of LAN can see all packet and hub forward the segments to all connected devices then accept this segment only expected destination other device discard this segment.

Working of Hub(continue…)

Working of Hub(continue…)

This simulation illustrates the basic operation of a hub.Computer 1 sends a ping message to Computer 3. when the ping reaches the hub, it doesn’t see the actual data In the message. It only sees bit signals, cleans them up and Sends them out all connected ports.

When Computer 2 and 4 receive the bits signals they reassemble them into frame, check the destination addressAnd discard the frame because it is not addressed to them.Computer 3 receives the frame successfully and sends aReply..

Working of Hub(continue…)

Once the reply sends the hub, the hub again forwards the bit Signals out all connected ports, Computer 2 & 4 discard the Fram.e Computer 1 successfully receive the ping reply

Comparison of switch and hubSuppose, we have four computer, four computer are connected to a hub, now two computer of them communicate with each other, hub simply pass the message through all network traffic to each of four Computer, where a computer receive this message.

On the other hand, switches are capable of determiningthe destination of each individual traffic element and selectively forwarding data to the one computer that actually need it.