A Network Interface Card (NIC) is a circuit board that plugs into both clients and servers and controls the exchange of data between them (A specific software
“driver” must be installed depending on the make of the NIC. A physical transmission medium, such as twisted pair or coaxial cable interconnects all network interface cards to network hubs or switches. Ethernet and Token Ring are common network interface cards. Today’s cards supports 10baseT and
100baseT with automatic recognition
.
HUB
When the need for interconnecting more then 2 devices together then a device known as hub comes to picture. Basically hub is a layer one device. i.e. it operates on the physical layer of the OSI model. It is designed to do broadcasting i.e when it gets any frame it broadcasts it to every port irrespective that whether it is destined for that port or not. Hub has no way of distinguishing which port a frame should be sent. Broadcasting results in lot of traffic on the network which lead to poor network response. If two PC simultaneously transmit there data packets and both are connected to a HUB, then collision will occur, so we can say, it creates a single collision domain. On the other hand all PCs connected to a hub will get a same message so a single broadcast domain will be created.
A 100/1000 Mbps hub must share its bandwidth with each and every one of its ports. So when only one PC is broadcasting, it will have access to the max available bandwidth. If, however, multiple PC’s are broadcasting, then that bandwidth will need to be divided between all of these systems, which will degrade the performance. They are usually Half-Duplex in nature.
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SWITCH
Hubs are capable of joining more than two PC but having some demerits like if two PC would want to communicate at a time then there would be a collision and the both PC would have to send the data once again. This shortcoming of Hub is overcame by Switches. Switches are intelligent devices which work on the Layer2 of the OSI model. Basically a switch keeps a record of MAC addresses of all the devices connected to it. Using this information, it builds a MAC address table. So when a frame is received, it knows exactly which port to send it to, which increases the network response time.
Basic Working Principle of Switch.
1. At the time of initializing the switch the MAC address table is yet to be built up. When a frame is send by some of the PC, it recognises the source MAC address and update the MAC address table.
2. If the destination is available in the MAC table then forward to the corresponding PC.
3. If the destination MAC address is not present in the table then forwards in all the port available expect the incoming one. The designated PC will respond for the data and it will send the acknowledge for the data received. This acknowledged data will be examined by the switch and the MAC address table would be up dated accordingly.
If two PC simultaneously transmit there data packets and both are connected to a SWITCH, then collision will not occur, so we can say, it creates a multiple collision domain.
The switch supports broadcast. Hence we can call switches create single broadcast domain and multiple collision domains.
A 100/1000Mbps switch will allocate a full 100/1000 Mbps to each of its ports. So regardless of the no of PC’s transmitting user will always have access to max amt of bandwidth. They are usually Full-Duplex in nature.
Switches are of two types 1) Managed
2) Unmanaged
Managed switch supports SNMP (Simple Network Management Protocol)
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Different switching
Principles:-1. Store-and-forward:- The switch fully receives all bits in the frame (store) before forwarding the frame (forward). This allows the switch to check the FCS before forwarding the frame. (FCS is in the Ethernet trailer.)
2. Cut-through:- The switch performs the address table lookup as soon as the destination address field in the header is received. The first bits in the frame can be sent out the outbound port before the final bits in the incoming frame are received. This does not allow the switch to discard frames that fail the FCS check. (FCS is in the Ethernet trailer.)
3. Fragment Free:- This performs like cut-through switching, but the switch waits for 64 bytes to be received before forwarding the first bytes of the outgoing frame. According to Ethernet specifications, collisions should be detected during the first 64 bytes of the frame; frames in error because of a collision will not be forwarded. The FCS still cannot be checked.
Bridge is another device like switch which also operates basing on the MAC address. But the Basic difference between the bridge and the switch is that bridge works on software bases, but the switch works on hardware basic. The Switch works on ASICs ( Application Specific Integrated Circuits)
ROUTER
Switch and the Hub can only interconnect devices in a single LAN. For interconnecting two LAN or two or more different networks anther device known as router is used. Its main job is to route ( sends ) packets to other networks and to do the routing ( establishing paths between networks ) it uses the IP address.
A router is typically connected to at least two networks, commonly two LAN’s or WAN’s or a LAN and its ISP’s network. Routers are located at gateways, the places where two or more networks connect. Routers to determine the best path for forwarding the packet are using forwarding tables.
It is a layer 3 device i.e it operates at network layer of OSI model. The working principle of the router is totally different from a switch. Router makes a table known as routing table, which contains all the IP address in the network, the information for IP address router obtains directly ( all configured IP address on it ) or indirectly ( from neighbour routers ). When a packet is received it compares the destination IP address of the packet with the available IP addresses in its Routing table. If the IP address is not available in the routing table then it simply discard the packet instead of flooding in all the ports like a switch.(Detailed Information about router in chap )
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Comparison between Hub, Bridge, Switch & Router
Feature Hub Bridge Switch Router
Number of 1 per
collision bridge 1 per switch router
domains 1 port port
interfac Forwards LAN e
broadcasts? 1 Yes Yes No
Yes; can be Forwards LAN
optimized for less
multicasts N/A Yes forwarding No
OSI layer used when making forwarding
decision N/A Layer 2 Layer 2 Layer 3
Store-and-Internal
forward,
cut-Store- through,
Store-processing and- FragmentFre
and-variants N/A forward e forward
Frame/packet fragmentation
allowed? N/A No No Yes
Multiple
allowed? N/A No No Yes
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