Hardware used in the hosts

Posted by AJ × 08:10

NICs

Adapters to connect devices to a network

Perform:

• framing

• monitor the medium for transmissions

• capture data from the medium and pass them to their hosts nodes for processing

• check errors

• responsible for token passing

Also perform layer-1 function: convert bits to physical signals

• NIC works in two modes:

– General mode

– Promiscuous mode

• In general mode, the Ethernet card of the computer will allow following types of

packets:

– Packets send to the computer.

– Broadcast Packet

– Multicast packet and if computer is part of that multicast group.

• In promiscuous mode, the Ethernet card of the computer will allow all the packets

that it receives.

Limitations of layer 1

• Cannot organize streams of bits.

• Cannot name or identify computers.

• Cannot communicate with the upper-level layers.

• Cannot decide which computer will transmit binary data.

And hence the layer 2 provides the following functions

• Layer 2 uses framing to organize or group the bits.

• Layer 2 uses an addressing process to identify computers.

• Layer 2 uses Logical Link Control (LLC) to communicate with the upper-level

layers.

• Layer 2 uses Media Access Control (MAC) to decide which computer will transmit.

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