Ethernet 802

1. ETHERNET IEEE802.3
WIRED LANS

2. • Ethernet is a packet switching LAN technology that defines the way of
connecting computers together in a LAN using physical and Data link
layers.

3. ETHERNET EVOLUTION THROUGH FOUR
GENERATIONS

4. IEEE 802.3 MAC FRAME
Frame length: Minimum: 64 bytes (512 bits)
Maximum: 1518 bytes (12,144 bits)

5. MINIMUM AND MAXIMUM LENGTH

6. • Preamble: 56bits of alternating1s and 0s to help the host to
synchronize
• Start of Frame limiter:8 bits 10101011
• DA destination address
• SA Source address
• Length/Type of PDU
Min.data length: 46bytes
Max. data length:1500 bytes
• CRC- Cyclic Redundancy Check

7. ADDRESSING
Each station of an Ethernet network has its own Adaptor or Network Interface Card (NIC) which provides 6byte
physical or hardware address
Types: 1. Unicast addressing 2.Multicast addressing 3. Broadcast addressing
The least significant bit of the first byte defines the type of address. If the bit is 0,
the address is unicast; otherwise, it is multicast.
The broadcast destination address is a special case of the multicast address in
which all bits are 1s.

8. Access method
MAC is an algorithm that controls access to a shared Ethernet link.
• To avoid collision, Ethernet uses an access mechanism.
• CSMA/CD - 1G 10Mbps Ethernet
• MAC layer ism responsible for the operation of CSMA/CD access anf
framing
• Operation
• (i) Any station must use carrier sensing to listen in order to determine
whether the line is idle or busy.
• If the line is idle – transmission can commence immediately
• If the line is busy – signalling process is repeated again and again until
the transmission line is free for transmission

9. • (ii)During the data transmission, if it detects that another station is
also transmitting then the station uses collision detection mechanism
to check the line for extremely high voltages that indicates a collision.
If a collision is detected, the station quits the current transmission
and waits for a predefined amount of time until the line clears, then
sends the data again.
• Efficiency of standard Ethernet is defined as the ratio of the time
used by a station to send data to the time the medium is occupied by
the station
• Efficiency =1/(1+6.4xa)where a is the propogation delay/Transmission
delay

10. CATAGORIES OF STANDARD ETHERNET

11. Encoding in a Standard Ethernet
implementation

12. 10Base5 implementation

13. 10Base2 implementation

14. 10Base-T implementation

15. 10Base-F implementation

17. • In the full-duplex mode of Gigabit Ethernet, there is no collision; the
maximum length of the cable is determined by the signal attenuation
in the cable.

18. Encoding in Gigabit Ethernet implementations