What is it ?

• It is a data-link layer protocol
• We use LAN tech
• Uses CSMA / CD
• Uses BUS and STAR topology

Frame Format

Preamble

• 56 constant bits (101010….10)
• Contains 7 bytes of altering 0’s and 1’s and alerts the receiving system that the frame is coming and enable it to synchronize its clock if its out of synchronization

SFD (Start Frame Delimiter)

• Also has constant bits
• It was alerting the receiver (preamble + SFD = 8 bytes)
• This field signals the beginning of the frame
• It warns the station that this is the last time for synchronization

Destination Address

• It is the MAC (Media Access Control) address
• It is 48-bits and contains the link layer address of the destination station to receive the packet

Source Address

• Contains link layer address of the sender of a packet
• It is 6 bytes

Type

• Defines upper-layer protocol whose packet is encapsulated in the frame
• This is used for multiplexing and demultiplexing

Data and Padding

• 46 Bytes
• 1500 Bytes
• If less than 46 then it is padded with extra 0’s
• Has a field that defines the length of data

CRC (Cyclic Redundancy Check)

• Contains error-detection information
• If receiver calculates CRC and finds that it is not 0 (corruption in transmission), then it discards the frame