2te_Klasse nwt
- Ethernet Frame
- Header Size + trailer → 18 bytes
- Min size of Ethernet frame (Header + Payload[Packet] + Trailer) → 64 bytes
- 64 bytes - 18 bytes (header + trailer size) = 46 bytes
- → min payload(packet) → 46 bytes
- if the payload is less than that → padding bytes are added
- zb 34 btye packet + 12 byte padding 46 bytes
- Preamble and SFD Excluded form the Size
- Preamble and SFD
- used for syncronazation → prepare device to recieve rest of the data from the frame
- Preamble
- 7 long long (56bits)
- Alternating 1’s and 0’s
- 10101010 * 7
- Allows devices to syncronize their reciever clocks
- SFD
- Start Frame Delimiter
- 1 byte long (8bits)
- 10101011
- Marks the end of the Preamble and the beginning of the rest of the frame
- Destination/Source
- Indicate the devices sending and recieiving the frame
- MAC addr from sender and reciever
- MAC = Media Access control
- MAC addr 6 byte (48bit) → addr of the physical device
- Type or Length
- 2 byte (16bit) length
- ethernet-typen
- Value of 1500 or less → length of the encapsulated packet (in bytes)
- Value of 1536 or greater → Type of encapsulated packet (usaually IPv4 or 6) and the length is determined via other methods
- 0x0800(hex) = IPv4 → 2048 in dez
- 0x86DD(hex) = IPv6 → 34525 in dez
- Daten
- Fcs (Trailer)
- → Frame Check Sequence
- 4 bytes (32bit) in length
- detects currupted data by running a “CRC” algorithm over the received data
- CRC = Cyclic Redundancy Check
- Framestop