A data link layer function: Link management, transmission of information, flow control and error, exception handling.
Second, the data link layer flow control protocol:
1. Stop - flow control, etc. [deprecated]
2. The sliding window flow control (loop)
III. WAN data link layer transmission control procedure
1. The transmission control procedure for character
2. The bit-oriented type transmission control protocol:
Flag field F address field control field C A frame check sequence information field INFO flag field F
1Byte 1Byte 1Byte variable length 2Byte 1Byte
Flag field F: to achieve frame-level synchronization to indicate the beginning and end of the frame at the head and tail [have increased] flag field
Bit pattern: 01111110 (6 consecutive 1)
Zero-bit stuffing process - so that no data portions 6 consecutive one (1 in 5 consecutive fill behind a 0)
Originating raw data: 01011111100
After beginning treatment: 010111110100
After the receiving side processing: 01011111100
Control field (HDLC core): an information frame I, frame supervision S, unnumbered frame U
Frame Symbol: bit (1) wherein I is the frame control field flag is "0"
(2) signature S frame is the first bit of the control field is "1", the second is "0"
The value of the Type field (bits 3,4):
Type 100 (ready to receive)
Two types of 10 (receiver not ready)
Type three 01 (reject)
Type 4:11 (opt)
(2) wherein U flag is the first bit of the frame control field is "1", the second is also "1"
four. Three basic problem of data link layer protocol: encapsulated in a frame, transparent transmission, error detection
V. Ethernet MAC frame format
1.MAC frame format beginning 8 bytes is inserted, is first 7 bytes of preamble, a start frame delimiter byte (1010101011)
2. byte data portion 46-1500
3. no need to use an Ethernet frame end delimiter is not required to guarantee the transparent transmission of the byte inserted.