Data Link and Link Differences:
The link is a passive point-to-point physical line, and there is no other exchange node.
In addition to having a physical line, the data link must have some necessary communication protocols to control
The transmission of these data. If the hardware and software implemented to these protocols are added to the link,
It became a data link.
The main function of the data link layer:
Link management
Frame setting
flow control
Error control
Separate data and control information
Transparent transmission
Address
Stop protocol Stop-and-Wait Protocol
Principle: (Probably Description) A Send frame to b, and design the timer, in the specified time,
If A receives the Ack returned, it indicates that A is sent successful, then
One frame. If a confidous Ack returned in the specified time, there are two
Situation: 1 A Send frame failed; 2 B returned to the ACK failed.
For the first case, a retransmit the frame and re-press the timer. For the second
In the case, A will receive two identical frames if it takes retransmissions.
Allowed. What should I do at this time? Solution is to give the frame number.
Circular redundant inspection principle (not test requirements): Model 2 operation.
FCS frame inspection sequence continuous ARQ protocol
Working principle (probably description): Unlike the stop agreement, a is no longer sent to one frame at this time.
Until receiving the Ack returned. It is a continuous number of frames, when you encounter
A frame send timeout (failure), from this frame, it will increase the efficiency.
The sliding window is used to traffic control on the transmitting end. (Understanding Working Principles)
Select the retransmission ARQ protocol. . A fairly capacity cache space must be set at the receiving end.
Bitted link control procedures HDLC
HDLC frame structure
Sign F address A Control C Information INFO Frame Check Sequence FCS Sign F
Zero-bit filler method (What is the problem? How to solve?)
Point-to-point protocol PPP for the Internet
F 7e a ff c 03 protocol information part FCS F 7E
Similar to HDLC frame, only the protocol field
Several reasons for using PPP.
