Brief introduction
Network layer protocol data unit isIP datagramWhile working link layer is the network layer down to pay for the encapsulation of IP datagramsframeTransmitted to the link, and the received data frame is extracted in to the network layer.
Its main functions are:
1. encapsulates data frames, which are units of record of the data link layer
2. The transmission control frame processing including transmission errors, adjust the sending rate and the receiving isotropic match
3 in both networks establish a data link to provide access between the entities, maintain and release management.
2. Error Control
Communication system must have the ability to find errors, and to take action to correct the error control within the allowable range as small as possible, this process is error control
feedback retransmission: the receiver by checking the coding of the error can be determined in a whether an error has occurred during transmission. Once an error occurs, the retransmission feedback general method may be employed to correct.
Timer
If a frame transmission problems, have not successfully transmitted, the transmission process in order to avoid stagnation, the timer is typically introduced (the Timer) to define a recipient sending a return message interval. When the sender of a transmission and also starts a timer when the receiving side fails to receive the feedback information, i.e., the timer times out (the Timeout) within a defined time interval may be considered outgoing erroneous or lost frames, it to re-sent.
No.
Since the same frame data may be repeatedly transmitted a plurality of times, it may cause the receiver receives a plurality of times when the same frame and to transmit it to the network layer. To prevent this, a method may be employed for the transmission of a frame number, i.e., a number given to each frame, so that the receiver can be distinguished from the number of new frames is transmitted or retransmitted, which determines which Do not submit the received frame to the network layer.
flow control:
Due to differences in operating speed devices each using both the transceiver and the buffer memory space, the sender may appear larger than the transmission capacity of the phenomenon recipient receives capability, this time limit without making the appropriate transmission rate of the sender, the received time to the front frame frame will be continuously sent back to the "flooding", resulting in lost frames and errors.
Thus, the flow control is actually a sender control data traffic, the transmission rate so that it does not exceed the rate of the reception side. We need to know some rules so that the sender can then send the next frame under what circumstances, and under what circumstances must stop sending, waiting to receive some feedback before sending more. This is the flow control.
