18-03-2011, 06:30 PM
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 | M.Arsalan Qureshi | | Join Date: Oct 2008 Location: Garden Town, Multan Cantt
Posts: 616
Program / Discipline: BSTS Class Roll Number: 09-31 | |
 Data Link Control
Data Link Control
* Flow control is the regulation of the sender’s data rate so that the receiver buffer does not become overwhelmed. * Error control is both error detection and error correction. * In Stop-and-Wait ARQ, the sender sends a frame and waits for an acknowledgment from the receiver before sending the next frame. * In Go-Back-N ARQ, multiple frames can be in transit at the same time. If there is an error, retransmission begins with the last unacknowledged frame even if subsequent frames have arrived correctly. Duplicate frames are discarded. * In Selective Repeat ARQ, multiple frames can be in transit at the same time. If there is an error, only the unacknowledged frame is retransmitted. * Flow control mechanisms with sliding windows have control variables at both sender and receiver sites. * Piggybacking couples an acknowledgment with a data frame. * The bandwidth-delay product is a measure of the number of bits a system can have in transit. * HDLC is a protocol that implements ARQ mechanisms. It supports communication over point-to-point or multipoint links. * HDLC stations communicate in normal response mode (NRM) or asynchronous balanced mode (ABM). * HDLC protocol defines three types of frames: the information frame (I-frame), the supervisory frame (S-frame), and the unnumbered frame (U-frame). * HDLC handle data transparency by adding a 0 whenever there are five consecutive 1s following a 0. This is called bit stuffing.
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