Part_7_new_DLC

Part_7_new_DLC - Data Link Control Protocols EE450:...

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EE450, USC, Zahid 1 Data Link Control Protocols EE450: Introduction to Computer Networks Professor A. Zahid
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EE450, USC, Zahid 2 z Two physically connected devices: z Host-Router, Router-Router, Router- Host z Unit of data: frame application transport network link physical network link physical M M M M H t H t H n H t H n H l M H t H n H l frame physical link data link protocol adapter card Data Link Layer
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EE450, USC, Zahid 3 Data Link Layer Services z Framing z Encapsulate packet into frame, adding header/trailer z Establish frame synchronization z z Errors caused by signal attenuation, noise. z Receiver detects presence of errors: Receiver drops frame Receiver requests retransmission (ARQ) Receiver corrects errors (discussed in EE568) z Flow Control z Ensuring the sender does not overwhelm the receiver (i.e., preventing buffer overflow)
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EE450, USC, Zahid 4 Frame Transmission Model Source Destination Frame 1 fr a m e 1 A C K 2 ACK Transmission Time ACK Propagation Delay Frame Propagation Delay Frame Transmission Time t tran < t prop ACK t tran > t prop
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EE450, USC, Zahid 5 Typical Frame Structure We shall see that the above structure does not work in a Multipoint link (like in LANs)
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EE450, USC, Zahid 6 Frame Synchronization z A special pattern, called a Flag (01111110) appears at the beginning and the end of the frame z Receiver hunts for flag sequence to synchronize z Bit stuffing used to avoid confusion with data containing 01111110
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This note was uploaded on 12/29/2009 for the course EE 450 at USC.

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Part_7_new_DLC - Data Link Control Protocols EE450:...

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