tailieunhanh - Lecture Digital communication systems - Lecture 22

The main contents of this chapter include all of the following: Defining advertising, a brief history of advertising, advertising in the digital age, organization of the consumer advertising industry, producing advertising, economics, business-to-business advertising. | 12 3 12 Fall 2012 Lecture 22 Sliding window protocol analysis Bandwidth-delay product queues Packet loss performance Little s law Fall 2012 Lecture 22 Slide 1 Sliding Window Handling Packet Loss window 1-5 window 2-6 1 2 3 4 5 6 Sndr Rcvr 1 p1 p3 ằ Fall 2012 Lecture 22 Slide 2 Sliding Window Handling Packet Loss Data ACK sequence trace Data packet 2 is lost. The receiver must save packets all later packets until packet 2 arrives to deliver them to the application in proper order. Note that with our definition of the window there s no limit to the number of packets that might arrive out of order. Q Can the receiver discard these later packets 3 4 . 12 560 680 660 640 620 600 580 trace2-seq trace2-ack X l W ndow. - RTT x X . RTO Rxmi t - AC X X pac 0 Ks for rxmit kets most ted probably o 800 820 840 860 880 900 Time ms Lecture 22 Slide 5 Fall 2012 Lecture 22 Slide 3 Fall 2012 1 12 3 12 Sliding Window Implementation Transmitter - Each packet includes a sequentially increasing sequence number - When transmitting save xmit time packet on un-ACKed list - Transmit packets if len un-ACKed list window size W - When acknowledgement ACK is received from the destination for a particular sequence number remove the corresponding entry from un-ACKed list - Periodically check un-ACKed list for packets sent awhile ago Retransmit update xmit time in case we have to do it again awhile ago xmit time now timeout Receiver - Send ACK for each received packet reference sequence number - Deliver packet payload to application in sequence number order Save delivered packets in sequence number order in local buffer remove duplicates . Discard incoming packets which have already been delivered caused by retransmission due to lost ACK . Keep track of next packet application expects. After each reception deliver as many in-order packets as possible. Little s Law n t pkts at time t in queue C D E F G G . Bxi pXJ dF dd H A XXu4-----------D ------nuXiGn Ir a B C D E í F ĨGỊ