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U of I CS 438 - Lecture notes

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12/12/06 CS/ECE 438 - UIUC, Fall 2006 1TCP12/12/06 CS/ECE 438 - UIUC, Fall 2006 2TCP Adaptive RetransmissionAlgorithm - Original Theory Estimate RTT Multiply by 2 to allow for variations Practice Use exponential moving average (A = 0.1 to 0.2) Estimate = (A) * measurement + (1- A) * estimate Problem Did not handle variations well Ambiguity for retransmitted packets Was ACK in response to first, second, etc transmission?12/12/06 CS/ECE 438 - UIUC, Fall 2006 3TCP Adaptive RetransmissionAlgorithm – Karn-Partridge Algorithm Exclude retransmitted packets from RTTestimate For each retransmission Double RTT estimate Exponential backoff from congestion Problem Still did not handle variations well Did not solve network congestion problems aswell as desired12/12/06 CS/ECE 438 - UIUC, Fall 2006 4TCP Adaptive RetransmissionAlgorithm – Jacobson Algorithm Estimate variance of RTT Calculate mean interpacket RTT deviation to approximate variance Use second exponential moving average Deviation = (B) * |RTT_Estimate – Measurement| + (1–B) * deviation B = 0.25, A = 0.125 for RTT_estimate Use variance estimate as component of RTT estimate Next_RTT = RTT_Estimate + 4 * Deviation Protects against high jitter Notes Algorithm is only as good as the granularity of the clock Accurate timeout mechanism is important for congestion control12/12/06 CS/ECE 438 - UIUC, Fall 2006 5TCP ConnectionEstablishment 3-Way Handshake Sequence Numbers J,K Message Types Synchronize (SYN) Acknowledge (ACK) Passive Open Server listens forconnection from client Active Open Client initiates connectionto server12/12/06 CS/ECE 438 - UIUC, Fall 2006 5TCP ConnectionEstablishment 3-Way Handshake Sequence Numbers J,K Message Types Synchronize (SYN) Acknowledge (ACK) Passive Open Server listens forconnection from client Active Open Client initiates connectionto serverClient ServerTime flows downlisten12/12/06 CS/ECE 438 - UIUC, Fall 2006 5TCP ConnectionEstablishment 3-Way Handshake Sequence Numbers J,K Message Types Synchronize (SYN) Acknowledge (ACK) Passive Open Server listens forconnection from client Active Open Client initiates connectionto serverSynchronize (SYN) JClient ServerTime flows downlisten12/12/06 CS/ECE 438 - UIUC, Fall 2006 5TCP ConnectionEstablishment 3-Way Handshake Sequence Numbers J,K Message Types Synchronize (SYN) Acknowledge (ACK) Passive Open Server listens forconnection from client Active Open Client initiates connectionto serverSynchronize (SYN) JSYN K,acknowledge (ACK) J+1Client ServerTime flows downlisten12/12/06 CS/ECE 438 - UIUC, Fall 2006 5TCP ConnectionEstablishment 3-Way Handshake Sequence Numbers J,K Message Types Synchronize (SYN) Acknowledge (ACK) Passive Open Server listens forconnection from client Active Open Client initiates connectionto serverSynchronize (SYN) JSYN K,acknowledge (ACK) J+1ACK K+1Client ServerTime flows downlisten12/12/06 CS/ECE 438 - UIUC, Fall 2006 6TCP Connection Termination Message Types Finished (FIN) Acknowledge (ACK) Active Close Sends no more data Passive close Accepts no more data12/12/06 CS/ECE 438 - UIUC, Fall 2006 6TCP Connection Termination Message Types Finished (FIN) Acknowledge (ACK) Active Close Sends no more data Passive close Accepts no more dataClient ServerTime flows down12/12/06 CS/ECE 438 - UIUC, Fall 2006 6TCP Connection Termination Message Types Finished (FIN) Acknowledge (ACK) Active Close Sends no more data Passive close Accepts no more dataFinished (FIN) JClient ServerTime flows down12/12/06 CS/ECE 438 - UIUC, Fall 2006 6TCP Connection Termination Message Types Finished (FIN) Acknowledge (ACK) Active Close Sends no more data Passive close Accepts no more dataFinished (FIN) JACK J+1Client ServerTime flows down12/12/06 CS/ECE 438 - UIUC, Fall 2006 6TCP Connection Termination Message Types Finished (FIN) Acknowledge (ACK) Active Close Sends no more data Passive close Accepts no more dataFinished (FIN) JACK J+1Client ServerTime flows downFIN K12/12/06 CS/ECE 438 - UIUC, Fall 2006 6TCP Connection Termination Message Types Finished (FIN) Acknowledge (ACK) Active Close Sends no more data Passive close Accepts no more dataFinished (FIN) JACK J+1ACK K+1Client ServerTime flows downFIN K12/12/06 CS/ECE 438 - UIUC, Fall 2006 7TCP Connection Management (cont)TCP clientlifecycleTCP serverlifecycle12/12/06 CS/ECE 438 - UIUC, Fall 2006 8TCP State DescriptionsWait for network to discard related packetsTIME_WAITConnection closed by both sides simultaneouslyCLOSINGConnection closed locally and ACK’dFIN_WAIT_2Connection closed locallyFIN_WAIT_1Connection closed by peer, closed locally, await ACKLAST_ACKConnection closed by peerCLOSE_WAITConnection ready for data transportESTABLISHEDConnection request sentSYN_SENTConnection request receivedSYN_RCVDWaiting for incoming connectionLISTENDisconnectedCLOSED12/12/06 CS/ECE 438 - UIUC, Fall 2006 8TCP State DescriptionsWait for network to discard related packetsTIME_WAITConnection closed by both sides simultaneouslyCLOSINGConnection closed locally and ACK’dFIN_WAIT_2Connection closed locallyFIN_WAIT_1Connection closed by peer, closed locally, await ACKLAST_ACKConnection closed by peerCLOSE_WAITConnection ready for data transportESTABLISHEDConnection request sentSYN_SENTConnection request receivedSYN_RCVDWaiting for incoming connectionLISTENDisconnectedCLOSEDWait for network to discard related packetsTIME_WAITConnection closed by both sides simultaneouslyCLOSINGConnection closed locally and ACK’dFIN_WAIT_2Connection closed locallyFIN_WAIT_1Connection closed by peer, closed locally, await ACKLAST_ACKConnection closed by peerCLOSE_WAITConnection ready for data transportESTABLISHEDConnection request sentSYN_SENTConnection request receivedSYN_RCVDWaiting for incoming connectionLISTENDisconnectedCLOSED12/12/06 CS/ECE 438 - UIUC, Fall 2006 8TCP State DescriptionsWait for network to discard related packetsTIME_WAITConnection closed by both sides simultaneouslyCLOSINGConnection closed locally and ACK’dFIN_WAIT_2Connection closed locallyFIN_WAIT_1Connection closed by peer, closed locally, await ACKLAST_ACKConnection closed by peerCLOSE_WAITConnection ready for


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U of I CS 438 - Lecture notes

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