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Lecture10 - Thursday May 1 Lab#2 Scores are posted Pick up...

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1 Thursday, May 1 Lab#2 Scores are posted Pick up Homework #2 Due now Questions? Hope you made a copy for yourself Lab #3 Report is due tomorrow before midnight TAs have office hours today/tomorrow Program #1 Due Friday, May 9 Evaluation criteria are posted
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2 Today’s topics More Transmission Control Protocol (TCP) Connection, handshake Flow control Congestion control
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3 TCP segment structure source port # dest port # 32 bits application data  (variable length) sequence number acknowledgement number Receive window Urg data pnter checksum F S R P A U head len not used Options (variable length,  padded to 32 bits) URG: urgent data  (generally not used) ACK: ACK # valid PSH: push data now (generally not used) RST, SYN, FIN: connection estab (setup, teardown commands) # bytes  rcvr willing to accept counting by bytes  of data (not segments!) Internet checksum (as in UDP)
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4 TCP header Source Port  (16 bits): Identifies source user process Destination  Port (16 bits): Identifies destination process Sequence Number  (32 bits): Sequence number of the first byte in the segment. If SYN is present, this is  the initial sequence number (ISN) and the first data byte is ISN+1. Ack number  (32 bits): Next byte expected Header Length  (4 bits): Number of 32-bit words in the header Reserved  (6 bits) Code bits  (6 bits): Urgent pointer field significant, ack field significant, push function, reset the  connection, synchronize the sequence numbers, no more data from sender Window   (16 bits): Will accept [Ack] to [Ack]+[window] Checksum   (16 bits): covers the segment plus a pseudo-header.  Includes the following fields from IP  header: source and dest adr, protocol, segment length. Protects from IP misdelivery. Urgent pointer  (16 bits): Points to the byte following urgent data. Lets receiver know how much  urgent data is coming. Options  (variable)  MSS, etc. Must be padded to 32 bits
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5 TCP Connection Establishment Three way handshake: Step 1:   client host sends TCP SYN segment  to server specifies initial seq # no data Step 2:   server host receives SYN, replies  with SYNACK segment server allocates buffers specifies server initial seq. # Step 3:  client receives SYNACK, replies  with ACK segment, which may contain  data client server SYN, ClientSeq# Connection request SYN, ACK, ServerSeq# Connection granted ACK, DATA ACK
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6 TCP Connection: tear down Closing a connection: Step 1:   client: closes socket sends TCP FIN control segment to  server   Step 2:   server: receives FIN,  replies with ACK closes connection,  sends FIN.  client server FIN close ACK FIN close
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