module14-tcp2V2

module14-tcp2V2 - TCP - Part II Relates to Lab 5. This is...

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1 TCP - Part II Relates to Lab 5. This is an extended module that covers TCP data transport, and flow control, congestion control, and error control in TCP.
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2 Interactive and bulk data transfer TCP applications can be put into the following categories bulk data transfer - ftp, mail, http interactive data transfer - telnet, rlogin TCP has heuristics to deal these application types. For interactive data transfer: Try to reduce the number of packets For bulk data transfer:
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3 Telnet session on a local network Argon.cs.virginia.edu Neon.cs.virginia.edu Telnet session from Argon to Neon This is the output of typing 3 (three) characters : Time 44.062449: Argon Neon: Push, SeqNo 0:1(1), AckNo 1 Time 44.063317: Neon Argon: Push, SeqNo 1:2(1), AckNo 1 Time 44.182705: Argon Neon: No Data, AckNo 2 Time 48.946471: Argon Neon: Push, SeqNo 1:2(1), AckNo 2 Time 48.947326: Neon Argon: Push, SeqNo 2:3(1), AckNo 2 Time 48.982786: Argon Neon: No Data, AckNo 3 Time 55.116581: Argon Neon: Push, SeqNo 2:3(1) AckNo 3 Time 55.117497: Neon Argon: Push, SeqNo 3:4(1) AckNo 3 Time 55.183694: Argon Neon: No Data, AckNo 4
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4 Interactive applications: Telnet Remote terminal applications (e.g., Telnet) send characters to a server. The server interprets the character and sends the output at the server to the client. For each character typed, you see three packets: 1. Client Server: Send typed character 2. Server Client: Echo of character (or user output) and acknowledgement for first packet 3. Client Server: Acknowledgement for second packet 1. send character 2. interpret character 3. send echo of character and/or output Host with Telnet client Host with Telnet server
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5 Why 3 packets per character? We would expect four packets per character: However, tcpdump shows this pattern: What has happened? TCP has delayed the transmission of an ACK character ACK of character ACK of echoed character echo of character ACK and echo of character
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6 Delayed Acknowledgement TCP delays transmission of ACKs for up to 200ms The hope is to have data ready in that time frame. Then, the ACK can be piggybacked with a data segment. Delayed ACKs explain why the ACK and the “echo of character” are sent in the same segment.
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7 Telnet session to a distant host argon.cs.virginia.edu tenet.cs.berkeley.edu Telnet session between argon.cs.virginia.edu and tenet.cs.berkeley.edu This is the output of typing nine characters : Time 16.401963: Argon Tenet: Push, SeqNo 1:2(1), AckNo 2 Time 16.481929: Tenet Argon: Push, SeqNo 2:3(1) , AckNo 2 Time 16.482154: Argon Tenet: Push, SeqNo 2:3(1) , AckNo 3 Time 16.559447: Tenet Argon: Push, SeqNo 3:4(1), AckNo 3 Time 16.559684: Argon Tenet: Push, SeqNo 3:4(1), AckNo 4 Time 16.640508: Tenet Argon: Push, SeqNo 4:5(1) AckNo 4 Time 16.640761: Argon Tenet: Push, SeqNo 4:8(4) AckNo 5 Time 16.728402: Tenet Argon: Push, SeqNo 5:9(4) AckNo 8
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module14-tcp2V2 - TCP - Part II Relates to Lab 5. This is...

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