Figure 2-4: General Message Organization, Continued Header Other Destination Message with Header Address only a header Field Field TCP supervisory messages are pure headers (there is no data field content to deliver) 2-11
2-11 Figure 2-4: General Message Organization, Continued Header Other Header Field Destination Address Field Message with only a header e.g. TCP supervisory messages are pure headers (there is no data field content to deliver)
Reliability
2. Reliability
Figure 2-5: Reliable Transmission Control Protocol (TCP)Session The Transmission Control Protocol (TCP)is an important standard in Internet transmission TCP Receiver acknowledges each correctly-received TCP segment If an acknowledgments is not received by the sender the sender retransmits the TCP message(called a TCP segment) This gives reliability: error detection and error correction 2-13
2-13 Figure 2-5: Reliable Transmission Control Protocol (TCP) Session • The Transmission Control Protocol (TCP) is an important standard in Internet transmission • TCP – Receiver acknowledges each correctly-received TCP segment. – If an acknowledgments is not received by the sender, the sender retransmits the TCP message (called a TCP segment) – This gives reliability: error detection and error correction
Figure 2-5: Reliable TCP Session, Continued Client PC Webserver TCP Process TCP Process 4.DatashttpRequest Carry 5.ACK(4) Http Req 6. Data n P Resp TCP Segment(Message)4 Carries an Http Request Segment 5 Acknowledges It Request-Response There is No need to resend Cycle for Data transfer 2-14
2-14 Figure 2-5: Reliable TCP Session, Continued Client PC TCP Process Webserver TCP Process 4. Data = HTTP Request 5. ACK (4) 6. Data = HTTP Response 7. ACK (6) Carry HTTP Req & Resp (4) Request-Response Cycle for Data Transfer TCP Segment (Message) 4 Carries an HTTP Request Segment 5 Acknowledges It There Is No Need to Resend
Figure 2-5: A TCP Session, Continued Client PC Webserver TCP Process TCP Process 8. daTa= Http Request(error) Ca 9. Data= Http Request (no Ack so Retransmit Http Req Resp (4) TCP Segment (Message)8 11. Data Is Lost in transmission There Is No Acknowledgment Error Handling 12 So the Sender Retransmits 2-15
2-15 Figure 2-5: A TCP Session, Continued Client PC TCP Process Webserver TCP Process Carry HTTP Req & Resp (4) 8. Data = HTTP Request (Error) 9. Data = HTTP Request (No ACK so Retransmit) 10. ACK (9) 11. Data = HTTP Response 12. ACK (11) Error Handling TCP Segment (Message) 8 Is Lost in Transmission There Is No Acknowledgment So the Sender Retransmits It