TCP/IP and OSI Model. Lecture 10 TCP. Host-to-Host Transport Layer. TCP/IP and OSI Model (Continued) TCP Basic (Continued) TCP -- Basic

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1 /IP and OSI Model Lecture 10 Kuang-hua Chen Department of Library and Information Science National Taiwan University 1 Language & Information Processing System, LIS, NTU 10-2 /IP and OSI Model (Continued) Host-to-Host Transport Layer Two Main approaches: UDP oth rely on IP to deliver datagram RIP OSPF Language & Information Processing System, LIS, NTU 10-3 Language & Information Processing System, LIS, NTU asic asic (Continued) was designed to provide a reliable end-to-end byte stream over an unreliable internetwork must furnish the reliability that most users want and that IP does not provide ll connections are full-duplex and point-topoint does not support multicasting and broadcasting The traffic can go in both directions at the same time Large data is broken into segments and sent separately. Segments can arrive in any order Discards duplicates. Provides flow control. Language & Information Processing System, LIS, NTU 10-5 Language & Information Processing System, LIS, NTU 10-6

2 Transport Layer Services to the Session Layer Error control Flow control Sequencing Physical Communication Channel Subnet Creation of Services oth the sender and receiver create end points (sockets) The socket has a number (address) IP address 16-bit number local to the host (port) port is the name for a TSP Data Link Layer Transport Layer Language & Information Processing System, LIS, NTU 10-7 Language & Information Processing System, LIS, NTU 10-8 Ports Packet Encapsulation Well-known ports Port numbers below 256 are for standard services FTP: port 21 TELNET: port 23 HTTP (World Wide Web) : port 80 data ytes 1 to 500 ytes 1 to 500 ytes 1 to 500Packet Packet Packet From: To: IP Packet Language & Information Processing System, LIS, NTU 10-9 Language & Information Processing System, LIS, NTU Header Header Format dd Port Numbers, packet Sequence Numbers, cknowledgement Numbers and other fields. Form a /IP "stream" - a connection established using handshake and error detection/control through positive acknowledgement. Header Length 6 bits Language & Information Processing System, LIS, NTU Language & Information Processing System, LIS, NTU 10-12

3 Pseudoheader Check Sum Use 1 s complement dd every 16 bits Include header, data, and pseudoheader Language & Information Processing System, LIS, NTU Language & Information Processing System, LIS, NTU Segment Three-way Handshake Remember the maximal length of IP packet is 65,535 The maximal data carried in a segment is 65, (IP header length) - 20 ( header length) segments without any data are legal and are commonly used for acknowledgments and control messages sends a SYN message to I'd like to set up a connection and I will start with sequence number s Replies with a SYN and CK message to Yes I will talk to you. sends an CK message to along with the first piece of data I got your CK so here's the start of my data. Language & Information Processing System, LIS, NTU Language & Information Processing System, LIS, NTU Connection Connection Establishment in Host 1 Host 2 Host 1 Host 2 SYN(SEQ=x) SYN(SEQ=x) SYN(SEQ=y) Time SYN(SEQ=y, CK=x+1) SYN(SEQ=y, CK=x+1) 3. ctive open 4. Open id 8. Open Success 1. Passive 2. Open open id 9. Open Success SYN(SEQ=x+1, CK=y+1) SYN(SEQ=x, CK=y+1) 5. SYN(SEQ=55) 6. SYN(SEQ=202, CK=56) 7. SYN(SEQ=56, CK=203) Language & Information Processing System, LIS, NTU Language & Information Processing System, LIS, NTU 10-18

4 Data Transfer in Graceful Close in 10. Send 30 bytes 15. Deliver 100 bytes 12. Deliver 30 bytes 13. Send 100 bytes 17. Close 23. Deliver 26. Terminate 150 bytes 18. Send 150 bytes 21. Closing 27. Terminate 22. Close 11. DT(SEQ=57, CK=203) 19. FIN(SEQ=88, CK=303) 14. DT(SEQ=203, CK=87) 20. DT(SEQ=303, CK=89) 24. FIN(SEQ=453, CK=89) 16. CK(SEQ=87, CK=303) 25. FIN(SEQ=89, CK=454) Language & Information Processing System, LIS, NTU Language & Information Processing System, LIS, NTU User Datagram Protocol (UDP) UDP (Continued) dds Port Numbers to IP addresses Port number refers to a specific application running on a host. e.g. SMTP uses Port 25 while Telnet uses Port 23. Result is a set of Packets No handshaking or error control lso called a "Connectionless" protocol Often referred to as "Unreliable" - meaning error control can't be relied upon. Useful for the following situations Overhead is a concern Small data requests such as queries Language & Information Processing System, LIS, NTU Language & Information Processing System, LIS, NTU UDP Header UDP Check Sum Use 1 s complement dd every 16 bits Include UDP header, UDP data, and pseudo-header for no checksum Language & Information Processing System, LIS, NTU Language & Information Processing System, LIS, NTU 10-24

5 /IP /IP Stack Language & Information Processing System, LIS, NTU Language & Information Processing System, LIS, NTU 10-26