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Chapter Overview

Chapter Overview. TCP/IP DoD model. Network Layer Protocols. Responsible for end-to-end communications on an internetwork Contrast with data-link layer protocols, which provide communications on the same local area network (LAN). TCP/IP is everywhere with networks. Web pages using TCP/IP

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Chapter Overview

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  1. Chapter Overview • TCP/IP • DoD model

  2. Network Layer Protocols • Responsible for end-to-end communications on an internetwork • Contrast with data-link layer protocols, which provide communications on the same local area network (LAN)

  3. TCP/IP is everywhere with networks • Web pages using TCP/IP • Database access can use TCP/IP • It started with DOD (tax payer’s $$) • In 1973 it is TCP/IP • In 1978 they became TCP and IP (two protocols) • Mostly done at UC Berkeley and shipped with its version of UNIX

  4. DoD model, OSI model and protocols

  5. Port Numbers and Sockets • A port number refers to a specific application or process running on a computer. • A socket is a combination of a port number and an IP address. • The Internet Assigned Numbers Authority (IANA) assigns well-known port numbers to common Internet applications. • The most commonly used port numbers are listed in the Services file on computers running TCP/IP.

  6. Process/Application Apps and Protocols

  7. Host to host layer protocols • Transmission Control Protocol (TCP) • User Datagram Protocol (UDP)

  8. TCP Characteristics • TCP is the acronym for Transmission Control Protocol. • TCP is • Connection oriented • Reliable • It is used to carry large amounts of data. • It provides services that Internet Protocol (IP) lacks. • TCP is defined in Request for Comments (RFC) 793.

  9. TCP Functions • Guaranteed delivery • Packet acknowledgment • Flow control • Error detection

  10. Segmentation • TCP splits application layer messages into datagram-sized segments and encapsulates each segment with its own header. • The collection of segments is called a sequence. • The destination system reassembles the segments into the original application layer messages . • The segmentation process is completely separate from the network layer fragmentation process.

  11. The TCP Message Format

  12. Control Bits

  13. Three-Way Handshake Functions • Verify that both computers are operating and ready to receive data • Exchange initial sequence numbers (ISNs) • Exchange maximum segment sizes (MSSs) • Exchange port numbers

  14. Three-Way Handshake Messages

  15. Transmitting Data • Information needed to transmit data: • Port number • Sequence number • MSS (Max segment size)

  16. Packet Acknowledgment • TCP implements packet acknowledgment by using the Sequence Number and Acknowledgment Number fields. • The Sequence Number field specifies the number of bytes transmitted. • The Acknowledgment Number field specifies the number of bytes received.

  17. Delayed Acknowledgments • TCP systems do not have to individually acknowledge every packet they receive. • The frequency of acknowledgment is left up to the individual TCP implementation.

  18. Positive and Negative Acknowledgments • With positive acknowledgment with retransmission, TCP systems acknowledge only the number of bytes they have received correctly. • With negative acknowledgment, the computer specifies the information that it has not received correctly. • All data beginning with the failed segment is retransmitted. • Messages that are not acknowledged are retransmitted.

  19. TCP Error Detection • TCP provides the only end-to-end error detection for the application layer data. • TCP computes a checksum based on • The TCP header • The application layer information in the TCP Data field • A pseudo-header created from some of the fields in the IP header

  20. TCP Checksum Value

  21. Flow Control • Flow control allows a receiving system to control the transmission rate of the sending system. • Each computer has a buffer for storing incoming packets. • When a computer transmits too quickly, the buffer on the receiving system can fill up, causing packets to be dropped. • TCP uses the Window field in its acknowledgment messages to implement flow control. • The Window value indicates how much buffer space the receiving system has available. • The sending system is permitted to transmit only the number of bytes specified in the Window field.

  22. Terminating the Connection

  23. UDP Characteristics • UDP is the acronym for User Datagram Protocol. • UDP is defined in RFC 768. • It is a connectionless protocol. • It is used primarily for brief request/reply transactions.

  24. The UDP Message Format

  25. TCP VS. UDP

  26. Port Numbers • In computer networking, a port is an application-specific or process-specific software construct serving as a communications endpoint used by Transport Layer protocols, such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). • Port + IP address  socket

  27. Well Known port numbers • < 1024 • Defined in RFC 3232

  28. IP Layer Protocals • IP (Internet Protocol) • Encapsulation • Addressing • Routing • Fragmentation • Protocol identification

  29. The IP Datagram Format http://freesoft.org/CIE/Course/Section3/7.htm

  30. ICMP • Internet Control Message Protocol • Router may use ICMP to send back Destination Unreachable message • Or Buffer Full message • Over hop limit message • A message informing the demise of a IP datagram • ping • traceroute/tracert

  31. ARP and RARP • Address Resolution Protocol (ARP) • Resolve IP addresses to Mac addresses by broadcast a ARP message • arp -a • Reverse Address Resolution Protocol (RARP) • From MAC to IP, for diskless systems

  32. Data Encapsulation • The wrapping of protocol info at each layer. • Each layer communicate ONLY WITH ITS PEER LAYER

  33. Data Encapsulation – Protocol Data Units

  34. Data Encapsulation

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