Guide to TCP/IP, Second Edition1 Guide To TCP/IP, Second Edition Chapter 5 Transport Layer TCP/IP Protocols

Guide to TCP/IP, Second Edition2 Objectives Understand the key features and functions of the User Datagram Protocol (UDP) Explain the mechanisms that drive segmentation, reassembly, and retransmission for the Transmission Control Protocol (TCP) Choose between using UDP and TCP

Guide to TCP/IP, Second Edition3 Overview of UDP List of limitations of UDP –No reliability mechanism –No delivery guarantees –No connection handling –Identifies Application layer protocol conveyed –Checksum for entire message carried in UDP header –No buffering services –No segmentation

Guide to TCP/IP, Second Edition4 UDP—A Connectionless Transport Layer Protocol Connectionless protocols provide best-effort Connectionless protocols handle the following kinds of tasks: –Message Checksum –Higher-layer protocol identification

Guide to TCP/IP, Second Edition5 UDP Header Fields and Functions UDP header fields –Source Port Number Field –Well-Known Port Numbers (0 through 1023) –Registered Port Numbers (1024 through 49151) –Dynamic Port Numbers (49152 through 65535) –Destination Port Number Field Temporary ports referred as ephemeral ports

Guide to TCP/IP, Second Edition6 UDP Header Fields and Functions (cont.)

Guide to TCP/IP, Second Edition7 UDP Header Fields and Functions (cont.) Length Field –IP Header Length –IP Total Length –UDP Length Checksum Field –Pseudo-header

Guide to TCP/IP, Second Edition8 UDP Header Fields and Functions (cont.)

Guide to TCP/IP, Second Edition9 UDP Header Fields and Functions (cont.)

Guide to TCP/IP, Second Edition10 UDP Port Numbers and Processes

Guide to TCP/IP, Second Edition11 Overview of TCP Connection-oriented services Error recovery Sliding window mechanism End-to-end reliability Virtual connection –Handshake process

Guide to TCP/IP, Second Edition12 Overview of TCP (cont.)

Guide to TCP/IP, Second Edition13 TCP—A Connection-Oriented Protocol Connection-oriented protocols do the following: –Logical connection –Acknowledgements –Sequence number tracking –Timeout mechanism –Retry mechanism

Guide to TCP/IP, Second Edition14 TCP Startup Connection Process (TCP Handshake) One host initiates the handshake to another host to –Ensure the destination host is available –Ensure the destination host is listening on the destination port number –Inform the destination host of the initiator’s sequence number so that the two sides can track data as it is transferred

Guide to TCP/IP, Second Edition15 TCP Handshake

Guide to TCP/IP, Second Edition16 Handshake Packet #1

Guide to TCP/IP, Second Edition17 Handshake Packet #2

Guide to TCP/IP, Second Edition18 Handshake Packet #3

Guide to TCP/IP, Second Edition19 TCP Half-Open Connections Half-Open connections –SYN>>>>> –<<<<<ACK SYN Denial of Service (DoS) attack –Two-way handshake

Guide to TCP/IP, Second Edition20 TCP Keep-Alive Process Maintain the connection when there is no data traffic Disabled by default on Windows 2000 and Windows XP

Guide to TCP/IP, Second Edition21 TCP Connection Termination FIN and ACK flags TCP connection states

Guide to TCP/IP, Second Edition22 TCP Connection States

Guide to TCP/IP, Second Edition23 TCP Connection States (cont.)

Guide to TCP/IP, Second Edition24 TCP Sequence and Acknowledgment Process Each side of the connection selects its own starting sequence number Each side increments its sequence number value by the amount of data included in the outbound packet

Guide to TCP/IP, Second Edition25 TCP Error-Detection and Error-Recovery Process Retransmission timer Retransmission timeout (RTO) Round-trip time (RTT)

Guide to TCP/IP, Second Edition26 Retransmit Timer And Process

Guide to TCP/IP, Second Edition27 TCP Congestion Control Windowing Advertised window Current Window TCP buffer Four TCP congestion control mechanisms –Slow Start – Congestion Avoidance – Fast Retransmit – Fast Recovery

Guide to TCP/IP, Second Edition28 TCP Sliding Window (cont.)

Guide to TCP/IP, Second Edition29 TCP Header Fields and Functions TCP header fields –Source/Destination Port Number Field –Sequence Number Field –Acknowledgment Number Field –Data Offset (Field) –Flags Field –Window Size Field –TCP Checksum Field –Urgent Pointer Field –TCP Options Field(s)

Guide to TCP/IP, Second Edition30 TCP Header

Guide to TCP/IP, Second Edition31 Decoded TCP Header

Guide to TCP/IP, Second Edition32 TCP Flag Settings

Guide to TCP/IP, Second Edition33 TCP Flag Settings (cont.)

Guide to TCP/IP, Second Edition34 Choosing Between TCP and UDP TCP is robust and reliable UDP is not robust and reliable Use UDP when avoiding unneeded complexity, or improving overall performance

Guide to TCP/IP, Second Edition35 Chapter Summary Transport layer protocols come in two types: connectionless, which are lightweight, unreliable, and provide only best-effort delivery services; and connection-oriented, which provide robust, reliable end-to-end delivery services, including explicit acknowledgment, segmentation and reassembly of arbitrary-sized messages, connection negotiation and management mechanisms, and retransmission of missing or erroneous segments

Guide to TCP/IP, Second Edition36 Chapter Summary (cont.) Because connectionless protocols are lightweight, they outperform connection- oriented protocols due to lower internal message overhead, and having no need for control and management of message traffic (acknowledgments, retransmissions, congestion control, and so on)

Guide to TCP/IP, Second Edition37 Chapter Summary (cont.) The User Datagram Protocol, UDP, is the connectionless protocol associated with the TCP/IP protocol suite It is commonly associated with Application layer protocols and services, such as BOOTP, DHCP, SNMP, NFS, and RIP, that either provide their own reliability mechanisms, or do without such mechanisms

Guide to TCP/IP, Second Edition38 Chapter Summary (cont.) In keeping with its simple capabilities, the UDP header is short and simple, consisting primarily of a protocol identifier in the IP header, an optional checksum value, and source and destination port addresses for the Application layer protocols or processes on the sending and receiving ends of a transmission

Guide to TCP/IP, Second Edition39 Chapter Summary (cont.) The Transmission Control Protocol,TCP, is the heavyweight, connection-oriented protocol that helps name the TCP/IP protocol suite It remains associated with the majority of TCP/IP Application layer protocols, especially those, such as Telnet, FTP, and SMTP, where reliable data delivery is desirable

Guide to TCP/IP, Second Edition40 Chapter Summary (cont.) In keeping with its more diverse, more robust capabilities, the TCP header is longer and more complex, including a variety of flags, values, and message types used to deliver acknowledgments, manage traffic flow, request retransmissions, and negotiate connections between hosts

Guide to TCP/IP, Second Edition41 Chapter Summary (cont.) Appropriate (and historical) uses for UDP concentrate on Application layer services that manage their own reliability and connections, such as NFS, and on chatty protocols and services, such as DHCP, SNMP, or RIP The chatty protocols and services rely on simple controls and fail-safes, and broadcast of periodic transmissions to handle potential reliability, deliverability, or reachability problems

Guide to TCP/IP, Second Edition42 Chapter Summary (cont.) Appropriate (and historical) uses for TCP concentrate on providing reliable delivery of user services, such as terminal emulation (Telnet and remote utilities), file transfer (FTP), (SMTP), and news (NNTP), where potentially important data must be delivered whole and intact, or not at all (and flagged with an error message)