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Guide to TCP/IP, Third Edition

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Title: Guide to TCP/IP, Third Edition


1
Guide to TCP/IP, Third Edition
  • Chapter 5
  • Transport Layer TCP/IP Protocols

2
Objectives
  • Understand the key features and functions of the
    User Datagram Protocol
  • Explain the mechanisms that drive segmentation,
    reassembly, and retransmission for the
    Transmission Control Protocol
  • Choose between using User Datagram Protocol and
    Transmission Control Protocol

3
UDP A Connectionless Transport Layer Protocol
  • Connectionless protocols
  • Provide the simplest kind of transport services
  • UDP
  • Used by applications that contain their own
    connection oriented timeout values and retry
    counters
  • Runs up to 40 percent faster than TCP

4
UDP A Connectionless Transport Layer Protocol
(continued)
  • Connectionless protocols handle the following
    kinds of tasks
  • Message checksum
  • Higher-layer protocol identification

5
Overview of UDP
  • UDP limitations
  • No reliability mechanisms
  • No delivery guarantees
  • No connection handling
  • Identifies Application layer protocol conveyed
  • Checksum for entire message carried in UDP header
  • No buffering services
  • No segmentation

6
UDP Header Fields and Functions
  • UDP headers main function
  • To define the process or application that is
    using the IP and UDP Network and Transport layers
  • UDP header fields
  • Source Port Number field
  • Destination Port Number field
  • Length field
  • Checksum field

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8
UDP Header Fields and Functions (continued)
  • Source Port Number field
  • Defines the application or process that sends the
    packet using the UDP header
  • Well-known port numbers (0 Through 1023)
  • Assigned to core services that systems offer
  • Registered port numbers (1024 Through 49151)
  • Assigned to industry applications and processes
  • Dynamic ports
  • Used as temporary ports for specific
    communications while they are underway

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10
UDP Header Fields and Functions (continued)
  • Destination Port Number Field
  • Defines destination application or process that
    uses the IP and UDP headers
  • Length field
  • Defines the length of the packet from the UDP
    header to the end of valid data
  • Checksum field is optional

11
UDP Port Numbers and Processes
  • UDP and TCP
  • Use port numbers to define the source and
    destination processes or applications
  • By default
  • Windows 2000 and Windows XP support up to 5,000
    ports

12
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14
TCP A Connection-Oriented Protocol
  • Functions of connection-oriented protocols
  • Create a logical connection directly between two
    peers on an internetwork
  • Track the transfer of data and ensure it arrives
    successfully
  • Use sequence number tracking
  • Have a timeout mechanism
  • Have a retry mechanism

15
Overview of TCP
  • TCP offers connection-oriented services with
  • Sequencing, error recovery
  • Sliding window mechanism
  • TCP hosts
  • Create a virtual connection with each other using
    a handshake process
  • TCP
  • Transfers data as a continuous stream of bytes
  • Maximum TCP segment size is 65,495 bytes

16
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17
TCP Startup Connection Process
  • Begins with handshake between two hosts
  • 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 destination host of initiators sequence
    number

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23
TCP Half-Open Connections
  • Occur when the handshake process does not end
    successfully with a final ACK
  • Half-open connection communication sequence
    occurs in the following order
  • SYN gtgtgtgtgt
  • ltltltltlt ACK SYN
  • ltltltltlt ACK SYN
  • ltltltltlt ACK SYN

24
TCP Keep-Alive Process
  • Can maintain connection when there is no data
    sent across the wire
  • TCP keep-alives
  • Disabled by default on Windows 2000, Windows
    Server 2003, and Windows XP
  • KeepAliveTime setting
  • Defines how long to wait before sending the first
    TCP keep-alive packet

25
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26
TCP Connection Termination
  • Requires four packets
  • Host 1
  • Sends a TCP packet with the FIN and ACK flags set
  • Host 2
  • Sends an ACK in response
  • Then sends a TCP packet with FIN and ACK flags
    set
  • Host 1
  • Returns ACK response

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29
TCP Sequence and Acknowledgment Process
  • Guarantees that packets are ordered properly and
    protects against missing segments
  • During handshake process
  • Each side of connection selects its own starting
    sequence number
  • Each side increments its sequence number value by
    the amount of data included in the outbound packet

30
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32
TCP Error-Detection and Error-Recovery Process
  • Retransmission timer
  • First error-detection and error-recovery
    mechanism
  • Retransmission timeout (RTO)
  • Value specified by timer
  • Retransmission operation increments
  • 1st retransmit RTO seconds
  • 2nd retransmit 2 x RTO seconds
  • 3rd retransmit 4 x RTO seconds
  • 4th retransmit 8 x RTO seconds
  • 5th retransmit 16 x RTO seconds

33
TCP Congestion Control
  • Congestion
  • The overloading of the network or a receiver
  • Overloading of the network
  • Occurs when there is too much data on the network
    medium
  • Overloading a receiver
  • Occurs when the number of data bytes is greater
    than the advertised window
  • Current window
  • Always the lesser of what the network and
    receiver can handle

34
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35
TCP Congestion Control (continued)
  • TCP has four defined congestion control
    mechanisms
  • Slow Start
  • Congestion Avoidance
  • Fast Retransmit
  • Fast Recovery

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38
TCP Sliding Window
  • Used to determine the amount of unacknowledged
    data that can go out on the wire from any sender
  • Nagle algorithm
  • When small data segments are being sent, but not
    acknowledged, no other small segments can be sent
  • Silly Window Syndrome (SWS)
  • Caused when enough data is sent to a TCP host to
    fill its receiver buffer
  • Puts receiver in a zero-window state

39
TCP Header Fields and Functions
  • Source Port Number Field
  • Destination Port Number Field
  • Sequence Number Field
  • Acknowledgment Number Field
  • Header Length Field

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43
TCP Header Fields and Functions (continued)
  • Window Size Field
  • TCP Checksum Field
  • Urgent Pointer Field
  • TCP Options Field(s)

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46
Choosing Between TCP and UDP
  • Because TCP is robust and reliable
  • It carries a lot of baggage, including
  • Additional header fields
  • Explicit meta-messages in the form of TCP
    messages
  • For some lightweight services, such as Microsoft
    Messenger Service
  • TCP is overkill and UDP is used instead
  • TCP
  • No longer as important as it once was because
  • Long-haul and local area networks have
    significantly increased speed, capacity, and
    reliability

47
Summary
  • Transport layer protocols come in two types
  • Connectionless and connection-oriented
  • User Datagram Protocol
  • The connectionless protocol associated with
    TCP/IP protocol suite
  • UDP header is short and simple, consisting of
  • A protocol identifier in the IP header
  • An optional checksum value
  • Source and destination port addresses

48
Summary (continued)
  • Transmission Control Protocol
  • Heavyweight, connection-oriented protocol that
    helps name the TCP/IP protocol suite
  • TCP header
  • Longer and more complex,
  • Includes a variety of flags, values, and message
    types

49
Summary (continued)
  • Appropriate (and historical) uses for UDP
  • Concentrate on Application layer services that
    manage their own reliability and connections
  • Appropriate (and historical) uses for TCP
  • Concentrate on providing reliable delivery of
    user services
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