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Guide to TCP/IP, Third Edition

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Title: Guide to TCP/IP, Third Edition Created Date: 9/27/2002 11:29:22 PM Document presentation format: On-screen Show Other titles: Times New Roman Arial Default ... – PowerPoint PPT presentation

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Title: Guide to TCP/IP, Third Edition


1
Guide to TCP/IP, Third Edition
  • Chapter 6
  • Basic TCP/IP Services

2
Objectives
  • Understand how TCP/IP Application layer protocols
    and services work
  • Explain the capabilities, message types, and
    request/reply architectures for basic TCP/IP
    services
  • Discuss real-time streaming protocols (MSN
    Messenger and VoIP) for messaging and telephony
    applications

3
Objectives (continued)
  • Understand the operations of other basic TCP/IP
    services
  • Explain how to decode packets that contain
    Application layer protocols, and how to relate
    message types or other similar information to the
    kinds of requests and replies moving between a
    client and a server (or between hosts in general)

4
How Application Layer IP Protocols Work and Behave
  • Fundamental behavior of TCP/IP Application layer
    protocols depends on
  • Specifications for the message structures that
    the protocol or service supports
  • Definition of a well-known port address on which
    servers listen for service requests
  • Availability of appropriate software components

5
How Application Layer IP Protocols Work and
Behave (continued)
  • Request/reply messages
  • Types of messages that generally occur within
    TCP/IP Application layer services
  • Request messages
  • Used by clients to request services
  • Reply messages
  • Used by servers to reply to messages
  • Server-to-server traffic
  • Server-specific information is replicated from
    one server to another

6
Understanding FTP
  • FTP
  • Offers a method for transferring files over a
    connection-oriented transport, or TCP
  • Key components of an FTP communication
  • User interface (UI)
  • Protocol interpreter (PI)
  • FTP commands
  • Data transfer process (DTP)
  • Files transferred
  • TCP transport
  • TCP-based command connection
  • TCP-based data transfer connection

7
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8
FTP User Interface
  • Offers the visual front end to the user
  • Third-party products
  • Offer an FTP client application with a graphical,
    intuitive interface
  • Protocol Interpreter (PI)
  • Interprets commands
  • Initiates control connection from users dynamic
    port to the servers FTP port
  • Initiates FTP commands
  • Monitors the data transfer process

9
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10
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11
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12
FTP Elements
  • Data Transfer Process (DTP)
  • Moves data across the data connection only
  • File System
  • Files at either end of an FTP communication may
    consist of various formats
  • TCP Transport
  • FTP relies on TCP to
  • Establish the underlying connection
  • Track the order of packets
  • Define and adjust the data transfer window

13
FTP Elements (continued)
  • TCP-based Command Connection
  • Runs over TCP
  • Created automatically when
  • FTP connection is established in response to open
    command from FTP client
  • TCP-based Data Transfer Connection
  • Runs over TCP
  • Created by the server by default

14
Sample FTP Communications
  • FTP
  • Application layer protocol that relies on TCP
  • Commands immediately follow the FTP header
  • RFC 959
  • Has complete list of FTP protocol commands

15
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17
Active and Passive FTP
  • In active mode
  • Client connects from random TCP port with an
    address greater than 1023 to FTP servers command
    port, port 21
  • Passive FTP
  • Developed to sidestep issue of an apparent server
    connection initiation
  • Client initiates connections for both the command
    port and data port
  • Not supported by some FTP clients

18
Understanding Telnet
  • Telnet
  • Offers a bidirectional byte-oriented
    communication
  • Uses well-known port 23 on the server side
  • Uses dynamic port number on the client side
  • Telnet Elements
  • Telnet hosts exchange information about options
    that they support

19
Telnet Elements (continued)
  • NVT
  • Considered a printer-keyboard device that
    receives bytes from the other host and prints the
    information
  • The DO, DONT, WILL, WONT Structure
  • 253 (0xFD)DO
  • 254 (0xFE)DONT
  • 251 (0xFB)WILL
  • 252 (0xFC)WONT

20
Sample Telnet Communications
  • Telnet
  • Information immediately follows the TCP header
  • Remains an important and widely used TCP/IP
    service
  • Stelnet
  • Becoming increasingly available
  • Secure Sockets Layer (SSL) interface
  • Used to encrypt traffic between a Telnet client
    and a Telnet server

21
Understanding SMTP
  • Simple Mail Transfer Protocol (SMTP)
  • Most widely used protocol for sending electronic
    mail (e-mail) on the Internet
  • Sends and receives e-mail messages through
  • Sender-SMTP process
  • Receiver-SMTP process that perform e-mail
    transfer services

22
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23
SMTP Elements
  • Sender-SMTP and Receiver-SMTP
  • SMTP Commands and Extension
  • SMTP Reply Codes
  • Sender-SMTP and Receiver-SMTP processes
  • Client or server applications that support SMTP
    functionality

24
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25
Sample SMTP Communications
  • SMTP commands and reply codes
  • Immediately follow the TCP header
  • SMTP commands
  • Occur behind the scenes in some e-mail clients
    and some server-to-server mail transfers on the
    Internet
  • Majority of e-mail clients today
  • Use SMTP to send outgoing mail through some
    nearby SMTP server

26
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27
Understanding HTTP
  • Hypertext Transfer Protocol (HTTP)
  • Application layer protocol
  • Provides distributed information from various
    hypermedia systems
  • Has been in use on the Web since 1990
  • Uses a request/response model

28
HTTP Elements
  • HTTP clients
  • Send HTTP requests that contain a method that
    indicates what the client wants
  • HTTP servers
  • Respond with a numeric code
  • URI
  • Combination of a Uniform Resource Locator (URL)
    and a Uniform Resource Name (URN)

29
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30
HTTP Elements (continued)
  • HTTP methods
  • Commands that the HTTP client issues to the HTTP
    server
  • Status codes
  • Sent by HTTP server to indicate success or
    failure of request

31
Sample HTTP Communications
  • HTTP commands and status codes
  • Immediately follow the TCP header
  • HTTPS protocol
  • Represents a secure implementation of HTTP that
    incorporates use of SSL
  • TCP port 443
  • Assigned to HTTP protocol that uses TCP with
    Transport layer security over SSL
  • UDP port 443
  • Assigned to HTTP protocol that uses UDP with
    Transport layer security over SSL

32
Understanding MSN Messenger
  • MSN Messenger
  • Proprietary protocol specification
  • Handles audio and video applications and can be
    embedded within other protocols
  • MSN Messenger Elements
  • Possesses one of the largest subscriber bases in
    the world
  • Serves as a presence information provider

33
Obtaining and Using MSN Messenger
  • MSN Messenger
  • Readily available at no charge online at
    messenger.msn.com
  • Four fundamental entities define the MSN
    Messenger protocol architecture
  • The principal (or client) application
  • Dispatch server
  • Notification server
  • Switchboard server

34
MSN Messenger Commands
  • To reach a broad audience of subscribers
  • MSN Messenger protocol encodes character values
    outside the printable ASCII range
  • Principal and server commands
  • Three-letter abbreviations, followed by any
    number of specified parameters
  • During initialization phase
  • Commands sent between principal and server, occur
    synchronously

35
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36
Sample MSN Messenger Communications
  • Authentication procedures for MSN Messenger
    Services begin with dispatcher
  • Dispatcher
  • Negotiates an appropriate protocol version and
    format for each connection
  • Protocol revision 13
  • Provides full support for offline instant
    messaging

37
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38
Understanding VoIP
  • Voice over Internet Protocol (VoIP)
  • Describes the properties and procedures for
    routing voice conversations across the Internet
  • Responsible for transporting analog voice streams
    using digital signaling

39
VoIP Elements
  • Four primary entities involved in a
    H.323-basedVoIP communications network
  • The terminals, or voice/video/data clients
  • A Multipoint Control Unit (MCU) for bridging
    videoconference connections
  • The Gateway (GW) device for translating among
    mutually independent protocol stacks
  • The Gatekeeper

40
VoIP Elements (continued)
  • Session Initial Protocol (SIP)
  • Standard for initiating, modifying, or
    terminating interactive users sessions
  • Often used in tandem with H.323 for Voice over IP
    applications
  • H.323 protocol suite
  • Blanket specification for establishing real-time,
    streaming, qualitative multimedia communications
  • H.245
  • Defines control protocol for multimedia
    communication

41
VoIP Elements (continued)
  • H.235
  • Provides coverage of security and encryption for
    H.323 and H.245
  • H.450
  • Describes the supplementary services for H.323
    networks
  • H.239
  • A recommendation for relaying communications
    across different network media
  • Q.931
  • Documents the protocol and protocol state machine
    for ISDN connections

42
Sample VoIP Communications
  • Advantages of digitizing voice signals for
    transmission over TCP/IP
  • Better control can be exercised over the digital
    format
  • A digital signal is more forgiving of
    noise-bearing transmissions than an analog signal
  • VoIP communications avoid the costs associated
    with pay-per-usage

43
Other Common TCP/IP-Based Services
  • Echo (TCP and UDP)
  • Quote of the Day (QOD)
  • Character Generator (Chargen)
  • Whois
  • Trivial File Transfer Protocol (TFTP)

44
Other Common TCP/IP-Based Services (continued)
  • Finger
  • Remote Procedure Call (RPC)
  • Simple Network Management Protocol (SNMP)
  • NetBIOS over TCP/IP

45
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46
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47
Decoding Application Layer Protocols
  • Decoding TCP/IP Application layer traffic largely
    depends on two separate forms of analysis
  • Understanding specific services request/reply
    messages
  • Learning how to recognize related headers and
    payload information
  • Learning to assemble multiple lower-layer packets
  • To reconstitute Application layer messages when
    payloads exceed MTU for a single packet

48
Summary
  • Foundation upon which all TCP/IP Application
    layer services rest
  • A request/reply message architecture
  • Certain client/server Application layer services
  • Involve server-to-server traffic
  • FTP
  • A file transfer service
  • Telnet
  • Provides a method to log on and access the
    command line on a remote computer using TCP/IP

49
Summary (continued)
  • SMTP
  • Provides store and forward services for e-mail
    messages
  • HTTP
  • Provides the underpinnings for the World Wide Web
  • MSN Messenger and Voice over IP (VoIP)
    communications
  • Provide mechanisms to set up, manage, and tear
    down ongoing communications using TCP

50
Summary (continued)
  • Other common TCP/IP Application layer services
  • Echo, Chargen
  • QOD, TFTP, Finger
  • Remote Procedure Call
  • NetBIOS over TCP/IP
  • SNMP
  • Understanding how to decode Application layer
    protocols
  • Means learning how to identify and interpret
    request and reply messages
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