Guide to TCP/IP, Third Edition Chapter 6: Basic TCP/IP Services
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 Basic TCP/IP Services 2
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) Basic TCP/IP Services 3
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 Basic TCP/IP Services 4
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 Basic TCP/IP Services 5
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 Basic TCP/IP Services 6
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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 user s dynamic port to the server s FTP port Initiates FTP commands Monitors the data transfer process Basic TCP/IP Services 8
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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 Basic TCP/IP Services 12
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 Basic TCP/IP Services 13
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 Basic TCP/IP Services 14
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Active and Passive FTP In active mode Client connects from random TCP port with an address greater than 1023 to FTP server s 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 Basic TCP/IP Services 17
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 Basic TCP/IP Services 18
Telnet Elements (continued) NVT Considered a printer-keyboard device that receives bytes from the other host and prints the information The DO, DON T, WILL, WON T Structure 253 (0xFD)DO 254 (0xFE)DON T 251 (0xFB)WILL 252 (0xFC)WON T Basic TCP/IP Services 19
Telnet Sample Telnet Communications 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 Basic TCP/IP Services 20
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 t perform e-mail transfer services Basic TCP/IP Services 21
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SMTP Elements Sender-SMTP and Receiver-SMTP SMTP Commands and Extension SMTP Reply Codes Sender-SMTP and Receiver-SMTP processes Client or server e applications that support SMTP functionality Basic TCP/IP Services 23
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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 Basic TCP/IP Services 25
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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 Basic TCP/IP Services 27
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) Basic TCP/IP Services 28
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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 Basic TCP/IP Services 30
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 Basic TCP/IP Services 31
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 Basic TCP/IP Services 32
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 Basic TCP/IP Services 33
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 Basic TCP/IP Services 34
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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 Basic TCP/IP Services 36
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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 Basic TCP/IP Services 38
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 ti among mutually independent protocol stacks The Gatekeeper Basic TCP/IP Services 39
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 Basic TCP/IP Services 40
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 Basic TCP/IP Services 41
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 p Basic TCP/IP Services 42
Other Common TCP/IP-Based Echo (TCP and UDP) Services Quote of the Day (QOD) Character Generator (Chargen) Whois Trivial File Transfer Protocol (TFTP) Basic TCP/IP Services 43
Finger Other Common TCP/IP-Based Services (continued) Remote Procedure Call (RPC) Simple Network Management Protocol (SNMP) NetBIOS over TCP/IP Basic TCP/IP Services 44
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Decoding Application Layer Protocols Decoding TCP/IP Application layer traffic largely depends on two separate forms of analysis Understanding specific service s request/reply py 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 Basic TCP/IP Services 47
Summary Foundation upon which all TCP/IP Application layer services rest A request/reply py 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 Basic TCP/IP Services 48
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 Basic TCP/IP Services 49
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 Basic TCP/IP Services 50