Guide to TCP/IP, Third Edition : Guide to TCP/IP, Third Edition Chapter 6:
Basic TCP/IP Services
Objectives : 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
Objectives (continued) : Basic TCP/IP Services 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)
How Application Layer IP Protocols Work and Behave : Basic TCP/IP Services 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
How Application Layer IP Protocols Work and Behave (continued) : Basic TCP/IP Services 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
Understanding FTP : Basic TCP/IP Services 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
Slide 7 : Basic TCP/IP Services 7
FTP User Interface : Basic TCP/IP Services 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 user’s dynamic port to the server’s FTP port
Initiates FTP commands
Monitors the data transfer process
Slide 9 : Basic TCP/IP Services 9
Slide 10 : Basic TCP/IP Services 10
Slide 11 : Basic TCP/IP Services 11
FTP Elements : Basic TCP/IP Services 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
FTP Elements (continued) : Basic TCP/IP Services 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
Sample FTP Communications : Basic TCP/IP Services 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
Slide 15 : Basic TCP/IP Services 15
Slide 16 : Basic TCP/IP Services 16
Active and Passive FTP : Basic TCP/IP Services 17 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
Understanding Telnet : Basic TCP/IP Services 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
Telnet Elements (continued) : Basic TCP/IP Services 19 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
Sample Telnet Communications : Basic TCP/IP Services 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
Understanding SMTP : Basic TCP/IP Services 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
Slide 22 : Basic TCP/IP Services 22
SMTP Elements : Basic TCP/IP Services 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
Slide 24 : Basic TCP/IP Services 24
Sample SMTP Communications : Basic TCP/IP Services 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
Slide 26 : Basic TCP/IP Services 26
Understanding HTTP : Basic TCP/IP Services 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
HTTP Elements : Basic TCP/IP Services 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)
Slide 29 : Basic TCP/IP Services 29
HTTP Elements (continued) : Basic TCP/IP Services 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
Sample HTTP Communications : Basic TCP/IP Services 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
Understanding MSN Messenger : Basic TCP/IP Services 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
Obtaining and Using MSN Messenger : Basic TCP/IP Services 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
MSN Messenger Commands : Basic TCP/IP Services 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
Slide 35 : Basic TCP/IP Services 35
Sample MSN Messenger Communications : Basic TCP/IP Services 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
Slide 37 : Basic TCP/IP Services 37
Understanding VoIP : Basic TCP/IP Services 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
VoIP Elements : Basic TCP/IP Services 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
VoIP Elements (continued) : Basic TCP/IP Services 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
VoIP Elements (continued) : Basic TCP/IP Services 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
Sample VoIP Communications : Basic TCP/IP Services 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
Other Common TCP/IP-Based Services : Basic TCP/IP Services 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)
Other Common TCP/IP-Based Services (continued) : Basic TCP/IP Services 44 Other Common TCP/IP-Based Services (continued) Finger
Remote Procedure Call (RPC)
Simple Network Management Protocol (SNMP)
NetBIOS over TCP/IP
Slide 45 : Basic TCP/IP Services 45
Slide 46 : Basic TCP/IP Services 46
Decoding Application Layer Protocols : Basic TCP/IP Services 47 Decoding Application Layer Protocols Decoding TCP/IP Application layer traffic largely depends on two separate forms of analysis
Understanding specific service’s 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
Summary : Basic TCP/IP Services 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
Summary (continued) : Basic TCP/IP Services 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
Summary (continued) : Basic TCP/IP Services 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