1. Chapter 16: Distributed Applications Business Data Communications, 4e

2. 2 Electronic Mail Features 8Message Preparation 8Word processing 8Annotation 8Message Sending 8User directory 8Timed delivery 8Multiple addressing 8Message priority 8Status information 8Interface to other facilities 8Message Receiving 8Mailbox scanning 8Message selection 8Message notification 8Message reply 8Message rerouting

3. Business Data Communications, 4e 3 Single System E-Mail 8Only allows users of a shared system to exchange messages 8Each user has unique identifier and mailbox 8Sending a message simply puts it into recipients’ box 8e.g. RITVAX, AOL

4. Business Data Communications, 4e 4 Multiple Systems E-Mail 8Distributed system enables mail servers to connect over a network to exchange mail 8Functions split 8User agent handles preparation, submission, reading, filing, etc 8Transfer agent receives mail from user, determines routing, communicates with remote systems 8Interconnection requires standards

5. Business Data Communications, 4e 5 Simple Mail Transfer Protocol (SMTP) 8Standard for TCP/IP mail transfer, defined in RFC 821RFC 821 8Concerned addressing and delivery, not content, with two exceptions 8Character set standardized as 7-bit ASCII 8Adds log information to message that indicates message path

6. Business Data Communications, 4e 6 Basic E-Mail Operation 8User creates message with user agent program 8Text includes RFC 822 header and body of message 8List of destinations derived from header 8Messages are queued and sent to SMTP sender program running on a host

7. Business Data Communications, 4e 7 SMTP Mail Flow 8SMTP server transmits messages to appropriate hosts via TCP 8Multiple messages to same host can be sent on one connection 8Errors handling necessary for faulty addresses and unreachable hosts 8SMTP protocol attempts to provide error-free transmission, but does not provide end-to-end acknowledgement 8SMTP receiver accepts messages, places it in mailbox or forwards

8. Business Data Communications, 4e 8 SMTP Connection Setup 8Sender opens TCP connection to receiver 8Receiver acknowledges connection with “220 Service Ready” or “421 Service Not Available” 8If connection is made, sender identifies itself with the “HELO” command 8Receiver accepts identification with “250 OK”

9. Business Data Communications, 4e 9 SMTP Mail Transfer 8MAIL command identifies originator, provides reverse path for error reporting 8RCPT commands identify recipient(s) for message 8Receiver has several positive or negative responses to RCPT 8Sender will not send message until it is sure at least one copy can be delivered 8DATA command transfers message

10. Business Data Communications, 4e 10 Sample SMTP Exchange 8S: MAILFROM: R: 250 OK 8S: RCPT TO: R: 250 OK 8S: RCPT TO: R: 550 No such user here 8S: DATA R: 354 Start mail input; end with. S: Blah blah blah…. S:…etc. etc. etc. S:. R: 250 OK

11. Business Data Communications, 4e 11 SMTP Connection Closing 8Sender sends a QUIT command to initiate TCP close operation 8Receiver sends a reply to the QUIT command, then initiates its own close

12. Business Data Communications, 4e 12 RFC 822 8Defines format for text messages via electronic mail 8Used by SMTP as accepted mail format 8Specifies both envelope and contents 8Includes a variety of headers that can be included in the message header lines

13. Business Data Communications, 4e 13 Limitations of SMTP and RFC822 8Cannot transmit executables or binary files without conversion into text through non-standard programs (e.g. UUENCODE) 8Cannot transmit diacritical marks 8Transfers limited in size 8Gateways do not always map properly between EBCDIC and ASCII 8Cannot handle non-text data in X.400 messages 8Not all SMTP implementations adhere completely to RFC821 (tabs, truncation, etc)

14. Business Data Communications, 4e 14 MIME (Multipurpose Internet Mail Extensions) 8Intended to resolve problems with SMTP and RFC822 8Specifies five new header fields, providing info about body of message 8Defines multiple content formats 8Defines encodings to enable conversion of any type of content into transferable form

15. Business Data Communications, 4e 15 MIME Header Fields 8MIME-Version: Indicates compliance with RFCs 1521 and 1522 8Content-Type: Describes data in sufficient detail for receiver to pick method for representation 8Content-Transfer-Encoding: Indicates type of transformation used to represent content 8Content-ID: Used to uniquely identify MIME entities 8Content-Description: Plain text description for use when object is not readable

16. Business Data Communications, 4e 16 MIME Content Types 8Seven major types: Text, Multipart, Message, Image, Video, Audio, Application 8Fourteen subtypes: See page 384 for details 8Text provides only plain subtype, but a richtext subtype is likely to be added 8Multipart indicates separate parts, such as text and an attachment 8MIME types are used by web servers, as well

17. Business Data Communications, 4e 17 Electronic Data Interchange (EDI) 8Direct, computer-to-computer exchange of business data 8Replaces use of paper documents 8Requires two participants to agree on electronic format for the data 8Two departments within a company 8Companies and customers 8Multiple companies

18. Business Data Communications, 4e 18 Benefits of EDI 8Cost savings 8Speed 8Reduction of errors 8Security 8Integration with office automation 8Just-in-time delivery

19. Business Data Communications, 4e 19 EDI v E-Mail 8EDI 8Typically no human involvement in processing the information; interface is software-to-software 8E-Mail 8Data not necessarily structured for software processing. Human-to- software exchange is usually involved on at least one end

20. Business Data Communications, 4e 20 Components of EDI Systems 8Application 8Translation Software 8Communications Network

21. Business Data Communications, 4e 21 EDI/Internet Integration 8RFC 1767, issued in 1995 defines a method for packaging EDI transactions in a MIME envelope. 8Additional requirements have since emerged: 8Security issues such as EDI transaction integrity, privacy and non-repudiation 8Support for exchanges by point-to-point, FTP, and SMTP protocols. 8An IETF working group is currently addressing these unresolved issues.

22. Business Data Communications, 4e 22 Enterprise Application Integration (EAI) 8linking applications, whether purchased or developed in-house, so they can better support a business process. 8Critical for implementation of Internet-based business strategies

23. Business Data Communications, 4e 23 EAI Illustrated