Distributed Applications

Digital Business Communications Distributed Applications Key Distributed Applications ] Electronic Mail ] Electronic Data Interchange (EDI) ] Groupw...
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Digital Business Communications

Distributed Applications

Key Distributed Applications ] Electronic Mail ] Electronic Data Interchange (EDI) ] Groupware

See Stallings chapter 16

Electronic Mail

Common features of email

] A widely used communication medium in its own right ] Also the basis for other business communication tools including EDI, news and some kinds of groupware

Taxonomy of Email

Public

Ownership Private

Single system

Multiple Systems

Architecture

] Message preparation - word processing, annotation ] Message sending - user directory, timed delivery. Multiple addressing, message priority, status information, interfaces to other facilities ] Message receiving - mailbox scanning, message selection, notification, reply, forwarding

Public E-Mail ] Public is provided by a vendor, generally via a dial-up network ] Messages can be sent to any other registered user ] Gateway required to send messages to users outside the system ] e.g. AOL, Compuserve

Private E-Mail

Public v Private

] Integrated with the user’s computer system ] Can run on a central host, or as part of a LAN environment

] Features and services can be quite similar ] Private systems involve higher initial cost, low or no transaction costs ] Public systems involve little initial cost, ongoing transaction costs ] Private e-mail offers better integration with installed systems ] Public systems offer wider range of delivery options

\ Host examples: DEC All-In-One, IBM PROFS \ LAN examples: CC:Mail, QuickMail

] Owned and operated by an organization for internal messaging requirements

Internet E-Mail

Single System E-Mail

] Does not fit directly into either category ] More of a transfer mechanism for exchanging mail among systems, rather than a mail system itself

] Only allows users of a shared system to exchange messages ] Each user has unique identifier and mailbox ] Sending a message simply puts it into recipients’ box

Multiple Systems E-Mail ] Distributed system enables mail servers to connect over a network to exchange mail ] Functions split \ User agent handles preparation, submission, reading, filing, etc \ Transfer agent receives mail from user, determines routing, communicates with remote systems

] Interconnection requires standards

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

Basic E-Mail Operation

SMTP Mail Flow

] User creates message with user agent program \ Text includes RFC 822 header and body of message \ List of destinations derived from header

] Messages are queued and sent to SMTP sender program running on a host

Message header Message body List of destinations User Agent

SMTP sender

TCP to port 25 on SMTP receiver

Message Queue SMTP receiver

] SMTP server transmits messages to appropriate hosts via TCP \ Multiple messages to same host can be sent on one connection \ Errors handling necessary for faulty addresses and unreachable hosts

] SMTP protocol attempts to provide error-free transmission, but does not provide end-to-end acknowledgement ] SMTP receiver accepts messages, places it in mailbox or forwards

RFC 822 ] Defines format for text messages ] Used by SMTP as accepted mail format ] Specifies both envelope and contents ] Defines a variety of headers

Envelope Contents Header Body Nested message

User Mailboxes

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

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

MIME Header Fields

MIME Content Types

] MIME-Version: Indicates compliance with RFCs 1521 and 1522 ] Content-Type: Describes data in sufficient detail for receiver to pick method for representation ] Content-Transfer-Encoding: Indicates type of transformation used to represent content ] Content-ID: Used to uniquely identify MIME entities ] Content-Description: Plain text description for use when object is not readable

] Seven major types: Text, Multipart, Message, Image, Video, Audio, Application ] Fourteen subtypes: See Stallings page 384 for details ] Text provides only plain subtype, but a richtext subtype is likely to be added ] Multipart indicates separate parts, such as text and an attachment ] MIME types are used by web servers, as well

Electronic Data Interchange (EDI) ] Direct, computer-to-computer exchange of business data ] Replaces use of paper documents ] Requires two participants to agree on electronic format for the data \ Two parties within a company (depts) \ Companies and customers \ Multiple companies

EDI Layered Architecture Semantic Layer: describes the business application (e.g. procurement) Standard Layer: X.12 from ANSI, EDIFCT from UN Transport Layer: E-mail, Point to Point, WWW

Physical Layer: Dial-up lines, Internet, WANs

Benefits of EDI ] ] ] ] ] ]

Cost savings Speed Reduction of errors Security Integration with office automation Just-in-time delivery

Example application and transaction sets General Business Application Payment order/remittance advice Planning schedule Price sales catalogue Request for quotation Response to RFQ Inventory advice Purchase order Purchase order acknowledgement Ship notice Purchase order change request Purchase order change request acknowledgement Receiving advice Product transfer and resale

Example transaction set EDI Form 820: Payment order/remittance advice Transaction set header

M

1

Beginning segment

M

1

Currency Date/time Name Geographic location Administrative contact ... Transaction set trailer

O M O O O

1 10 1 1 3

Indicate start of form and assign control number Indicate total amount and enable automated transfer Currency to be used Pertinent dates Name of party Location of party Names of contact people

M

1

End of form/segment count

The uptake of EDI ] 1994 study reported that \ 42% of responding firms used EDI \ 100% of responding firms with < 250 employees were non-users

] Nearly 70% of EDI systems are initiated by customer (a hub) who demands that suppliers (the spokes) use EDI ] Small businesses coerced into adopting EDI to keep a valued customer

EDI v E-Mail ] EDI \ Typically no human involvement in processing the information; interface is softwareto-software

] E-Mail \ Data not necessarily structured for software processing. Human-to-software exchange is usually involved on at least one end.

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