CIS-325: Data Communications 1 CIS-325 Data Communications Dr. L. G. Williams, Instructor

CIS-325: Data CommunicationsCIS-325: Data Communications 11

CIS-325Data CommunicationsCIS-325Data Communications

Dr. L. G. Williams, InstructorDr. L. G. Williams, Instructor


Chapter ThirteenChapter Thirteen

Distributed ApplicationsDistributed Applications


Key Distributed ApplicationsKey Distributed Applications

Electronic MailElectronic Mail Electronic Data Interchange (EDI)Electronic Data Interchange (EDI) Web-Based ApplicationsWeb-Based Applications


Public E-MailPublic E-Mail

Public is provided by a vendor, generally Public is provided by a vendor, generally via a dial-up networkvia a dial-up network

Messages can be sent to any other Messages can be sent to any other registered userregistered user

Gateway required to send messages to users Gateway required to send messages to users outside the systemoutside the system

e.g. AOL, MCI Maile.g. AOL, MCI Mail


Private E-MailPrivate E-Mail

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

LAN environmentLAN environment Host examples: DEC All-In-One, IBM PROFSHost examples: DEC All-In-One, IBM PROFS LAN examples: CC:Mail, QuickMailLAN examples: CC:Mail, QuickMail

Owned and operated by an organization for Owned and operated by an organization for internal messaging requirements internal messaging requirements


Public vs. PrivatePublic vs. Private

Features and services can be quite similarFeatures and services can be quite similar Private systems involve higher initial cost, low or Private systems involve higher initial cost, low or

no transaction costsno transaction costs Public systems involve little initial cost, ongoing Public systems involve little initial cost, ongoing

transaction coststransaction costs Private e-mail offers better integration with Private e-mail offers better integration with

installed systemsinstalled systems Public systems offer wider range of delivery Public systems offer wider range of delivery

optionsoptions


Internet E-MailInternet E-Mail

Does not fit directly into either categoryDoes not fit directly into either category Transfer mechanism for exchanging mail Transfer mechanism for exchanging mail

among systems, rather than a mail system among systems, rather than a mail system itselfitself


Single System E-MailSingle System E-Mail

Only allows users of a shared system to Only allows users of a shared system to exchange messagesexchange messages

Each user has unique identifier and mailboxEach user has unique identifier and mailbox Sending a message simply puts it into Sending a message simply puts it into

recipients’ boxrecipients’ box Recipient fetches or reads message when Recipient fetches or reads message when

desireddesired


Multiple Systems E-MailMultiple Systems E-Mail

Distributed system enables mail servers to Distributed system enables mail servers to connect over a network to exchange mailconnect over a network to exchange mail

Functions splitFunctions split User agent handles preparation, submission, User agent handles preparation, submission,

reading, filing, etcreading, filing, etc Transfer agent receives mail from user, determines Transfer agent receives mail from user, determines

routing, communicates with remote systemsrouting, communicates with remote systems Interconnection requires standardsInterconnection requires standards


Simple Mail Transfer Protocol (SMTP)Simple Mail Transfer Protocol (SMTP)

Standard for TCP/IP mail transfer, defined Standard for TCP/IP mail transfer, defined in in RFC 821RFC 821

Concerned addressing and delivery, not Concerned addressing and delivery, not content, with two exceptionscontent, with two exceptions Character set standardized as 7-bit ASCIICharacter set standardized as 7-bit ASCII Adds log information to message that indicates Adds log information to message that indicates

message pathmessage path


Basic E-Mail OperationBasic E-Mail Operation

User creates message with user agent User creates message with user agent programprogram Text includes RFC 822 header and body of Text includes RFC 822 header and body of

messagemessage List of destinations derived from headerList of destinations derived from header

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


SMTP Mail FlowSMTP Mail Flow

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

hostshosts

SMTP protocol attempts to provide error-free SMTP protocol attempts to provide error-free transmission, but does not provide end-to-end transmission, but does not provide end-to-end acknowledgementacknowledgement

SMTP receiver accepts messages, places it in mailbox or SMTP receiver accepts messages, places it in mailbox or forwardsforwards


Limitations of SMTP and RFC822Limitations of SMTP and RFC822

Cannot transmit executables or binary files without Cannot transmit executables or binary files without conversion into text through non-standard programs (e.g. conversion into text through non-standard programs (e.g. UUENCODE)UUENCODE)

Cannot transmit diacritical marksCannot transmit diacritical marks Transfers limited in sizeTransfers limited in size Gateways do not always map properly between EBCDIC Gateways do not always map properly between EBCDIC

and ASCIIand ASCII Cannot handle non-text data in X.400 messagesCannot handle non-text data in X.400 messages Not all SMTP implementations adhere completely to Not all SMTP implementations adhere completely to

RFC821 (tabs, truncation, etc)RFC821 (tabs, truncation, etc)


MIME (Multipurpose Internet Mail Extensions)MIME (Multipurpose Internet Mail Extensions)

Intended to resolve problems with SMTP Intended to resolve problems with SMTP and RFC822and RFC822

Specifies five new header fields, providing Specifies five new header fields, providing info about body of messageinfo about body of message

Defines multiple content formats Defines multiple content formats Defines encodings to enable conversion of Defines encodings to enable conversion of

any type of content into transferable formany type of content into transferable form


Electronic Data Interchange (EDI)Electronic Data Interchange (EDI)

Direct, computer-to-computer exchange of Direct, computer-to-computer exchange of business databusiness data

Replaces use of paper documents Replaces use of paper documents Requires two participants to agree on Requires two participants to agree on

electronic format for the dataelectronic format for the data Two parties within a company (depts)Two parties within a company (depts) Companies and customersCompanies and customers Multiple companiesMultiple companies


Benefits of EDIBenefits of EDI

Cost savingsCost savings SpeedSpeed Reduction of errorsReduction of errors SecuritySecurity Integration with office automationIntegration with office automation Just-in-time deliveryJust-in-time delivery


EDI Layered ArchitectureEDI Layered Architecture

Semantic Layer: describes the business Semantic Layer: describes the business application (e.g. procurement)application (e.g. procurement)

Standard Layer: X.12 from ANSI, EDIFCT Standard Layer: X.12 from ANSI, EDIFCT from UNfrom UN

Transport Layer: E-mail, Point to Point, Transport Layer: E-mail, Point to Point, WWWWWW

Physical Layer: Dial-up lines, Internet, Physical Layer: Dial-up lines, Internet, WANsWANs


EDI v E-MailEDI v E-Mail

EDIEDI Typically no human Typically no human

involvement in involvement in processing the processing the information; interface information; interface is software-to-softwareis software-to-software

E-MailE-Mail Data not necessarily Data not necessarily

structured for software structured for software processing. Human-to-processing. Human-to-software exchange is software exchange is usually involved on at usually involved on at least one end.least one end.


World Wide WebWorld Wide Web

Developed by Tim Berners-Lee in 1991 at Developed by Tim Berners-Lee in 1991 at the European Particle Physics Laboratory the European Particle Physics Laboratory (CERN) to allow physicists around the (CERN) to allow physicists around the world to share information world to share information

Marc Andreessen, employee at NCSA, Marc Andreessen, employee at NCSA, introduced the GUI Web browser, Mosaic, introduced the GUI Web browser, Mosaic, in 1993.in 1993.


World Wide Web TechnologyWorld Wide Web Technology

Based on the concept of hypertextBased on the concept of hypertext Single interface to a variety of protocols and Single interface to a variety of protocols and

standards to access the information on the Internetstandards to access the information on the Internet Has become the predominant Internet applicationHas become the predominant Internet application

1993: annual rate of growth is 341,634%1993: annual rate of growth is 341,634% 1995: surpassed all other applications in 1995: surpassed all other applications in

amount of data being transferredamount of data being transferred


World Wide Web DocumentsWorld Wide Web Documents

Documents have embedded selectable links Documents have embedded selectable links that point to other documentsthat point to other documents

Documents can be text or non-textual Documents can be text or non-textual information such as audio, video, or information such as audio, video, or multimedia documentsmultimedia documents

Multimedia nature of the web allows non-Multimedia nature of the web allows non-text information to be embedded into text information to be embedded into documents, not just linked separatelydocuments, not just linked separately


World Wide Web FunctionsWorld Wide Web Functions

Display HTML pagesDisplay HTML pages Retrieve files (often using FTP)Retrieve files (often using FTP) Access Gopher sitesAccess Gopher sites Read newsgroupsRead newsgroups Search for information or people Search for information or people Display still images and videoDisplay still images and video Listen to sound filesListen to sound files Activate telnet connectionsActivate telnet connections


World Wide Web OperationWorld Wide Web Operation

Data stored on serversData stored on servers Users access data with browsersUsers access data with browsers

GUI browser (e.g, Mosaic, Netscape, Internet GUI browser (e.g, Mosaic, Netscape, Internet Explorer, etc.) requires a direct Internet Explorer, etc.) requires a direct Internet connection (dial-up or LAN)connection (dial-up or LAN)

Browser requests access to a pageBrowser requests access to a page Server transfers copy of page to requestorServer transfers copy of page to requestor


Uniform Resource Locator (URL)Uniform Resource Locator (URL)

provide a standard provide a standard means of locating means of locating Internet documentsInternet documents

simple addressing simple addressing scheme unifies a wide scheme unifies a wide variety of disparate variety of disparate protocolsprotocols

specify the three pieces of specify the three pieces of informationinformation the protocol to be used (e.g., http, the protocol to be used (e.g., http,

ftp, gopher, telnet, etc.)ftp, gopher, telnet, etc.) the server (and optional port)the server (and optional port) the file path to retrievethe file path to retrieve e.g., e.g., http://www.rit.edu/~ellics/index.htmlhttp://www.rit.edu/~ellics/index.html

http://www.itcs.com:80/elawley/http://www.itcs.com:80/elawley/ftp://ftp.netscape.com/ftp://ftp.netscape.com/telnet://wally.rit.edu/telnet://wally.rit.edu/gopher://gopher.cni.org/gopher://gopher.cni.org/


HyperText Markup Language (HTML)HyperText Markup Language (HTML)

Derived from SGML (Standard Generalized Derived from SGML (Standard Generalized Markup Language)Markup Language)

Uses tags to indicate formatting characteristics Uses tags to indicate formatting characteristics them with a specific formatthem with a specific format

Tags are defined functionally, not visuallyTags are defined functionally, not visually Tags can indicate a link to another document or Tags can indicate a link to another document or

resourceresource Tagged text can be displayed by choosing “View Tagged text can be displayed by choosing “View

Source” in most browsersSource” in most browsers


HyperText Transfer Protocol (HTTP)HyperText Transfer Protocol (HTTP)

the primary protocol used to distribute the primary protocol used to distribute information within WWWinformation within WWW

a “connectionless” protocola “connectionless” protocol limited to one request per connectionlimited to one request per connection the connection is broken after each request the connection is broken after each request