Networked Applications. 2 There are many applications such as: Web-enabled database access Internet...

Networked Applications

2

Networked Applications

There are many applications such as: Web-enabled database access Internet E-mail IP telephony for voice-data convergence

Each is important

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Web-Enabled Database Access

Problem: Database is on a “database server”

Mainframe or client/server server These need proprietary client software or a

terminal

Problem: Most users only have browsers Solution: an application server (webserver

with intermediary software) mediates between the two

User with Browser Database ServerApplication Server

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Web-Enabled Database Access Step 1: User types URL of data entry form Step 2: Webserver application sends form

Step 3: User types information in form, hits Send Browser puts data in a request line GET keyword /cgi-bin is the absolute path to a directory holding

an intermediary program, bogo.exe Data separated from absolute path by ? last field contains the value Lee first field contains the value Pat

User with Browser Database Server

URL

FormApplication Server

GET /cgi-bin/bogo.exe?last=Lee&first=Pat

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Step 3: Application server webserver software passes data form to the intermediary program, Bogo.exe, on the webserver

Application Server

WebserverApplicationSoftware

IntermediaryProgram

(Bogo.exe)

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Step 4: Bogo.exe puts the data into a query in the database server’s standard format Sends the query to the server


StandardQuery

Application Server

(Bogo.exe)

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Step 5: Database server sends response in its standard format to the intermediary program, Bogo.exe


StandardResponse

Application Server

(Bogo.exe)

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Web-Enabled Database Access Step 6: Application server

intermediary software (Bogo.exe) creates a new HTML webpage containing the response

Application Server

IntermediaryProgram

(Bogo.exe)

WebpageWebpage

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Step 7: Application server intermediary software passes this webpage to the webserver application program

Step 8: Webserver application program passes the webpage to the browser

Application Server

WebserverApplicationSoftware

IntermediaryProgram

(Bogo.exe)

WebpageWebpage

User with Browser

WebpageWebpage

Application Server

Step7 Step8

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Transparency Browser does not know that it is dealing with a

database server; it sends standard webserver commands, gets webpages back

Database server does not know it is dealing with a browser; receives standard database server requests, sends standard database server responses

No changes are needed in the browser or database application software; process is transparent to both the browser and the database server

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Web-Enabled Database Access CGI and Other Programs

Intermediary program (Bogo.exe) does the actual translation work

Webserver application programs have a standardized way of moving data to and from other programs

Common Gateway Interface (CGI) standard

WebserverApplication

Program


Program

IntermediaryProgram

(Bogo.exe)

IntermediaryProgram

(Bogo.exe)

DatabaseApplication

Program

DatabaseApplication

ProgramCGI

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CGI Starts a new copy of the intermediary

program every time the intermediary program is called

This is very slow OK only for small applications


Program


Program

IntermediaryProgram

(Bogo.exe)

IntermediaryProgram

(Bogo.exe)

DatabaseApplication

Program

DatabaseApplication

Program

CGI IntermediaryProgram

(Bogo.exe)

IntermediaryProgram

(Bogo.exe)

IntermediaryProgram

(Bogo.exe)

IntermediaryProgram

(Bogo.exe)

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Application Program Interfaces (APIs) Database servers have proprietary ways of

communication with other application programs

Other application program sends an application program interface (API) call to the database program

Faster than CGI but proprietary

Webserver applications do not support all database APIs


Program


Program

DatabaseApplication

Program

DatabaseApplication

Program

API

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Web-Enabled Database Access Client-Side Processing

Webserver can download webpage with Java or Active-X program

Client can then communicate directly with the database server


Webpage withJava applet

Subsequent Interactions

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Mainframes

Contain about 70% of corporate data from operations (accounting, payroll, billing, etc.)

Often the “database server” in web-enabled database applications

Dominated by IBM

Mainframe competitors build clones Called plug-compatible machines

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Terminal-Host Communication Traditionally, Just a Terminal, Host, and

Transmission Line Poor response time Poor user interface: sending graphics over a

distance is expensive (and lines usually are slow)

Inadequate for production workers who use their terminals hours per day

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Mainframe Communication

User site has multiple terminal users 3270 Terminals

High speeds, some color, some graphics

UserSite

3270 Terminal

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Mainframe Communication Cluster Controller at User Site

Supports a cluster of terminals and printers

Provides limited on-screen text editing power to terminals

This elimination of text editing work allows the mainframe to focus on high-value database chores

ClusterController

LimitedText Editing

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Mainframe Communication Cluster Controller at User Site

Supports a cluster of terminals and printers

Provides limited on-screen text editing power to terminals

This also reduces response time because editing is done locally

ClusterController

LimitedText Editing

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Cluster Controller at User Site Multiplexes transmissions of multiple

terminals and printers to the central site This reduces transmission costs, which

are expensive for higher-speed long-distance links

CentralSite

CentralSiteLong-

DistanceLine

A A A A AA A

BB

B B

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Mainframe Communication Transmission Line

Long-distance lines are expensive per bit sent

But 3270 terminals need high speeds Multiplexes terminal communication onto

56 kbps, 1.544 Mbps or faster line to give high speed but keep cost reasonable

CentralSite

CentralSiteLong-

DistanceLine

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Mainframe Communication Central Site Communications Controller

Handles multiplexing to reduce transmission cost

Handles detailed interactions with cluster controllers, freeing mainframe to deal with database processing

CommunicationsController

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Mainframe Communication Mainframe

Handles high-value database work Must be freed of low-value

communications processing work to be economically efficient

Mainframe

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Reducing Response Time Text editing work is done locally Still delay for heavy database work on

mainframe

Reducing Transmission Costs Multiplexing, and

Cluster controller provides limited local screen editing, so fewer bits need to be transmitted to and from the mainframe

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Reducing Work the Mainframe Needs to Do, so that it can Focus on High-Value Database Processing Cluster controller handles most text-

editing chores freeing mainframe from having to support this work, and

Communications controller handles details of communication with cluster controllers, freeing mainframe from having to support this work

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Application Servers

NOT Part of Mainframe Communications Can act as terminals or cluster controllers

Transparent to mainframe: no need to do anything differently on mainframe system

App Server

App Server

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Mainframes Use SNA Standards Architecture

Instead of TCP/IP Not peer-to-peer control; Master-slave

control under a System Services Control Point program on a mainframe

SSCP program governs all sessions among devices

SSCP

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Mainframes

SNA Standards Architecture Like TCP/IP and OSI, uses layering

Uses OSI standards at the physical and data link layers

SNA Path Control layer is like TCP/IP internet layer and OSI network layer

SNA Transmission Control layer is like the OSI and TCP/IP transport layer

However, not peer to peer operation; master-slave operation under the control of the SSCP

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Mainframes

SNA Standards Architecture Highest layers are like OSI layers

Network Addressable Unit (NAU) Services layer is like OSI session layer

Data Flow Control layer is like OSI presentation layer

However, applications are not standardized within SNA

There is no SNA application layer

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Mainframes

SNA NAUs Communication takes place between

network addressable units (NAUs) Unit is a general name for a

communicating entity In networks, communicating entities must

have addresses; So they are network addressable units

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Mainframes Logical Units

Deal directly with end users Terminals are logical units!

Connection points on mainframe (not mainframe itself) deal with application programs,which are considered to be end users

LU6Connection

Application

HumanUser

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Mainframes

Physical Units Do not deal directly with end users Mainframe, communications controller,

cluster controller Path control network connects cluster

controller and communication controller

PathControlNetwork

PathControlNetwork

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Mainframes

SSCP Third type of NAU Program located on the mainframe In classic SNA, two other NAUs can only

be connected under the control of the SSCP

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Mainframes SSCP

Third type of NAU Program located on the mainframe In classic SNA, two other NAUs can only be connected under

the control of the SSCP

Versions of SNA Classic SNA

All communication under the control of SSCP

Advanced Peer-to-Peer Networking (APPN) Newer; NAUs can connect directly

High-Performance Routing Classic SNA and APPN are difficult to route Newer still; HPR improves routing

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Mainframes

SNA and Router Networks To link cluster controllers to

communications controller over routed networks

Data Link Switching (DLSw) standard supports SNA transmission through routers

High-Performance Routing (HPR) is better

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Mainframes Mainframes and TCP/IP Networks

TN3270E TN3270E servers communicate with

mainframe Users have PCs with TN3270E client

software that emulates 3270 terminals

TCP/IPNetwork

TCP/IPNetwork

PC withTN3270E

Client

TN3270E Server

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Electronic Mail

Client Software and Mail Hosts Client PC has E-Mail client software that

communicates with user’s mail host Mail hosts deliver outgoing mail to other

mail hosts

PC withE-Mail Client Mail Host Mail Host

PC withE-Mail Client

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SMTP

Simple Mail Transfer Protocol (SMTP) Standard for mail host-mail host

exchanges E-Mail Client often sends messages to

mail host via SMTP, but not always

PC withE-Mail Client Mail Host Mail Host

SMTP SMTP

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SMTP Operation For Each Message, the Sending

Process Makes a connection Gives name of sender (From) and gets OK Gives names of receivers individually and

gets OK for each separately Asks to send message, gets OK Sends message, gets confirmation Closes connection

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Receiving and Sending E-Mail

User’s Mail Host Stores Incoming Files in the User’s Mailbox User later retrieves them User also sends outgoing mail

Client PC Mail HostWith User’s Mailbox

Receive Mail

Send Mail

41File Server Program Access E-Mail

Use proprietary ways to send messages, get messages, and in other ways interact with the mail host Can be used only on LANs Cannot be used over the Internet

LAN

PC with FSPAE-Mail Program

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POP Clients

POP (Post Office Protocol) is the most popular standard for mail downloading Download messages all or selectively Send outgoing messages via SMTP Works via Internet

PC withInternet E-Mail Client Mail Host Mail Host

SMTP SMTP

POP

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POP Operation Several client-mail host interactions

needed to download new mail Log into mail host Can ask how many new messages there are

and how long they are Can download all or download one at a time If download one at a time, can decide based

on length Can delete messages on host after

downloading Close the session

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IMAP Clients IMAP (Internet Message Access

Protocol) But not as widely supported as POP Send outgoing messages via SMTP Works via the Internet More sophisticated than POP

Can do more on mail server’s mailbox than download and delete messages; can fully manage the mailbox

PC withInternet E-Mail Client Mail Host Mail Host

SMTP SMTP

IMAP

45Browser Clients (Web-Based E-Mail) Client is Browser Mail Host is a Webserver

Mail host sends HTML pages to client User types messages and retrieval data in

forms, sends back All communication is via HTTP

PC withBrowser

WebserverMail Host

Mail Host

HTTP SMTP

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Telnet Clients Some mail hosts support Telnet Telnet client on PC emulates a simple

terminal No color or graphics Monospaced Text Sometimes only way to interact with a

mail host

PC withTelnet Client

Mail HostSupporting Telnet

Mail Host

Telnet SMTP

47Recap on Internet E-Mail Transmission

Communication Between Mail Hosts SMTP

Communication From Client to its Mail Host SMTP Proprietary file server program access on

LANs HTTP Telnet

48Recap on Internet E-Mail Transmission

Communication to Client from its Mail Host to deliver messages POP or IMAP Proprietary file server program access on

LANs HTTP Telnet

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Message Structure Standards

RFC 822 Text-only message bodies

MIME Multimedia message bodies and headers Not widely used for bodies or headers

HTML Bodies Becoming common Not well standardized; Limited

interoperability between mail clients

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Attachments

Send a message Attach a file (word processing document,

spreadsheet, graphic, etc.) E-mail can be a file delivery mechanism

Viruses Attachments may contain viruses

Even messages without attachments may contain viruses today

Virus scanning before opening is critical

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Attachments Problem

Attached files use all 8 bits of each byte Called binary data

On Internet, can only use the first seven bits

Called 7-bit ASCII In Internet transmission, 7th bit may be

truncated if send binary file

1010101010101010

Binary

x1010101x1010101

Internet

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Attachments Internet Encoding

Files must be Internet encoded before transmission to travel over the Internet using only the first 7 bits in each byte

At the receiving end, files must be Internet decoded so that applications can read them

1010101010101010

Binary

x1010101x1010101

Internet

x1010101x1010101

Internet

1010101010101010

Binary

InternetEncoding

InternetTransmission

InternetDecoding

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Attachments

Internet Encoding Standards Communicating mail clients must use the

same Internet encoding standard to encode and decode

MIME Several versions of MIME exist Basic MIME is almost universally

supported by e-mail clients today Binhex is commonly used on Macintoshes UUENCODE is common in UNIX

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Attachments

E-Mail users should negotiate before sending an attachment Internet encoding standard they will use Application file format they will use

If same application program and version, fine

If same application program and different versions, send in format of older version

If different application programs, send in a format and version the other can import

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E-Mail Standards Recap

Transmission Standards Sending messages (SMTP, etc.) Receiving messages (POP, IMAP, etc.)

Message Structure Standards Message header and body (RFC 822, MIME,

HTML) Attachments: common Internet encoding

standard Attachments: common application file

format

56IP Telephony

Voice-Data Convergence

What is IP Telephony? Transmit telephone conversations in IP packets

sent over the Internet or another network, such as Ethernet, Frame Relay, or ATM carrying IP packets

Digitize the outgoing voice signal Packetize (place in packets) and send over IP

packet-switched networks Reverse at other end

IP Packet

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Why IP Telephony? Save Money Digitizing Voice More Efficiently

Current telephone system also digitizes voice for internal digital communication within the telephone network

Current telephone system generates a stream of 64 kbps, then steals 8 kbps for signaling, leaving 56 kbps

This is a lot of bits to move per second on expensive long-distance and international lines

With newer technology, IP telephony digitizes voice to between 12 kbps and 16 kbps with good quality

Fewer bits to send means lower transmission cost

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Why IP Telephony?

Packet-Switched Network Delivery Traditional telephony is circuit-switched

Charged for 56 kbps channels whether use them or not

Packet switching multiplexes transmissions

Only pay for capacity actually used

Voice-Data Convergence Corporations now have separate networks for voice and

data

This is expensive in terms of staffing labor and technical charges

Voice-data convergence: use one network (IP) for both

Reduces staff and technical costs

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Why IP Telephony?

Save Money: Recap

Efficient digitization to send less than 8 kbps

Multiplexing on packet-switched networks Internet connection is already in place

Voice-data convergence reduces staff, other costs

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Problem of Latency Packet-Switched Networks Often Have

Latency (Delay) Latency is Bad for Voice Conversations

At latency of 200 milliseconds (ms), conversation is difficult because of turn-taking awkwardness

At latency of 500 ms, conversation is impossible

Variable latency from one packet to the next makes voice sound jittery (jitter)

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Reducing Latency

Problem is the Internet Backbone Often has high latency

ISPs Have Lower Latency Internally May offer service level agreements (SLAs)

for latency

SiteSite ISPISP InternetBackbone

InternetBackbone ISPISP SiteSite

OftenHigh Latency

UsuallyLow Latency

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Reducing Latency

Solution Connect all corporate sites to a single ISP

Possible because some ISPs have access points in many places around the country or even around the world

Connect all corporate sites to a single packet-switched PSDN

Packet-switched PSDNs also have low latency, SLAs

SiteSite ISP/ PSDNISP/ PSDN SiteSite

SLA forLow Latency

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IP Telephony Standards

Based on H.323 Videoconferencing Standard from ITU-T For videoconferencing over the Internet or

other IP networks

IETF, ITU-T have agreed to work together on IP telephony standards

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