Networked Applications

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

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 Application Server Database Server

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 URL GET /cgi-bin/bogo.exe?last=Lee&first=Pat Form User with Browser Application Server Database Server

Web-Enabled Database Access Step 3: Application server webserver software passes data form to the intermediary program, Bogo.exe, on the webserver Webserver Application Software Intermediary Program (Bogo.exe) Application Server

Web-Enabled Database Access Step 4: Bogo.exe puts the data into a query in the database server’s standard format Sends the query to the server (Bogo.exe) Standard Query Application Server User with Browser Database Server

Web-Enabled Database Access Step 5: Database server sends response in its standard format to the intermediary program, Bogo.exe (Bogo.exe) Standard Response User with Browser Application Server Database Server

Web-Enabled Database Access Step 6: Application server intermediary software (Bogo.exe) creates a new HTML webpage containing the response Intermediary Program (Bogo.exe) Webpage Application Server

Web-Enabled Database Access 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 Step8 Step7 Webpage Webpage Webserver Application Software Intermediary Program (Bogo.exe) User with Browser Application Server Application Server

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

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 Webserver Application Program Intermediary Program (Bogo.exe) Database Application Program CGI

Web-Enabled Database Access 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 Webserver Application Program Intermediary Program (Bogo.exe) Database Application Program Intermediary Program (Bogo.exe) CGI Intermediary Program (Bogo.exe)

Web-Enabled Database Access 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 Webserver Application Program Database Application Program API

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 with Java applet Subsequent Interactions User with Browser Database Server

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

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

Mainframe Communication User site has multiple terminal users 3270 Terminals High speeds, some color, some graphics User Site 3270 Terminal

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 Limited Text Editing Cluster Controller

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 Limited Text Editing Cluster Controller

Mainframe Communication 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 A A A A A A B B A Central Site Long- Distance Line B B

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 Central Site Long- Distance Line

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 Communications Controller

Mainframe Communication Handles high-value database work Must be freed of low-value communications processing work to be economically efficient Mainframe

Mainframe Communication 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

Mainframe Communication 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

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

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

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

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

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

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 Application Human User LU6 Connection

Mainframes Physical Units Do not deal directly with end users Mainframe, communications controller, cluster controller Path control network connects cluster controller and communication controller Path Control Network

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

Mainframes SSCP Versions of SNA Classic SNA 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

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

Mainframes Mainframes and TCP/IP Networks TN3270E TN3270E servers communicate with mainframe Users have PCs with TN3270E client software that emulates 3270 terminals TCP/IP Network PC with TN3270E Client TN3270E Server

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 with E-Mail Client PC with E-Mail Client Mail Host Mail Host

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 SMTP SMTP PC with E-Mail Client Mail Host Mail Host

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

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 Receive Mail Send Mail Client PC Mail Host With User’s Mailbox

File 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 PC with FSPA E-Mail Program LAN

Internet E-Mail Client 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 SMTP SMTP POP PC with Internet E-Mail Client Mail Host Mail Host

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

Internet E-Mail Client 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 SMTP SMTP IMAP PC with Internet E-Mail Client Mail Host Mail Host

Browser 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 HTTP SMTP PC with Browser Webserver Mail Host Mail Host

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 Telnet SMTP PC with Telnet Client Mail Host Supporting Telnet Mail Host

Recap on Internet E-Mail Transmission Communication Between Mail Hosts SMTP Communication From Client to its Mail Host Proprietary file server program access on LANs HTTP Telnet

Recap 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

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

Attachments Send a message Viruses 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

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 10101010 Binary x1010101 Internet

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 Internet Encoding Internet Transmission Internet Decoding 10101010 x1010101 Internet x1010101 Internet 10101010 Binary Binary

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

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

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

IP 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

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

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

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

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)

Reducing Latency Problem is the Internet Backbone Often has high latency ISPs Have Lower Latency Internally May offer service level agreements (SLAs) for latency Internet Backbone Site ISP ISP Site Usually Low Latency Often High Latency

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 ISP/ PSDN Site Site SLA for Low Latency

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