1. Networked Applications

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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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)

13. 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

14. 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

15. 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

16. 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

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

18. 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

19. 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

20. 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

21. Mainframe Communication
Transmission Line
Long-distance lines are expensive per bit sent
But 3270 terminals need high speeds
Multiplexes terminal communication onto 56 kbps, Mbps or faster line to give high speed but keep cost reasonable
Central
Site
Long-
Distance
Line

22. 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

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

24. 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

25. 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

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. Electronic Mail Client Software and Mail Hosts
Client PC has client software that communicates with user’s mail host
Mail hosts deliver outgoing mail to other mail hosts
PC with
Client
PC with
Client
Mail Host
Mail Host

38. SMTP Simple Mail Transfer Protocol (SMTP)
Standard for mail host-mail host exchanges
Client often sends messages to mail host via SMTP, but not always
SMTP
SMTP
PC with
Client
Mail Host
Mail Host

39. 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

40. 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

41. 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
Program
LAN

42. 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 Client
Mail Host
Mail Host

43. 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

44. 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 Client
Mail Host
Mail Host

45. 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

46. 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

47. 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

48. 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

49. 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

50. Attachments Send a message Viruses
Attach a file (word processing document, spreadsheet, graphic, etc.)
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

51. 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
Binary x
Internet

52. 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 x
Internet x
Internet
Binary
Binary

53. 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 clients today
Binhex is commonly used on Macintoshes
UUENCODE is common in UNIX

54. 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

55. 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

56. 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

57. 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

58. 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

59. 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

60. 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)

61. 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

62. 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

63. 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