Download Networked Applications

Networked Applications
2
Networked Applications

There are many applications such as:



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Web-enabled database access
Internet E-mail
IP telephony for voice-data convergence
Each is important
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Web-Enabled Database Access
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Problem: Database is on a “database server”



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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
URL
 Data separated from absolute path by ?
 last field contains the value Lee
 first field contains the value Pat
GET /cgi-bin/bogo.exe?last=Lee&first=Pat
User with Browser
Form
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
User with Browser
Application Server
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
Webpage
Application Server
Intermediary
Program
(Bogo.exe)
9
Web-Enabled Database Access


Step7
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
Webpage
Webserver
Application
Software
Webpage
Intermediary
Program
(Bogo.exe)
Application Server
User with Browser
Application Server
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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
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

Webserver
Application
Program
Common Gateway Interface (CGI) standard
CGI
Intermediary
Program
(Bogo.exe)
Database
Application
Program
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
CGI
Intermediary
Intermediary
Program
Intermediary
Program
(Bogo.exe)
Program
(Bogo.exe)
(Bogo.exe)
Database
Application
Program
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
API
Database
Application
Program
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
User with Browser
Subsequent Interactions
Database Server
15
Mainframes

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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
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Called plug-compatible machines
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Terminal-Host Communication
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Traditionally, Just a Terminal, Host, and
Transmission Line


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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
User
Site
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
Limited
Text Editing
Cluster
Controller
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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
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
B
AAA B B
B
LongDistance
Line
A
Central
Site
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, 1.544 Mbps or faster line to give high
speed but keep cost reasonable
LongDistance
Line
Central
Site
22
Mainframe Communication


Central Site
Communications Controller

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Handles multiplexing to reduce transmission
cost
Handles detailed interactions with cluster
controllers, freeing mainframe to deal with
database processing
Communications
Controller
23
Mainframe Communication
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Mainframe

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Handles high-value database work
Must be freed of low-value communications
processing work to be economically efficient
Mainframe
24
Mainframe Communication
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Reducing Response Time

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Text editing work is done locally
Still delay for heavy database work on
mainframe
Reducing Transmission Costs

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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
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Application Servers
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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
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SNA Standards Architecture
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Like TCP/IP and OSI, uses layering
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Uses OSI standards at the physical and data link layers
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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
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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
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However, applications are not standardized
within SNA
 There is no SNA application layer
30
Mainframes
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SNA NAUs
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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
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Logical Units
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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
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Physical Units
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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
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SSCP
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Third type of NAU
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Program located on the mainframe
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In classic SNA, two other NAUs can only be
connected under the control of the SSCP
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Mainframes
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SSCP
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Third type of NAU
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Program located on the mainframe
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In classic SNA, two other NAUs can only be connected under
the control of the SSCP

Versions of SNA
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Classic SNA
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Advanced Peer-to-Peer Networking (APPN)
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All communication under the control of SSCP
Newer; NAUs can connect directly
High-Performance Routing
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Classic SNA and APPN are difficult to route
Newer still; HPR improves routing
35
Mainframes
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SNA and Router Networks

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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
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Mainframes and TCP/IP Networks
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TN3270E


PC with
TN3270E
Client
TN3270E servers communicate with mainframe
Users have PCs with TN3270E client software
that emulates 3270 terminals
TCP/IP
Network
TN3270E Server
37
Electronic Mail
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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
Mail Host
Mail Host
PC with
E-Mail Client
38
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
PC with
E-Mail Client
SMTP
Mail Host
Mail Host
39
SMTP Operation
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For Each Message, the Sending Process
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Makes a connection
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Gives name of sender (From) and gets OK
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Gives names of receivers individually and gets
OK for each separately
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Asks to send message, gets OK
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Sends message, gets confirmation
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Closes connection
40
Receiving and Sending E-Mail
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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
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Can be used only on LANs

Cannot be used over the Internet
PC with FSPA
E-Mail Program
LAN
42
POP Clients

POP (Post Office Protocol) is the most
popular standard for mail downloading

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
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
43
POP Operation
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Several client-mail host interactions needed
to download new mail



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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
IMAP Clients
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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

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
Can do more on mail server’s mailbox than download
and delete messages; can fully manage the mailbox
SMTP
PC with
Internet E-Mail Client
SMTP
IMAP
Mail Host
Mail Host
45
Browser Clients (Web-Based E-Mail)
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Client is Browser
Mail Host is a Webserver
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
Mail host sends HTML pages to client
User types messages and retrieval data in
forms, sends back
All communication is via HTTP
HTTP
PC with
Browser
SMTP
Webserver
Mail Host
Mail Host
46
Telnet Clients

Some mail hosts support Telnet

Telnet client on PC emulates a simple
terminal
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No color or graphics
Monospaced Text
Sometimes only way to interact with a mail host
Telnet
PC with
Telnet Client
SMTP
Mail Host
Supporting Telnet
Mail Host
47
Recap on Internet E-Mail Transmission
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Communication Between Mail Hosts
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SMTP
Communication From Client to its Mail Host

SMTP
Proprietary file server program access on LANs
HTTP
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Telnet
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48
Recap on Internet E-Mail Transmission
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Communication to Client from its Mail Host
to deliver messages
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POP or IMAP
Proprietary file server program access on LANs
HTTP
Telnet
49
Message Structure Standards
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RFC 822

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MIME

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Text-only message bodies
Multimedia message bodies and headers
Not widely used for bodies or headers
HTML Bodies

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Becoming common
Not well standardized; Limited interoperability
between mail clients
50
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
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
th bit may be
 In Internet transmission, 7
truncated if send binary file
10101010
x1010101
Binary
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
10101010
x1010101
x1010101
10101010
Binary
Internet
Internet
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 e-mail 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
IP Telephony
Voice-Data Convergence

56
What is IP Telephony?
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


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 packetswitched 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
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
58
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


ISPs Have Lower Latency Internally

Site
Often has high latency
May offer service level agreements (SLAs) for
latency
ISP
Internet
Backbone
Usually
Low Latency
Often
High Latency
ISP
Site
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

Packet-switched PSDNs also have low latency, SLAs
Site
PSDN
ISP/ PSDN
SLA for
Low Latency
Site
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