Transcript MIS 430 - Indiana State University

MIS 430
PART TWO: Network Fundamentals
Chapter 2
Application Layer
Chapter 2
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Tech Focus 2-1
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Servers
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Mainframe: 1,000s of users $million+
Minicomputer: 100s of users $50k-400K
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Sometimes DB servers in client-server nets
Microcomputer: 1 to many users, up to $30+K
Cluster: group of computers linked together to act
as one computer
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Shared resources
Load balanced
Scalable
Chapter 2
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Tech Focus 2-1, contd
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Clients
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Microcomputer: most common
Terminal: I/O only
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Dumb: no processing of data; just KB and display
Intelligent: adds local processing, storage, printer
Workstation: CAD and technical modeling
Network computer: Java, no hard disk; limited
Transaction Terminal: specialized device like ATM,
POS scanner, card swipe machine. Specific task.
Handheld – PDA or wearable (Xybernaut)
Chapter 2
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I. Application Architecture
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Way functions of the applications layer
are spread among servers and clients
Work functions of an application
program
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Data Storage DS
Data Access Logic DAL: work required to
access data such as SQL queries
Application Logic AL (aka business logic)
Presentation Logic PL: formatting info to
the user and accepting user commands
Chapter 2
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Host-Based Architecture
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First developed in 1960s; see Fig 2-1
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Server (host) does PL, AL, DAL, and DS
Client is a terminal (or PC running terminal
emulation SW)
Tight controls possible
Problems: cost is high, response can be
slow, and scalability only comes in large
chunks (e.g., like a mainframe)
Chapter 2
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Client-Based Architecture
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LANs appeared in late 1980s; fig 2-2
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Server: DS (e.g., MISNT or Befac)
Client: PL, AL, DAL
PC-based SW is plentiful, easy to use
Problems: all data must travel from
server to client, not just selected items,
and controls are weak; more network
traffic
Chapter 2
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Client-Server Architecture
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Very common today; see fig 2-3
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Server: DAL, DS
Client: PL, AL
Server maintains the data and
applications run on the client.
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If you run out of capacity, get a new client
Server adjudicates requests for data
Banner is an example of this at ISU
Chapter 2
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Client-Server, contd.
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Some application logic can be on server
Middleware: sits between server and
client
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Interprets and translates data
Manages message transfers (specific SW)
Allows multiple vendors to be involved
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EX: CORBA, ODBC (Open Data Base
Connectivity) to link computers
Chapter 2
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3-Tier Client Server
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Adds a 3rd application server in the
middle as in fig 2-4
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Database server: DAL, DL
Applications server: AL (middle)
Client: PL
EX: DB server is mainframe holding
data, AL server is a minicomputer
running an app, and client is a PC
Chapter 2
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N-tier Client Server
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Adds specialized servers; see fig 2-5
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DB server: DAL , DS
Application server: AL
Web server: AL
Client: PL
Requires a lot more network
communications between servers
More difficult to program and test
Chapter 2
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Clients in Client-Server
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Determines how much application logic
is on the client end
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Thin client: little or no application logic –
AL resides on the server
Fat (thick) client: all or most AL on client
Thin clients are the way of the future
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ASP (application service provider)
Access via browser and Java applets
Distributed computing model
Chapter 2
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Which Architecture?
Host
Based
Client
Based
Client
Server
Infrastructure High
$
Medium
Low*
Development
$
Low*
Medium
High
Scalability
Low
Medium
High*
Chapter 2
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II. World Wide Web
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History:
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CERN 1989 (hypertext concept) Angels and
Demons?
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Mosaic browser 1993 (U. Ill, Mark Andreessen
thesis)
Netscape 1994 (left U. Ill to form this company)
Microsoft 1996 Internet Explorer
Others: Opera, Lynx (text), Web TV; embedded in
printers, wireless routers, print servers, etc. Palm
Tungsten C (mine!)
Chapter 2
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How the Web Works
Example of 2-tier architecture
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Client needs browser (appl layer SW)
Server needs web server (IIS or Apache SW)
Process
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User types URL: protocol, server, and file name
Browser sends HTTP request (request line,
header, body); fig 2-9
Server returns HTTP response (status, header,
body); fig 2-10
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Status 200 means OK, 404 means Not Found
http://misnt.indstate.edu/bruce/ is not found
http://www.rexswain.com/httpview.html is a viewer of
response from the web server – cool!
Chapter 2
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Web Identifying Information
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This information about you appears
whenever you request a web site
Your IP address
 Browser and version
 Date and time
 Referrer URL
 Destination URL
http://www.howstuffworks.com/webserver.htm
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Chapter 2
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E-mail
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The most heavily used Internet application!
Advantages over regular mail
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Speed: seconds to a minute
Price: essentially free vs. $5+ for a letter or $15+ for
overnight
Attachments are machine readable: MIME encoding
Send to multiple recipients at the same time
Disadvantages
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Tacky: some don’t think it is “professional”
If one doesn’t check mail, it didn’t arrive!
Tasks longer to type than talk (but voice recognition)
Flame mail!
Easy to send something to the wrong person
Chapter 2
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How E-mail Works
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www.howstuffworks.com/email.htm cool!
Outgoing mail
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SMTP: Simple Mail Transport Protocol
Email client sends packet to SMTP server
Server reads destination and routes packets
Destination mail server puts in right mailbox
Incoming mail
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POP: Post Office Protocol
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Client requests message to be transferred to mail folders
(probably on hard drive)
IMAP: Internet Message Access Protocol
(GroupWise)
Chapter 2
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E-mail Headers (Underneath)
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Chapter 2
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3-Tier E-mail
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Use browser to get mail; see fig 2-12
Replace email client with web browser
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Load mail web page
Request/send email
Browser sends HTTP request to middle tier
web server
Web server requests info from email server
Process reverses, mail sent as HTML file
Chapter 2
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ISU E-mail Mess!
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Eudora, Outlook Express, Netscape Messenger e-mail
clients
HTML mail (Hotmail, Yahoo, Juno, etc)
Portal (http://myisu.indstate.edu)
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GroupWise (mail,calendar,tasks,shared data)
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[email protected] is primary student email
Username@citrine went away
Groupwise Client (full featured, fast)
WebAccess client (convenient, slow, few features)
Portal client => to GroupWise (compromise)
Groupware: Outlook (Exchange), Lotus Notes
Sept 1: Befac, Root, Scifac servers disappear!
Chapter 2
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Discussion Groups
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E-mail based
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Subscribe to discussion group
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Send mail to group
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To: [email protected]
Subscribe mis430-L firstname lastname
To: [email protected]
Redirected to all members of list
Archive history is optional to follow threads
Caution! Reply defaults to everyone in group
Hint: may need to turn off HTML e-mail &
signature because of extra words that are
misinterpreted as commands
Chapter 2
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Discussion Group Commands
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Each list processor is different, but
many use common commands to
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Get information on commands (help)
Join/leave (subscribe and unsubscribe)
See who is a member of a list
See class handout for Listproc
commands at ISU
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http://web.indstate.edu/it/techsupp/docs/listproc.htm
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III. Other Applications
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FTP – File Transport Protocol
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FTP:// is similar to HTTP:// protocol
FTP client sends request to FTP server
WS_FTP, CuteFTP GUI clients
Anonymous FTP vs. closed FTP (with
authentication)
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SDSNT and hackers: anonymous FTP allowed
initially with write access – ugh!
Chapter 2
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Other Applications, contd.
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Telnet: log on as terminal over the Internet
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Much less popular for end users now – more go
through web pages
Experts can connect to router or switch to
program it
Instant Messenger: AOL and MSN
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3-tier system: your client sends message to
IM server that redirects it to another IM client
Microsoft has its own new Live Communications
Server system - is IM a legitimate corporate tool?
Chapter 2
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Other Applications
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Videoconferencing (fig. 2.14)
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Webcasting
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One-way videoconferencing
RealPlayer and MS Media Viewer popular
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WebEx http://webex.com/ for demo
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Real-time audio and video over Internet
MS NetMeeting is popular
H.320 and H.323 protocols
Bandwidth is key for both!
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28.8k, 56k, 128k, 300k, faster
Chapter 2
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Mgt Focus 2-3: Alabama ADRS
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ADRS has 800 employees in AL serving
patrons all over the state
Uses IP H.323 videoconferencing to
save travel costs
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Ex: Weekly 90-minute meeting attended by
videoconference instead of driving 100 mi.
IP saves money over previous ISDN dialup
connection
Chapter 2
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