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Chapter 2 1
MIS 430PART TWO: Network Fundamentals
Chapter 2Application Layer
Chapter 2 2
Tech Focus 2-1 Servers
Mainframe: 1,000s of users $million+ Minicomputer: 100s of users $50k-400K
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 Shared resources Load balanced Scalable
Chapter 2 3
Tech Focus 2-1, contd Clients
Microcomputer: most common Terminal: I/O only
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 4
I. Application Architecture Way functions of the applications layer
are spread among servers and clients Work functions of an application
program 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 5
Host-Based Architecture First developed in 1960s; see Fig 2-1
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 6
Client-Based Architecture LANs appeared in late 1980s; fig 2-2
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 7
Client-Server Architecture Very common today; see fig 2-3
Server: DAL, DS Client: PL, AL
Server maintains the data and applications run on the client. 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 8
Client-Server, contd. Some application logic can be on server Middleware: sits between server and
client Interprets and translates data Manages message transfers (specific SW) Allows multiple vendors to be involved
EX: CORBA, ODBC (Open Data Base Connectivity) to link computers
Chapter 2 9
3-Tier Client Server Adds a 3rd application server in the
middle as in fig 2-4 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 10
N-tier Client Server Adds specialized servers; see fig 2-5
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 11
Clients in Client-Server Determines how much application logic
is on the client end 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 ASP (application service provider) Access via browser and Java applets Distributed computing model
Chapter 2 12
Which Architecture?Host Based
Client Based
Client Server
Infrastructure $
High Medium Low*
Development $
Low* Medium High
Scalability Low Medium High*
Chapter 2 13
II. World Wide Web History:
CERN 1989 (hypertext concept) Angels and Demons?
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 14
How the Web Works Example of 2-tier architecture
Client needs browser (appl layer SW) Server needs web server (IIS or Apache SW)
Process1. User types URL: protocol, server, and file name2. Browser sends HTTP request (request line,
header, body); fig 2-93. Server returns HTTP response (status, header,
body); fig 2-10 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 15
Web Identifying Information 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/web-server.htm
Chapter 2 16
E-mail The most heavily used Internet application! Advantages over regular mail
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 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 17
How E-mail Works www.howstuffworks.com/email.htm cool! Outgoing mail
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 POP: Post Office Protocol
Client requests message to be transferred to mail folders (probably on hard drive)
IMAP: Internet Message Access Protocol (GroupWise)
Chapter 2 18
E-mail Headers (Underneath)
Received: from mailgate.indstate.edu by isugw; Wed, 29 Aug 2001 09:14:46 -0500 Received: from befac.indstate.edu ([139.102.15.23]) by mailgate.indstate.edu (8.11.2/8.11.2) with ESMTP id f7TEFnb11406 for <[email protected]>; Wed, 29 Aug 2001 09:15:49 -0500 (EST) Received: from BEFAC/SpoolDir by befac.indstate.edu (Mercury 1.48); 29 Aug 01 09:14:46 utc-5 Received: from SpoolDir by BEFAC (Mercury 1.48); 29 Aug 01 09:14:44 utc-5 Received: from gideon.gprc.ab.ca (192.139.30.4) by befac.indstate.edu (Mercury 1.48) with ESMTP; 29 Aug 01 09:14:38 utc-5 Received: from gprc1.icn.gprc.ab.ca (gprc1.gprc.ab.ca [172.20.253.244]) by gideon.gprc.ab.ca with
SMTP (Microsoft Exchange Internet Mail Service Version 5.5.2653.13) id RSJPP6DP; Wed, 29 Aug 2001 08:14:11 -0600 Received: from 32377 ([172.20.7.59]) by GPRC.AB.CA (PMDF V5.2-33 #37300) with SMTP id <[email protected]> for [email protected]; Wed, 29 Aug 2001 08:13:14 MST Date: Tue, 28 Aug 2001 12:05:18 -0600 From: ww <[email protected]> Subject: Text To: [email protected] Message-id: <[email protected]> MIME-version: 1.0 X-MIMEOLE: Produced By Microsoft MimeOLE V5.50.4133.2400 X-Mailer: Microsoft Outlook Express 5.50.4133.2400 Content-type: multipart/alternative; boundary="----=_NextPart_000_0007_01C12FB9.B497FF80" X-Priority: 3 X-MSMail-priority: Normal
Chapter 2 19
3-Tier E-mail Use browser to get mail; see fig 2-12 Replace email client with web browser
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 20
ISU E-mail Mess! Eudora, Outlook Express, Netscape Messenger e-
mail clients HTML mail (Hotmail, Yahoo, Juno, etc) Portal (http://myisu.indstate.edu)
[email protected] is primary student email Username@citrine went away
GroupWise (mail,calendar,tasks,shared data) 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 21
Discussion Groups E-mail based
Subscribe to discussion group To: [email protected] Subscribe mis430-L firstname lastname
Send mail to group 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 22
Discussion Group Commands Each list processor is different, but
many use common commands to 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 http://web.indstate.edu/it/tech-supp/docs/
listproc.htm
Chapter 2 23
III. Other Applications FTP – File Transport Protocol
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) SDSNT and hackers: anonymous FTP
allowed initially with write access – ugh!
Chapter 2 24
Other Applications, contd. Telnet: log on as terminal over the Internet
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 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 25
Other Applications Videoconferencing (fig. 2.14)
Real-time audio and video over Internet MS NetMeeting is popular H.320 and H.323 protocols
Webcasting One-way videoconferencing RealPlayer and MS Media Viewer popular WebEx http://webex.com/ for demo
Bandwidth is key for both! 28.8k, 56k, 128k, 300k, faster
Chapter 2 26
Mgt Focus 2-3: Alabama ADRS ADRS has 800 employees in AL
serving patrons all over the state Uses IP H.323 videoconferencing to
save travel costs Ex: Weekly 90-minute meeting attended
by videoconference instead of driving 100 mi.
IP saves money over previous ISDN dialup connection
