Internet / Intranet
Fall 2000
Class 10
Class 10 Agenda
Milestone#4 - Discussion
Presentations
Cookies
Misc. Topics
Wireless Devices: WAP / WML
Wrap-Up
Brandeis University Internet/Intranet Spring 2000
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Cookies Revisited
Cookies Are Name Value Pairs
Passed in the HTTP Header
Cookies Have Associated Expiration
Session (Default)
Date / Time
Associated With a URL Path, Not a Page!
Allows Passing Parameters Between Web Pages
Thus Cookies are Used to Provide State
Information to a Stateless Protocol
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Cookie Jar
Cookie Storage
Internet Explorer
c:\windows\cookies
Each Has its Own File
Netscape Navigator
cookies.txt (all kept in the file)
Limits
20 Cookies
4K Per Name/Value Pair
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More Cookies
Cookies are Traditionally Set By Server
Set-Cookie
Browser is Responsible For Maintaining Them
Stored On Client’s Computer
Passed to Server When Web Site is Revisited
HTTP-Cookie
Cookie Attributes
Name – The Name of the Cookie
Subsequent References to Same Name Overwrites Cookie
Attributes
Value – The Value of the Cookie Identified by Name
Expiration – When the Cookie Expires
No Date Specified – Cookie Expires at End of Session
Past Date/Time – Delete the Cookie
Future Date/Time – Delete the Cookie After This Date
Example
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Cookie Bits
Example Cookie
Set-Cookie: tollhouse=favorite;expires=Thursday,
16-Mar-2000 00:00:00 GMT;path=“”
Note That Date Must Follow This Format:
Weekday, DD-MMM-YYYY HH:MM:SS GMT
RFCs specify GMT as the mechanism for handling
time problems on the Internet
HTTP-Cookie Only Sends Name/Value Pair
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Cookies - JavaScript
Cookies Can be Set in JavaScript
document.cookie = “ “
Use Date.toGMTString() to set expiration date
E.g.
document.cookie = “version=1.0; ” + “expires=“ + edate.toGMTString();
To Read a Cookie Value in JavaScript
var allcookies= document.cookie;
var pos = allcookies.indexOf(“version=“);
if (pos != -1) {
var start = pos +8;
var end = allcookies.indexOf(“;”,start);
if (end == -1) end = allcookies.length;
var value = allcookies.substring(start,end);
vervalue = unescape(value);
}
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Cookie Structure
Path Information
Default is to Send Cookie to Any URL in the Same Directory or
any Subdirectory of the Page Which Set Cookie
Path Attribute Can Request That Cookie Be Sent to All URLs in
Path (and its Subdirectories)
Only Paths That are a Prefix of Current URL are Allowed
If Cookies Overlap, All are Sent.
Ordered by Most Specific to Least Specific Match
Domain Attribute – Allows Cookies to Be Shared Across Sites
Must Be Part of Same Domain
E.g. boston.brandeis.edu and lab.brandeis.edu are part of the
same domain but may be different servers
Secure – Only Sends Cookie If Secure Protocol is Used (e.g.
SSL)
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Security Issues
Protections:
Cookie Can Only Store Information Already Known to Server
Can’t Access Hard Disk, etc.
Data Only – Not Executed by Client Machine
Data Can’t Be Shared Across Sites
Concerns:
Of Course This Assumes That Browser Follows the Rules
Browser Can Store Sensitive Information
E.g. If Server Doesn’t Set Secure Tag, a Credit Card # May Be
Passed in Clear to Another Page in Same Path
“Invisible” to Users
Paths Are Not Always Obvious
E.g. Multiple Sites Receive Graphics From DoubleClick Server
DoubleClick Can Now Gather “Cross-Site” Information
Zealous privacy folks advocate turning off cookies
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Performance Tuning / Testing
Performance Improvements
Server Scripting, etc. Degrades Server Performance
Minimize Reliance on Server Scripting
“Compile” Frequently Used Documents
Increase CPU, Disk, Caching, Internet Pipe
Multiple Servers (Basic)
Distribute Pages Across Servers
Multiple Servers (Advanced)
Route Requests to Multiple Servers
Round Robin DNS
DNS Server Returns a Different IP Address Each Time
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Web Robots
Spiders, Crawlers, and Bots, Oh My!
Programmatically Visit and “Analyze” Web Sites
Gather Information From The Site
Typically as Data For Search Engines
Validate Links For Currency
Follow Links
Robot Protocol (Voluntary)
robots.txt – In top-level Directory of a Site
User-Agent: Names of Robots or *
Disallow: Parts of Hierarchy to Disallow or /
<META Name=“Robots” Content=“NoIndex, NoFollow”>
Or Index, Follow – Tells Robot Whether or Not to Index Site,
Follow Links
User-Agent Typically Identifies Robot
Accesses to robot.txt
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Building Web Robots
Issues When Building a Robot
Follow Web Exclusion Rules
Parsing
Ability to Parse HTML For Target Info. Identify Links.
Iteration
Search Strategies:
Breadth First
Depth First
Avoid Endless Loops
Don’t Revisit Links Already Visited
Don’t Follow Outside Links?
Termination
Depth, Sites Visited, Time, High Proportion of Duplicate Links
Tools For Bulding Robots
JavaScript
VB 6 – Internet Transfer Control and Web Browser Control
Others
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Trends toward smaller devices
Moore’s law
History of Computers
trend toward smaller devices
trend toward cheaper devices
processors in more and more devices
TCP/IP can expand well beyond PCs
5 year time frame ( Gartner Group )
a billion mobile phones ( US lags behind Europe and
Asia )
over half of Internet access through non-PCs
M-Commerce replaces E-Commerce
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Wireless Internet
HDML - 1995
Handheld Device Markup Language
subset of HTML
I-mode - Japan
uses a tag language based on HTML
cHTML
7 million users
WAP/ WML
currently at 1.3 ( 1.1 widely supported )
protocol extends Internet to Phones
specialized for smaller screens
GPRS general packet radio switching
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Wireless ‘Non-Internet’
continued investment - limited commercial success
Bluetooth
develop a wireless standard for all devices
low earth orbit satellites
must be in low orbit
big time failures (Iridium, Globalstar) Teledisic ?? ( Bill Gates and Craig McCaw )
Many premature predictions about wireless
1993 was supposed to be the year of wireless
issues of latency, reliability, security, processing
power
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WAP Application Architecture
WAP Gateways
connect Wireless Messages with Internet
Leverage the Internet plumbing
Wireless requested converted to HTTP
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WAP Gateways
Implement WAP protocol stack layers
account for security and sessions
convert WSP -> HTTP
Encodes HTTP heads as binary tokens
Domain Name Resolution
HTML to WML conversion
limited success so far
encode WML content
Security
Cache frequently accessed content
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WAP Gateways
offered by all major vendors
Noika
Motorola
Ericsson
Kannel ( Open-Source WAP Gateway )
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WAP Protocol Stack
derived from the OSI Reference Model
Application Layer ( WAE )
Session Layer ( WSP )
Transaction Layer ( WTP )
Security Layer ( WTLS )
Transport Layer ( WDP )
Bearers (SMS, CSD, USSD, CDMA, CDPD .. Others )
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Phone emulators
Simulate phone usage ( see example )
not perfect approximation
used to develop wireless applications
Noika WAP Toolkit
image support
Phone.Com ( UP.Simulator )
Ericson
Motorola
VoxML ( precedes VoiceXML )
host of other tools
Microsoft Mobile Explorer
provide a useful tool for test/debug cycles
still at the early stages
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WAP Devices
limited processing power
limited RAM
embedded Browsers
do not behave the same
cache requests
emulators simulate ( do not forget to clear )
lots of latency
currently 9600 bits per second
versus 56 kilo bits per second wired
Deja-vu for programmers
back to 64K barriers
machine code
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Configuring Servers for Wireless
add MIME types (.htaccess in Apache, IIS Registry)
wml - text/vnd.wap.wml
wlmc - application/vnd.wap.wmlc.
wmls - text/vnd.wap.wmlscript
wmlsc - application/vnd.wap.wmlscriptc
wbmp - image/vnd.wap.wbmp
Shore.net Apache server supports wml
Call server scripts within documents same as
before
support for CGI/Perl
Cold Fusion
JSP/ASP
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WML
designed for small displays
deck of cards metaphor
replaces <BODY> concept
XML
all docs need an XML declaration and DTD
all documents must be well formed
Text Formating
<p> </p> used for all text
<br/> breaks text
support for styles
Bold <b></b>
Italitic <I></I>
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WML
anchor tags wrap links same as HTML
<go> tag indicates action when link is selected
# used to select other cards in the deck
WML Input
<input name =“var” > tag
variables then displayed with ‘$’ delimiter
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More WML
<prev> tag sends the user back to the previous
document
<do> associates an action with a given element
<do type=“prev” label=“Previous”>
<prev/>
</do>
Creates a Previous operation for a softkey
<select> element
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Wireless Scripting
WMLScript - based on ECMAscript
useful for validation
WML tags support events
timers
card supports three main events
onenterforward
onenterbackward
onTimer
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WML GET/POST request
WML supports HTTP Get & Post
GET Request
append data as parameter to the URL
use WMLScript
POST Request
specify as an attribute in the <go> tag
<go method=“post” href=“somescript.pl”>
<postfield name=“product” value=“$(product)”/>
</go>
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WML Images
wireless bitmaps (WBMP)
monochrome
initially needed to convert bits in GIF and JPG files
tools are emerging
Nokia toolkit supports
plug-ins exist for most major tools ( Photoshop,
Paintshop)
watch out for latency !!!
Large bitmaps
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Usability
Terse documents
WML apps need to deliver bullet points
short text labels
minimize data entry
sites need high personalization
NOT the Internet on a cell-phone
New applications will be created
Still significant browser differences
tags do not work in a uniform way
significant differences in screen size
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WAP Resources
WAP FAQ http://www.wap.com
WAP forum http://www.wapforum.org
Professional WAP ( Wrox Press )
ISDN 1-861004-04-4
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Presentations
Mirrors Real Life Situations
CoWorkers, Audience Have Different Backgrounds
Relevance to Audience Varies
Some With Lots of Experience – Want Details
Management vs. Technical Personnel
Strategy:
Give Enough Background to Identify Key Issue
Most Will File it Away for Future Reference
Identify Target Audience
Give “Meaty” Info
Be Judicious With Time
Can’t Cover Everything
Provide Reference Material
Those Who Want to Learn More Can
Most Will Want Info at Some Point in Future
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Career Advice
Software Engineering Growth Paths
Require Ability to Bridge Gap Between Management and
Technical
Management
Concerned With Practical Implications, Not Technical Details
Technical
Knowledge and Ability to Implement Task
“Political”
Different Personalities Have Different Expectations
Valuable Skills
Technical Knowledge
Customer Requirements
Development Schedule / Quality / Maintenance / Cost
Mentorship
Communication
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Wrap-Up
Ongoing Resource: evan@mkat.com
General Questions
Jobs, etc.
Grading
ShoreNet Accounts
Class Web Site
Enjoy Your Break!
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