engs 112 lecture 2 html primer see text or web for more information and examples
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ENGS 112Lecture 2
HTML Primer
See text or web for more information and examples.
HTML is HyperTex Markup Language
HTML is a “specialization” of SGML
HTML is a language for describing how web pagesshould look. HTML has some constructions forforms, frames, etc that make it a bit more dynamic.
HTML is very simple....we’re going to go overonly the basics...other sources:
- Dietel- read the source of other pages- web HTML manuals and how-tos
Basic syntax of an HTML construct
• HTML uses “tags”• tags typically have a beginning and a closing version.• example....every html page should start with the tag
<html>
and end with
</html>
Not essential but good style.
Basic structure of an HTML page<html><head><title>Our first page!!</title></head><body>Blah, blah, blah</body></html>
Some tags
Headings <h1>...</h1>, <h2>.....</h2>,....
New paragraph <p>
Line Break <br>
Horizontal rule <hrule>
Let’s try them now....
Links and URL’sWeb link construction
<a href=“http://www.cnn.com”>CNN’s web site</a>
<a> </a> HTML anchor tag
http:// is the protocol or scheme
www.cnn.com is the server name
anything following that is the path name
“CNN’s web site” is the anchor
Absolute and relative links
<a href=“http://www.dartmouth.edu/~gvc/”>Dartmouth</a>
is an absolute reference to a web page.
<a href=“somefile.html”> Another link</a>
is a relative link.
Text properties<b> </b> boldface
<i> </i> italics
<blink> </blink> blinking
<u> </u> underlining
<strike> </strike> striked out
Backgrounds
<body bgcolor=“#rrggbb”>
OR
<body background=“some url or relative file name”>
Where can you get some fun backgrounds?
Let’s do some searches!!!!
Adding images
Image formats most browsers can view
jpeg, jpg Joint Picture Experts Group
tif
gif
.....etc
<img src=“some URL or filename” alt=“picture”>
Images as anchors for links
<a href=“URL”><img src=“ULR”></a>
Let’s do an example......
URL’s and Internet Names, addresses, etc
www.dartmouth.edu is the name of a server
The name is for human consumption...the internetuses a four number address to identify all “hosts”on the internet.
129.170.16.79
Each number is between 0 and 255.
Let’s buy an internet domain name!!!
Visit www.nsi.com to see what names aretaken, who owns a particular name, or buy a namefor yourself!!!
Domain names are hot commodities....ebay auction
Name brands and common words are all taken.
All two and three letter combinations are gone.
This is the “real estate” of cyberspace!!!
Networked Services
ApplicationsWWWStreaming data – audio and videoInternet telephony and videoconferencesNetworked gamesClient/serverSensor networksBroadcast TV – video on demand
Quality of Service (QoS)
Constant bit rate (CBR)Variable bit rate (VBR)End-to-end delays, latencyBit error ratesAdmission policy and blocking probabilities
Engineering Challenges of Different Content Types
Content Bandwidth Bursty QoS?
Web, data Medium Yes No
Voice Low Yes Yes
TV, video High No Yes
Monitoring Variable No No
Network Elements
Links and switches – abstractions as graphs and queues
Service characterizations –
total delay = trans + prop + qd + proc
Network Mechanisms
Multiplexing – sharing a common channel/resource
Time-division multiple access TDMAStatistical multiplexing Spatial multiplexingFrequency-division multiple accessCode-division multiple access
Network Mechanisms
Switching
circuit switchingpacket switchingdatagram network vs virtual circuit
switch design – Clos and other switch designs
Packet SwitchingSend “packets” into the network, routing each packet individually, like the post office. Packets are “routed”through the network, sorted at “switches”.Requires no setup time but no guarantee of service!!
Good for telephones, bad for web browsing!!!!
Network Mechanisms
Error control - detection vs correction
parity bitscyclic redundancy codes
replication for error correctionBCH and Reed-Solomon codes
error detection and correction protocolsretransmission protocols
Network Mechanisms
Flow control
Congestion controlproblems with long haul, high speed networksrate control (open loop)
Resource allocation
Why is “convergence” achallenge?
Convergence of entertainment, telecommunications andcomputing industries.
Telecom is set up for voice.
Entertainment requiries audio and video QoS.
Computer communication is based on packet switching.
OEE (Due Friday, April 14)
Walrand page 93+
1.3.4.12.16.20.25.
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