Frustration over congestion issues in the Internet infrastructure and the high latency that results in slow browsing has led to an alternative, pejorative name for the World Wide Web: the World Wide Wait. Speeding up the Internet is an ongoing discussion over the use of peering and QoS technologies. Other solutions to reduce the World Wide Wait can be found on W3C.
Standard guidelines for ideal web response times are (Nielsen 1999, page 42):
0.1 second (one tenth of a second). Ideal response time. The user doesn't sense any interruption.
1 second. Highest acceptable response time. Download times above 1 second interrupt the user experience.
10 seconds. Unacceptable response time. The user experience is interrupted and the user is likely to leave the site or system.
These numbers are useful for planning server capacity.
Saturday, 29 December 2007
Caching
If a user revisits a web page after only a short interval, the page data may not need to be re-obtained from the source web server. Almost all web browsers cache recently-obtained data, usually on the local hard drive. HTTP requests sent by a browser will usually only ask for data that has changed since the last download. If the locally-cached data is still current, it will be reused.
Caching helps reduce the amount of web traffic on the Internet. The decision about expiration is made independently for each downloaded file, whether image, stylesheet, JavaScript, HTML, or whatever other content the site may provide. Thus even on sites with highly dynamic content, many of the basic resources only need to be refreshed occasionally. Web site designers find it worthwhile to collate resources such as CSS data and JavaScript into a few site-wide files so that they can be cached efficiently. This helps reduce page download times and lowers demands on the web server.
There are other components of the Internet that can cache web content. Corporate and academic firewalls often cache web resources requested by one user for the benefit of all. (See also Caching proxy server.) Some search engines, such as Google or Yahoo!, also store cached content from web sites.
Apart from the facilities built into web servers that can determine when files have been updated and so need to be re-sent, designers of dynamically-generated web pages can control the HTTP headers sent back to requesting users, so that transient or sensitive pages are not cached. Internet banking and news sites frequently use this facility.
Data requested with an HTTP 'GET' is likely to be cached if other conditions are met; data obtained in response to a 'POST' is assumed to depend on the data that was POSTed and so is not cached.
Caching helps reduce the amount of web traffic on the Internet. The decision about expiration is made independently for each downloaded file, whether image, stylesheet, JavaScript, HTML, or whatever other content the site may provide. Thus even on sites with highly dynamic content, many of the basic resources only need to be refreshed occasionally. Web site designers find it worthwhile to collate resources such as CSS data and JavaScript into a few site-wide files so that they can be cached efficiently. This helps reduce page download times and lowers demands on the web server.
There are other components of the Internet that can cache web content. Corporate and academic firewalls often cache web resources requested by one user for the benefit of all. (See also Caching proxy server.) Some search engines, such as Google or Yahoo!, also store cached content from web sites.
Apart from the facilities built into web servers that can determine when files have been updated and so need to be re-sent, designers of dynamically-generated web pages can control the HTTP headers sent back to requesting users, so that transient or sensitive pages are not cached. Internet banking and news sites frequently use this facility.
Data requested with an HTTP 'GET' is likely to be cached if other conditions are met; data obtained in response to a 'POST' is assumed to depend on the data that was POSTed and so is not cached.
Link rot and web archival
Over time, many web resources pointed to by hyperlinks disappear, relocate, or are replaced with different content. This phenomenon is referred to in some circles as "link rot" and the hyperlinks affected by it are often called "dead links".
The ephemeral nature of the Web has prompted many efforts to archive web sites. The Internet Archive is one of the most well-known efforts; it has been active since 1996.
The ephemeral nature of the Web has prompted many efforts to archive web sites. The Internet Archive is one of the most well-known efforts; it has been active since 1996.
Academic conferences
The major academic event covering the Web is the World Wide Web series of conferences, promoted by IW3C2.
WWW prefix in web addresses
The letters "www" are commonly found at the beginning of web addresses because of the long-standing practice of naming Internet hosts (servers) according to the services they provide. So for example, the host name for a web server is often "www"; for an FTP server, "ftp"; and for a USENET news server, "news" or "nntp" (after the news protocol NNTP). These host names appear as DNS subdomain names, as in "www.example.com".
This use of such prefixes is not required by any technical standard; indeed, the first web server was at "nxoc01.cern.ch", and even today many web sites exist without a "www" prefix. The "www" prefix has no meaning in the way the main web site is shown. The "www" prefix is simply one choice for a web site's subdomain name.
Some web browsers will automatically try adding "www." to the beginning, and possibly ".com" to the end, of typed URLs if no host is found without them. Internet Explorer, Mozilla Firefox, Safari, and Opera will also prefix "http://www." and append ".com" to the address bar contents if the Control and Enter keys are pressed simultaneously. For example, entering "example" in the address bar and then pressing either just Enter or Control+Enter will usually resolve to "http://www.example.com", depending on the exact browser version and its settings.
This use of such prefixes is not required by any technical standard; indeed, the first web server was at "nxoc01.cern.ch", and even today many web sites exist without a "www" prefix. The "www" prefix has no meaning in the way the main web site is shown. The "www" prefix is simply one choice for a web site's subdomain name.
Some web browsers will automatically try adding "www." to the beginning, and possibly ".com" to the end, of typed URLs if no host is found without them. Internet Explorer, Mozilla Firefox, Safari, and Opera will also prefix "http://www." and append ".com" to the address bar contents if the Control and Enter keys are pressed simultaneously. For example, entering "example" in the address bar and then pressing either just Enter or Control+Enter will usually resolve to "http://www.example.com", depending on the exact browser version and its settings.
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