Basic Internet addressing

Hosts and IP addresses

Email addresses

	user@hostname

but more commonly:

	user@subdomain

	user@ibm.com

	user@computing.dcu.ie

Case irrelevant.

Any "." to the LHS:

	name.surname@computing.dcu.ie

are just cosmetic. They do not represent subdivisions, as "." to the RHS does.

Site can implement any naming scheme it likes on LHS of the @ sign.

Web addresses (URLs)

	http://hostname/path
	http://hostname/directory/subdirectory/file.html

	http://computing.dcu.ie/
	http://computing.dcu.ie/Research/
	http://computing.dcu.ie/Research/Multimedia-Group/
	http://computing.dcu.ie/Research/Multimedia-Group/people.html

	http://computing.dcu.ie/~user/
	http://computing.dcu.ie/~user/publications.html

Path may map 1-1 to actual path on disk.
Or may not (when web pages served up by database).

Case irrelevant in the http: part and the hostname part.

Case may be relevant in the path part only. e.g. UNIX server maps 1-1 with file on disk and respects case. Windows server doesn't.

Is case sensitivity a good thing?

CA server

CA server is UNIX but server software now implements case-insensitive username:

http://computing.dcu.ie/~Humphrys/

http://computing.dcu.ie/~HUMPHRYS/

http://computing.dcu.ie/~HUMPHRYS/teaching.html

but not filename:

http://computing.dcu.ie/~HUMPHRYS/TEACHING.html

See Case sensitivity and "404 Not Found"

Internet addresses v. postal / phone addresses

Internet addresses seem to have a number of advantages over postal addresses or telephone numbers.

Internet addressing is:

Alphanumeric, allowing direct maps to English.
As opposed to numeric-only addresses like phone numbers.
(An ad says something like: "14172 - Your new mobile directory enquiries number. The only number you'll ever need." How is anybody to remember something like that? Especially when it changes every couple of years.)
Be careful about imposing all-numeric or other cryptic solutions on your users. When I was a postgrad, I was given the userid mh10006 - despite the fact that the userid humphrys was unused and available. Why increase login failures, failed emails, and 404 Not Found web requests for no reason?
It is interesting to consider that underneath, Internet addressing is actually numeric, but machines have been forced to map text strings to numbers since the earliest days of the Internet.
Guessable. I know IBM's web site is ibm.com. I have no idea what their phone number is, and if told I wouldn't remember anyway.
I don't even know what DCU's phone number is, and I work for them.
Maybe I could remember IBM's phone number if it was 1-800-IBM-CORP. Or does that 1-800 number only work in America? Or should it be 1-800-BUY-IBM? Who knows.
And what is their postal address? I don't know, but I know I'll find all that information at ibm.com.
Variable-length. Your company's website is simply company.com, whether that means bt.com or arthurandersen.com.
It doesn't have to be either squashed into a small number of characters, or expanded to fit a fixed-size field, as with say 1-800 numbers.
Note that some older competing naming schemes weren't as flexible, e.g. BITNET had maximum 8 char names.
Location independent, so don't have to memorise loads of area codes.
You bookmark www.site.co.uk/subsite and the bookmark works, whether you are in the UK, in Ireland, or anywhere at all in the world. Note that you couldn't set up links for other people if it wasn't location independent.
Quick! What's the area code for Belfast? What's the area code for London?
Hierarchical, so we can get to dcu.ie safely and then start looking for the Computer Dept. Addresses often contain a self-description of their place in the hierarchy: comp-dept.western-university.edu.au/staff/dr.smith/phd/references.html
We can also get repeated feedback in our guesses,
e.g. dcu.ie/user failed, so we try dcu.ie
Now we've got to the dcu.ie web home page safely, we can use this as a base from which to explore further and hopefully find a link to user
Dial a wrong number and what's your feedback? Post a letter to the wrong address and what's your feedback?

Variable-length - Note on UNIX 8 char userids

Historically, one area where UNIX/Internet fell down was on userids. Variable-length hostnames were ok, variable-length filenames were ok, but usernames were restricted to 8 chars.

The legacy of this is still with us. e.g. The Solaris UNIX system here allows long usernames, but the log files and other administration tools only display the first 8 chars - which is why undergrad userids are still ugly and squashed.

Could we develop a location-independent, "linkable" phone system?

Something that would be nice: An integrated computer-phone system, such that, once your PC had a mike and speakers and was connected to a free (i.e. not engaged) phone line, you could click on location independent hyperlinks such as:

phoneto:7008059@1.353
phoneto:7008059@1.ie
phoneto:7008059@dublin.ie

phoneto:8059@700.dublin.ie
phoneto:8059@dcu.dublin.ie
phoneto:humphrys@dcu.dublin.ie

phoneto:ca@dcu.dublin.ie
phoneto:dcu@dublin.ie

phoneto:12345678@london.uk

Then you could set up location-independent links for other people. Would require the implementation of a name server system for phones.

This is happening:

There is a location independent, phoneto-like tag WTAI (also here) in the mobile phone protocol WAP.
- wtai://wp/mc;+3531nnnnnnn (ring Dublin number nnn-nnnn, location-independent)
With Skype VoIP, you can embed a callto: tag in regular HTML in a regular web page:
- callto:+3531nnnnnnn (ring Dublin number nnn-nnnn, location-independent)
- callto://+3531nnnnnnn
- callto:skypeuserid (ring Skype userid)
- callto://skypeuserid
callto can launch non-Skype VoIP clients.
For both of these, see now phone number on my home page.
Skype Toolbar now automatically makes clickable any phone numbers seen on screen in IE and Firefox:
Some smartphones now recognise callto. Click callto:number on an iPhone and it makes a normal phone call.