Basic Internet addressing

Hosts and IP addresses

Email addresses

	user@hostname

	user@subdomain

	user@ibm.com

	user@computing.dcu.ie

Any "." to the LHS:

	name.surname@computing.dcu.ie

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

Telnet and FTP

	telnet hostname
	telnet logingateway.computing.dcu.ie

	ftp hostname
	ftp filegateway.computing.dcu.ie

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

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

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

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

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

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

http://computing.dcu.ie/alumni/

http://computing.dcu.ie/ALUMNI/

See My CGI Error Handler to replace "404 Not Found"

"Why are Internet addresses so complicated?"

Some people still say: "Why are Internet addresses so complicated? What's with all this http @ //www//com stuff?"

Maybe I can't see it, but to me, Internet addresses are the simplest, most logical, and most easy to guess form of addressing ever invented, far easier than postal addresses, and a million times easier than telephone numbers.

Internet addressing is:

1. Alphanumeric, allowing direct maps to English. As opposed to awful 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 on earth is anybody to remember something like that?? Especially when it changes every couple of years.).

   Funny enough, on the Internet some people, notably Compuserve in email addresses and Geocities in web page addresses, chose to disable the alphanumeric ability, and make everything numeric. I'm sure their misdirected email and "web page not found" errors are far higher as a result. Even the University of Cambridge, when I was there, was enforcing a ludicrous numeric system so that my userid was:   mh10006   - this despite the fact that the userid   humphrys   was unused and available on all machines in the university.

   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.

   
   

2. 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.

   
   

3. 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.

   
   

4. 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?

   
   

5. 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  

   
   

6. 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

1. 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)
     

2. 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.

3. For both of these, see now phone number on my home page.