[thelist] What goes on under the hood of the Internet?

Scott Dexter sgd at ti3.com
Thu Sep 7 15:11:36 CDT 2000

let's take this a little further, shall we? =)

Down at the data level, and at email and WWW levels, your own Cafe model
works here. Yup. In fact looking at your diagrams gave me flashbacks to my
networking classes.

1) You connect to your ISP
	Out through your phone line, your computer is joining a table at a
cafe. Sitting at this table are possibly hundreds of other people connected
through their phone lines. Now, considering there is no way the cafe could
ever have a table big enough for everyone at this table, there is a limit to
the number of seats. So when you 'sit down,' you're sitting in a chair
someone else might have had not ten minutes ago. --This is your dynamic IP
address; your designated seat (IP) at this table (ISP) in this cafe

2) How traffic gets out
	All of the tables in our cafe are connected via 'magic seats' (for
lack of a better term, I should just call them routers --that's what they
are). As you are talking at the table, everything you say (packet) has
attached to it your table+seat number (IP address), and the table+seat
number you want to talk to. Talking to a seat at your table is like placing
the mustard on a lazy susan and spinning it. The correct seat will pick it
up when it comes by. As it spins, you pick up anything that has your seat
number on it. --Though you could 'see' what others at your table are passing
around, you ignore it. (Someone who eavesdrops is called a packet sniffer).
If the seat happens to be at another table, the 'magic seat' at your table
passes your mustard along to the next. He also keeps an eye on the next
table's lazy susan looking for anything that belongs at your table. Here is
where classic routing algorithms come into play, as each table (ISP) can be
connected to multiple other tables. The 'magic seats' (routers) maintain
intelligent information to determine which table to send your sentence to.
You say something, and it gets passed table-by-table to the right seat,
where a reply is said and it comes back (more or less) the same way. Slow
tables happen ;) Since your table+seat number is attached to everything you
say, the other tables now how to find you. --Its like a return address on a
piece of mail. Performing a 'ping' tests how fast the table+seat you want to
talk to can get back to you; a 'traceroute' shows which tables are used and
how fast they can pass things along.

3) Email & WWW
	Some seats at your table have specific duties. When you say "email
my mom at table 23" to the email chair (server) at your table, it asks where
'table 23' is, and the email chair it needs to talk to. (This is through
DNS, which has been mentioned already.) Then it tries to send your email to
the email server at table 23. If he's swamped with other email, or your
email server has a hard time finding out where table 23 is (did they move it
out to the patio??), it holds on to your message and tries again multiple
times over certain intervals (human configurable, a common setting is to
retry for 48 hrs). When the email is delivered, the email server at table 23
holds onto it until your mom asks it if she has any new mail. More
information is contained on the email envelope (email headers) than what is
sent out above (packets). Your table+seat number for sure, but also
information the email chairs use to talk amongst themselves, like "this came
from Peter at table 1423," and "the email chair at table 56 was used to pass
it along at 2:53pm."
	When you want to talk to a www chair (server), you ask for the
table+seat number (IP address), and then send a kind request for information
(I'll call this the URL, though technically a URL encompasses the IP
address). While you are waiting, your request is being passed along to the
www server at the far table. The www chair looks at your request, packages
an answer, and sends it back. He's very curt, and has a bad case of amnesia.
He has to be able to handle lots of requests from lots of seats, so he only
replies back with what you asked for, ends the conversation, and instantly
forgets he talked to you. You have to ask him again if you want more, but
trust me, he's forgotten all about you and you have to ask very specifically
and remind him who you are each time. Such is stateless communication. If he
likes you, he'll want to remember you by sending you some cookies. Sending
them back triggers his memory and he's not so forgetful anymore. What he
wants to remember about you determines what kind of cookies you get. Not
everybody likes cookies, though. ;)

4) You disconnect from your ISP
	Simple; you get up and leave the table (hang up the line). If
there's anything left on the lazy susan for you, it eventually gets thrown
away because its been there too long.

hope this helps, i winged it
work: http://www.ti3.com/
non: http://thinksafely.org/

> -----Original Message-----
> From: Anthony Baratta [mailto:Anthony at Baratta.com]
> When you want to talk to www.evolt.org - your computer does a 
> "shout-out" for
> www.evolt.org to your local Domain Name Server. This 
> shout-out comes back as an IP
> address. Then your machine sends a "Where are you?" message 
> to the IP Address you
> just got from the Domain Name Server. If there is a response 
> from your target IP
> Address, you then begin a communication.  

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