From: Paul Guyot (pguyot_at_kallisys.net)
Date: Sat Jul 10 2004 - 22:06:36 PDT
Aux environs du 10/07/04 à 23:24 +0200, sous le titre "[NTLK] NPDS
via GPRS via Bluetooth...", noiseiskinky prit sa plus belle plume
pour écrire les mots suivants:
>Then I've tryied to make a GPRS connection (just following my
>newton-retro-mobile-server idea :)) and try to connect to NPDS using
>the IP address assigned by the provider. Everything seems to works
>for some times after that every connection try fail and server is not
>reachable.
You very probably cannot have a GPRS-based (NPDS) server. Let me explain why.
In the IPv4 world we live in, each host is assigned a 32 bits address
(called IP address or often IP for short).
There are two kind of addresses. Routable addresses are non-routable addresses.
Each routable address is unique. If you want to access to NewtonTalk
website with the form to go to vacation mode, your computer needs to
connect to the computer at IP 69.10.136.106. There cannot be more
than one computer with that IP because otherwise we couldn't figure
out where to send your request. In other words, routable addresses
are routable because they are not unique.
Non-routable addresses are not unique and not ... routable. There are
three ranges for these addresses. They start with 10., 172. and
192.168. (actually, not every addresses starting with 172. are non
routable).
My Newton which runs NPDS has the IP 10.0.1.202 (I think). But to
access it, you actually connect to the IP 82.66.90.159 which is the
IP of my Airport Base Station. The Airport Base Station does what is
called Network Address Translation or NAT for short. It forwards
requests and replies so that my Newton and my PowerBook can connect
to the Internet and can run servers. For example, when it sees a
request for TCP port 8080, it forwards it to my Newton because my
Newton runs NPDS on this port. Please note that I had to configure my
base station manually to do this. The NPDS Networking Page explains
how to do it.
This allows me to have several machines "connected" to the Internet
while my Internet provider only gave me a single IP. But in fact,
only one machine is connected to the Internet, my Airport Base
Station.
Most GPRS network providers (if not all) do not allocate a routable IP to each:
- mobile phone.
- computer connected to the mobile phone.
It would mean too many IP addresses and these are scarce nowadays.
They actually do NAT. They have a device like my Airport Base Station
in their buildings that translates everything so your Newton can
connect via your phone to the Internet. When you connect to
NewtonTalk web server from your Newton, newtontalk.net webserver does
not see a request from 10. something (or 192.168. something, or 172.
something), but instead a request from a routable IP address. It then
replies to this routable address which is in fact the address of the
NAT device of your GPRS provider, and their NAT device forwards the
reply back to you.
The main difference with a GPRS access and NAT done with a device at
home is that you cannot configure their device doing NAT so it would
forward requests on a given port to your Newton to let your Newton
serve web pages.
In fact, going through NAT devices is the main networking problem of
today's Internet and should be solved with IPv6 (next generation of
Internet Protocol where addresses are 4 times longer, allowing 2^96
more hosts and thus making NAT useless).
Actually, I was mentioning problems with ZeroConf (Rendezvous). NAT
is one of the reasons why Rendezvous doesn't work as well as
AppleTalk: Rendezvous service publishing goes through NAT devices,
but the actual communication sometimes cannot be established because
it cannot go through NAT devices, while AppleTalk service publishing
only goes through NAT devices if the actual communication can go
through them as well.
Just before the wars with the Eskimos, Internet accesses with a
routable IP address were called Full IP Internet accesses. GPRS
providers do not give you a Full IP Internet access. It tastes as if
you were on the Internet, but you are not.
Paul
-- Philosophie de baignoire - consultations sur rendez-vous. NPDS/NewtonOS: http://newton.kallisys.net:8080/ Apache/FreeBSD: http://www.kallisys.com/ Worldwide Newton Conference 2004: http://wwnc.newtontalk.net/ -- This is the NewtonTalk list - http://www.newtontalk.net/ for all inquiries Official Newton FAQ: http://www.chuma.org/newton/faq/ WikiWikiNewt for all kinds of articles: http://tools.unna.org/wikiwikinewt/
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