Ad-hoc Networking

[Morgan Collett]

On Thu, Apr 24, 2008 at 1:27 AM, John Gilmore <gnu at toad.com> wrote:
>  Take two such laptops.
>
>  Take them way out into the country so they can only communicate with
>  each other.
>
>  There are no access points.  No laptop is acting as an access point, either.
>
>  Can those two laptops communicate?  Under 802.11b/g, the answer is yes.
>  They are communicating in "ad-hoc" mode.  Each can transmit packets and
>  the other one gets the packets.  (This works for N laptops, not just two.)
>
>  The IETF "ZeroConf" protocols provide for self-assignment of IP
>  addresses in such a case.  (The same thing happens if you plug two
>  laptops together with a short Ethernet cable and no DHCP server.)
>  Once they self-assign IP addresses, the laptops can talk at an IP
>  level.  They can send unicast, multicast, and broadcast packets to
>  each other.  (If you look in the Mac Control Panel, you'll see this
>  reported as a "self-assigned IP address", with a warning that you
>  probably aren't connected to the global Internet, since most of the
>  time that was what you probably expected.)
>
>  Does the OLPC Presence Service work in such a case?

Yes, that is exactly what telepathy-salut does, using avahi. You can
also take two Nokia N800s and chat between them, or two laptops at a
conference running a telepathy-based jabber client like Empathy, and
chat between them - all ad-hoc, no infrastructure required.

Morgan