IPv6 over Wireless LANs
With the increase in available bandwidth to 802.11b (wireless LAN) devices
rising, there is considerable interest in use of such technology for
enabling network access to portable devices such as laptops and PDAs.
With many students buying their own laptops for their degree studies,
wireless LAN (or WLAN) access is becoming ever more topical.
The current WLAN standard, 802.11b, allows 11Mbit/s between an access point
and a single wireless device. This theoretical speed is rarely reached,
and drops as more hosts attach to the same access point, but the imminent
arrival of 802.11a, with a speed in excess of 50Mbit/s, will further
heighten interest. The 802.11a equipment also uses a higher frequency
space than Bluetooth, so should be less of a concern for interference.
Each of the Bermuda project sites has an 802.11a WLAN deployment.
As a layer 2 access medium, WLANs will transport IPv6 just as readily
as IPv4. Thus you can run IPv6 over the same equipment, or run IPv6-only
networks over wireless.
The interesting choice comes in whether you offer a flat, non-routed network,
such that all hosts will retain the same IP address while connected, or
run a routed network, such that each access point may offer a different
IP address range. In the latter case, you require Mobile IP to allow
connections to persist as the device changes its underlying IP address.
In order for a device to attach to a different access point as it moves,
it must share the same wireless network name. Wireless range varies
considerably indoors, being notably affected by walls - one wall will
reduce the signal, two will make it weak, three will kill it, though
of course the wall thickness is a factor. By appropriate placement of
access points (and non-conflicting setting of the channel used by each
point), it is possible to maintain "hot spot" connectivity over a wide
area. This is suitable for a flat, non-routed network.
If however, the WLAN deployment is being made to test Mobile IPv6, then
access points will need to be configured with different wireless network
names, and advertise different IPv6 network prefixes. Furthermore, one
host/router will need to act as a home agent for the mobile device,
allowing it to be addressable by a single home IPv6 address while adopting
different care-of addresses from its currently bound access point while
roaming.
Mobile IPv6 can be demonstrated on a laptop, but PDA demonstrators are
more interesting as an example of offering IPv6 connectivity to more
compact, mobile devices. While it is again possible to offer IPv6 for
the handheld device on a flat IPv6 network, for testing Mobile IPv6 a
PDA and WLAN deployment is an excellent environment.
The Compaq iPAQ can have Linux installed - there are instructions at
handhelds.org. If replacing the
WinCE with Linux, you should ensure you take a backup of your WinCE
system to flash memory before continuing (assuming you want to return to
WinCE later). Once Linux is installed, many distributions will already
include IPv6 support. For Mobile IPv6, you need to compile one of the
available implementations, e.g. from HUT, for the StrongARM architecture.
There are currently very few good Linux PDA applications (for X11), but
the system is a good developer test environment. You can of course open
a window from your PDA on a remote host for easy system editing (though
there is a nice fold-out keyboard available for the iPAQ).
|
