Well before the attacks on the World Trade Center, millions of people
depended on wireless networking to connect to their work environments while
travelling or working remotely. The events of September 11 and their
aftermath deepened our dependence on mobile networking, and made clear the
distinction between mobile and portable computing.
During and shortly after the attacks, cellphones and air interface
communications emerged as our only links to the tragedy that unfolded. In
the days that followed, tens of thousands of officeless workers scrambled to
get re-connected, many of them working from home and makeshift workplaces,
all of them suddenly "mobile."
Observers agreed that September 11 drew attention to a trend that had been
gathering steam for some time. "I think it makes lots of sense for people
with critical jobs to have lots of ways to communicate, and it's a
no-brainer to have at least two devices, such as a Research In Motion [RIM]
e-mail device and a voice cell phone," Alan Reiter, an analyst at Wireless
Internet & Mobile Computing in Chevy Chase, Md. told Computerworld.
Ken Dulaney, an analyst at Gartner Inc. in Stamford, Conn., predicted that
there will be more demands to stay connected and said that "the use of an
adjunct to the notebook will become more popular, not only for disaster but
to keep connected continuously."
Keeping connected continuously suggests the distinction between mobile and
portable computing. "Mobile computing and networking should not be confused
with the portable computing and networking we have today," says former Sun
Microsystems Laboratories engineer Charles Perkins. "In mobile networking,
computing activities are not disrupted when the user changes the computer's
point of attachment to the Internet. Instead, all the needed reconnection
occurs automatically and noninteractively."
[http://www.computer.org/internet/v2n1/perkins.htm]
Staying connected is the goal of the Mobile IP technology being designed by
the IETF's Mobile IP working group. James Kempf and Jonathan Wood have been
deeply involved in working with the Mobile IP working group to design and
implement a virtual tunnel technology that keeps IP-based wireless
communications clear and connected.
Taking Care of Address
A breakthrough in "fast handoff," Kempf and Wood's virtual tunnels keep
wireless devices connected as they physically move between different radio
access points. In the world of Mobile IP, each mobile device maintains an
extra IP address. The spare IP address, known as a care-of-address, changes
whenever the device moves from one subnet to another. The device also has
its address on the home network, called the home address. The problem:
delays associated with changing the care-of-address can result in connection
disruption, especially for delay-sensitive real time traffic such as voice.
"The delay can put people off. We wanted to make it better," recalls Kempf.
The design breakthrough involved reducing this delay by devising an
implementation that tunnels. Rather than have the care-of-address change,
you fix it at an anchor router, and it forms a tunnel, passing the mobile's
packets to the router where the mobile is located. This router then delivers
the data packets to the mobile under the old care-of-address. At a pause in
the real time conversation (cellphone) or data traffic (mobile Internet
device), the router updates the care-of-address.
Thanks to Kempf and Wood's work, the wireless world may soon be less
glitchy. Kempf and Wood's work is currently being specified by the IETF
for the current version of IP (IPv4 ), and a variation is also being done
for IPv6.
Communities
Oracle Labs
