Information Technology Reference
In-Depth Information
and S2 will continue on its own—until L1 or L2 moves. In particu
lar, suppose L1 moves toward S2. For awhile it will continue to
hear just S1's beacon, but after some time it will hear S2's beacon as
well. If the connection with S1 seems effective—that is, if the signal
from S1 is strong—L1 may ignore S2 and continue to communicate
with S1. However, at some point, S1's signal may become rather
weak, and reliability may prompt L1 to interact with S2. In order to
switch its stationary computer from S1 to S2, L1 could drop its con
nection with S1 (with a
dissociation
message), but this would cause
a loss of continuity for the user. For example, suppose you were
shopping on the Web for topics, and you had placed some titles into
your shopping cart. You would want that session to continue no
matter where you moved with your laptop L1, but switching to S2
with a new association request would break that continuity.
Instead, L1 can send a
reassociation
message to S2. This pro
vides the same authentication function as an association request,
but it also specifies that current work is being done through access
point S1. After S2 replies with appropriate information for a new
connection, then S2 can contact S1 about any information pending
for L1. For example, information on a new book title might have
arrived from the online bookstore while L1 was conversing with S1
and S2. This information can then be relayed to S2. Also, because
your initial contact with the bookstore was made through S1, that
connection can remain for continuity, and information can be for
warded to S2 as needed.
As you move around with L1, perhaps to a new access point S3,
your reassociation message to S3 will allow it to retrieve pending
information from S2 and then to inform S1 that further data need
not go to S2 but rather to S3. Altogether, association requests allow
a mobile computer to establish a link to the Internet, while reasso
ciation requests allow access points to forward current information
to whatever access point might be involved with the current com
munications.
From a user's perspective, you can move your laptop L1 from
one place to another to another without worrying just what access
point is nearby. As long as your computer can connect with some
access point in the network, then the sequence of reassociation re
quests can allow machines in a network to perform the administra
tion necessary to maintain Internet links you may have established
throughout your travels.
