Rails Beacon

Hi All,
   Hope am having a new idea for discussion. We can call it 'Rails
Beacon'.
   Rails provide immortal sessions, they don't expire unless we handle
it manually. Some sites handle this by closing the session after a fixed
time interval from the last server access, some others keep the session
until the user logs out. Both of these methods have their on
limitations. First one will close the session after a fixed interval
even if the user is on-line, it may also keep the session alive for a
long time even after the actual user log-out. The second method will
fail if the user fails to log-out. Hence Rails Beacon!...
   In this new technique the client will send a beacon signal to the
server and keep it updated about the client status. It must be send
continuously via an ajax request, windowed by a fixed time interval. If
the signal is not received within the specific time, server can trigger
session closure.

This technique have the following advantages:
1. The session is not closed when the client is on-line.
2. Session ends even if the user close the application without logging
out.
3. Server can detect client browser crashes and trigger session closure.
4. The time interval can be decreased for faster response.
5. The programmer can implement normal log-out mechanism.

Disadvantage:
1. Response time of the system is inversely proportional to the network
load crated by ajax query.

Kindly drop in your comments...