What's the benefit of L2 Triggers in 3G/Ad-Hoc systems ?

In general, it is a good idea to enhance the IP layer to include input from
L2 (I do not want to get into the issue of whether it has to be a standard
or just an implementation choice). However, the real benefit of changing IP 
routing based on L2 triggers is not clear for 3G systems. I would imagine it 
is more beneficial for the Ad-Hoc systems. 

Could one of the proponents of this issue refer me to any work that quantifies
the merit of such a scheme for 3G and/or Ad-Hoc systems?

For the 3G systems (CDMA2000/UMTS) you would most probably terminate the
IP connection at the PDSN/GGSN (more like HA in Mobile-IP) and then run
a PPP link to the Mobile. Now, handoffs are done much further away from
PDSN/GGSN and clearly, the latency is too much for us derive any benefit
from any L2 info. Even if you do have that info fast enough, you cannot
do much at IP layer since the Radio Access Network works some-what like a 
circuit. You do not perform any routing to the Mobile beyond the PDSN/GGSN. 
You just tunnel the PPP frames through GRE, GTP etc. 

In case of evolutions to 3G (1x-EV-DO, 1x-EV-DV and HSDPA)
you anyway have fast link adaptation and fast cell site selection. Both
of these work below the IP layer to maximize radio channel efficiency.
Again, the benefit of L2 triggers to IP is not clear. If you have a
100% IP based RAN where the base stations also have IP addresses, I can
see L2 triggers becoming more beneficial..again given the time-scales
(can be as small as 1-2ms), I doubt if there is any advantage in changing
the routing functionality that fast. It may just be best done at L1/L2 as 
is currently being done.

I am curious about any work performed in this area...

Thanks,
Kamesh

Phil Neumiller wrote:
> 
> 
> A more systemic question might be is IP mobility important to the Internet
> community?  Let's face it, mobile IP has seen scant deployment in its
> years of existence.  Why?  Obviously its missing thing that would make it
> commercially viable.  The 3G guys worked hard to add some of these,
> but 3G is not necessarily moving that fast.  The hot spot, WLAN, WPAN,
> ad hoc, mesh community is moving much faster.  There are many cheap
> radios available here and much more can be done with them quickly.
> L2 triggers are a win-win since they benefit 3G, 4G, WLAN, WPAN,
> mobileip, and MANETs.

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