RE: GPRS Tunnel Protocol (GTP)

Hi, 

The problem you're trying to solve is essentially
that the "application" sets the filter on a default
router. You are essentially saying that the application
only sees a home address and the default router only
sees the CoA therefore the filter (TFT) will never
match the incoming/outgoing traffic. I'm not going
through the Go interface just the basic problem in
the absence of IMS. 

So there are two obvious alternatives for solving this:
- Make the UE use the right address in the PDP context setup
for the TFT. 
- Add a "MIP flag" in the message that sets up the TFT
(PDP context)and make the GGSN parse the packet to check for
the real addresses. 

In the first alternative, the MT's implementation could 
snoop the PDP context activation messages and get the 
IPv6 prefix that is allocated to the UE and replace the 
HoA in any messages that are sent to set the TFT with the CoA. 
However, this will clearly not work for the CN if it 
were also mobile because the MT could not possibly
know what the CN's CoA would be. 

The second bullet above would imply making the GGSN
aware of IPv6 headers and parse them to see if the 
HoA is included in the HAO (for route opt) or inside
the tunnel (when the packets are forwarded by the HA). 

I guess the immediate answer to the second solution is 
"this will increase the load on the GGSN". That's true, 
but increasing the load is not a general issue for any access 
router today, because none of them are _designed_ to handle 
an entire city. So, if you think that this will reduce the 
performance in the GGSN then I'd say use more GGSNs and make 
them have a smaller coverage area. 

IP networks are not generally designed in the way that 
the GPRS core network is designed. I.e. An access router 
is expected to serve a small number of customers. Therefore, 
you can afford to have complex filters in it. 

Hope this helps, 
Hesham