Subject: [Mip6] Testing Binding Latency with Return Routability and Home Binding

From: Gregory Daley <[email-masked]>
Date: Thu, 13 Nov 2003 17:15:26 +1100

I hope this is not just saying the obvious now 
after Jari's mail posting, but I'd started before
I read his post (so I think I'll continue anyway).

If this contributes to the RO hints document, 
then that would be good.

According to MIPv6, the host which wants to do RO MUST
first perform Return Routability by sending HoTI and CoTI
messages to the CN.

The CoTI message has a source of the MN's CoA and is sent
directly, without MIPv6 tunneling to the CN.   The CN
responds to this packet by sending directly to the MN
solicits a response packet called a CoT,
which contains a cookie.
A message called the Home Test Initiation (HoTI) is reverse
tunnelled by the MN to its HA.  When this is sent to a CN,
the CN responds with a Home Test (HoT) sent to the MN's
Home Address.   This packet is therefore tunnelled to the 
MN.

Binding signalling is performed with the sequence of CoTI/CoT
exchange and then sending a BU to the CN, containing a cookie
formed from data in the CoT and HoT.  

The binding latency therefore is approximately 1.5 * RTT of the
CoTI/CoT exchange (The CoT/I RTT is represented as R).

Similarly, the binding latency for Home Agent Bindings is 
measurable using the delay before receiving the binding Ack
(This latency is represented by B)

The time for packets to home tunneled to the CN to 
round trip may be checked using the HOT/I exchange (This latency
is represented as H).

   If  H is < min [ maximum acceptable RTTs for MN-CN comms] 

       AND 

       (0.5 * B) < (1.5 * R)  

Then performing RO may not be necessary.

In this case, the latency is sufficiently low, and the 
packet loss from reverse tunneling through the HA
is lower than from using Route optimization.

This assumes similar latency for the uplink as the downlink.

Also, increased RTT for packets on the home tunneled
link may cause feedback for upper protocol layers.
If this degrades performance, it may be sufficient to
override this decision and use RO anyway.
 
While there may be some variation in the RTT numbers
retrieved by measuring HoT/I CoT/I and BU/BAck,
These numbers can be considered indicative if the 
MN moves locally within a domain.

Periodic re-probing with CoT/I and HoT/I at rates
described in MIPv6, and measuring BU/BAck latency
at re-binding may be sufficient to provide 
updated information about these delays.

Of course there is a lot of guesstimation in this, 
but it seems fairly simple.

_______________________________________________
Mip6 mailing list
[email-masked]
https://www.ietf.org/mailman/listinfo/mip6