Subject: [mobile-ip] Low Latency Issue: Should HTT be MUST, SHOULD, or MAY?

From: James Kempf <[email-masked]>
Date: Thu, 30 Aug 2001 10:25:57 -0700 (PDT)

At IETF 51 in London, it was agreed to add the Handoff To Third (HTT)
to the POST-REGISTRATION part of the MIPv4 low latency handoff design.
The HTT allows a MN that is already receiving traffic via a tunnel
from an anchor FA to move to a new FA without receiving a new CoA.
It is necessary because the current design provides no support for
the case where a MN is moving so rapidly that it does not complete
L3 handover by the time it moves to a new FA. 

The authors of the draft have discussed this, and are not in agreement
about what level to incorporate HTT. In particular, should HTT be
MUST, SHOULD, or MAY?

In favor of MAY: We should keep the protocol as simple as possible.
This message is only required in certain restricted circumstances
that will not occur for every radio link protocol, and therefore
it should not be required unless the radio link protocol supports
rapid movement to a new FA.

In favor of MUST: In addition to fixing the abovementioned bug,
HTT also provides a new capability that is not available in
RFC 2002 nor with PRE-REGISTRATION, namely the ability of the MN
to choose when it should obtain a CoA based upon its traffic.
If the MN is receiving real time traffic, it may choose to
forgo L3 handoff until the real time stream is done, thereby 
avoiding the radio link traffic involved in MIP signalling. This
is similar to the BETH proposal for IPv6, which the WG agreed
to incorporate into the FMIPv6 draft.

The authors need working group guidance on this issue. 

		jak

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From: Sebastian Thalanany <[email-masked]>
Date: Fri, 31 Aug 2001 08:42:09 -0500

Hello James,

                            Perhaps the following paragraph, indicating
the context in which HTT is
applied, may support the use of "MUST".

                            "In case the link layer triggers, which are
required by the post-registration scheme,
to support the movement of the wireless end of the BET, are available,
then the HTT scheme
MUST be applied to avoid a context transfer from the aFA to the nFA for
delay-sensitive information."

Regards,
     Sebastian