Re: [manet] draft-ietf-manet-nhdp-10.txt - WGLC - Oct 5th 2009

["Dearlove, Christopher (UK)" <Chris.Dearlove at baesystems.com>]

First, my apologies, I'm going to just drop a couple of comments,
then won't see any responses for a week.

> Metrics are not currently part of NHDP the way you might be thinking.
There
> are up threshold/metric concepts along with state machines which
dictate
> behavior with regard to these and bringing links up and down but there
is no
> prebuilt way for calculating these link metrics.  I believe that
OLSRv2 will
> have some method of doing this (easily done on a two hop basis with
> packetbb/NHDP methods)

See the latest version of draft-dearlove-olsrv2-metrics for how
we are planning to add metrics to OLSRv2, including to HELLO
messages. Fundamentally we report direct and best metrics to an
address, the latter possibly using another link. But this is
OLSRv2, not NHDP. Other users of MHDP may not need metrics, and
thus should not be burdened with them.

We are working on the addrssing issue. Basically, without the
need for on the wire interface IDs, as long as a router can map
a HELLO message to the corresponding Interface Information
Base (which may use an interface ID, but NHDP doesn't need to get
into that detail, it just needs the concept I just mentioned)
then duplicate addresses on different interface are possible
IF messages from these interfaces cannot be received by the same
neighbour interface. This is the case in Stan's example, and is
the case for e.g. a node with two 802.11 interfaces (and possibly
Ethernet interfaces also) if the 802.11 interfaces use different
channels. This I think gets the gain in the cases of real interest
without added complexity and bandwidth.

With regard to how many addresses to advertise, there is an NHDP
and an OLSRv2 answer. For pure NHDP use, each interface needs
at least one address, and also to report any address that it may
use as the source address of an IP datagram carrying NHDP information.
(In practice you can probably ensure the same address is always used.)
For OLSRv2 use that needs to be extended to also include any addresses
the router wants to make globally available as a destination. (Stronger
requirements, that result in added information, is explicitly noted
as permitted, it has to be in order to build e.g. OLSRv2 or SMF.)

Fundamentally, all that needs to change in NHDP is
- A relaxation of address reuse, but with the important caveat above.
- A relaxation of required address inclusion, with the condition
  noted above.

(There are of course details to get right, as ever.)

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