Re: [manet] I-D Action: draft-ietf-manet-dlep-latency-extension-01.txt

[Rick Taylor <[e-mail]>]

Hi Lou, Bow-Nan.

Thanks for doing this work, but I have a concern, but it might indicate
a lack of understanding of your intentions for this extension.

From my perspective, DLEP provides "near realtime" information about
the state of links between destinations, so for example if the latency
of the link changes, the updated latency metric is reported in a
Destination Update message from modem to router.

If your intention with this draft is to supply a mechanism to allow a
modem to report a rapidly fluctuating link latency (more than once per
second) at a lower rate, i.e. "This link is flapping fast between X and
Y ms" and report this every second with different X and Y, then I see
the point (although I don't want to use that modem).

If your intention with this draft is to supply a mechanism to allow a
modem to report a min and max latency for the link *once* (or very
infrequently) at Destination Up, then I oppose it.  If this is the case
I would suggest that the modem reporting Latency when it is known, and
the router recording the min and max as it is reported is how DLEP was
designed to be used.

My other query, which I raised at the mic in Chicago, was why this
extension only covers Latency.  Lou's response was that if people want
the same functionality for a different metric, a new extension can be
written.  I however suggest that it might be simpler to generalize the
data item in this extension to something like:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Data Item Type (TBD2)         | Length                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Metric Data Item Type (this DI type of the metric min/max)    :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Maximum Value                          :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                        Maximum Value (if 64bit)               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        Minimum Value                          :
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      :                        Minimum Value (if 64bit)               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The advantage of doing it this way would be that any metrics in future
extensions could immediately have a "Min/Max" extension data item.

Cheers,

Rick