Hi Julien, WG,
Yes, the draft-ietf-roll-routing-metrics-03 suggests that the
metrics may
exceed 255 bytes, and so the DIO suboption for DAG Metric Container
drives
the overall requirements for suboption length.
If we use 16bits for length, maybe 1 byte is `wasted' to specify a
short ( <
255 bytes) option.
If we use 8bits for length in units of 8bytes, only one byte is used
for
suboption length in all cases, so the second byte is saved. But the
suboption itself must pad for [0-7] bytes to meet the 8 byte
boundary. In
the first case, 0 byte of padding is required, one byte is saved from
encoding the suboption length, and one byte is saved overall. In
the second
case, 1 byte of padding is used and one byte is saved from the
suboption
length, breaking even. In the 6 other cases, more bytes are used for
padding than are saved in encoding the suboption length.
We don't know anything yet about a typical distribution of lengths for
suboptions, in particular the DAG Metric Container. So perhaps this
discussion could be premature. But, given that in the 8byte
encoding case
we use more bytes in 6/8 of the possible cases, my opinion is that
it is
better to stick with a 16-bit suboption length in units of bytes.
Thoughts?
Did you have another architectural driver in mind?
-Tim
Julien Abeille (jabeille) wrote:
Hi all,
do we expect DIO suboptions to be longer than 255 bytes? if yes
would it
be ok to spell the length in multiple of 8bytes instead of bytes
(value
of 1 means 8 bytes, like in ND). The target is to use 8 bits
instead of 16.
Thank you,
Julien
------------------------------------------------------------------------
_______________________________________________
Roll mailing list
Roll at ietf.org
https://www.ietf.org/mailman/listinfo/roll
_______________________________________________
Roll mailing list
Roll at ietf.org
https://www.ietf.org/mailman/listinfo/roll
