Re: Two-octet bandwidth values

[Qingming Ma <qma@cisco.com>]

At 05:15 PM 3/26/01 -0800, Bora Akyol wrote:

>On Sunday, March 25, 2001, at 08:05 PM, Kireeti Kompella wrote:
>
>>Let's get the ball rolling.  Please send questions and comments to the
>>list.  Here are mine:
>>
>>Questions to vendors:
>>1) Is floating point arithmetic a burdensome requirement?  Is having
>>    a new library of functions for the two-octet "floating point"
>>    representation a burdensome requirement?
>
>I don't see what exactly is wrong with the present approach, we have no 
>problem working with the present TE TLVs and no problems with floating point.

No one said the present approach is wrong. The problem you will soon
use out all sub-TLLV space in ISIS for further extensions. You can work
with the  present  TE TLVs,  if there is enough sub-TLV space.


>>2) Is halving the size of the bandwidth TLVs a big win (keep in mind
>>    that more bandwidth TLVs are being proposed)?
>>    (a) for ISIS?
>>    (b) for OSPF?
>>    (c) if the answers for ISIS and OSPF differ, is it acceptable to
>>        have different formats for the two protocols?
>
>I think it is unacceptable to have OSPF and ISIS TE TLVs differ. I think 
>halving the size of the bandwidth TLVs is not very useful. It causes yet 
>another "transition" problem just as people are getting used to the 
>present scheme.

Again, it may not be very useful, if there is sufficient sub-TLV space.



>>Questions to vendors & carriers:
>>1) Is 10 bits of dynamic range (0.1% accuracy) good enough?
>This depends a lot on the bandwidth, on an OC768c this will translate to a 
>whopping 400 Mbps, which to me is inadequate.  Our routers also support 
>bundled links which we call "Bonds" that can achieve bandwidths much 
>larger than 40 Gbps. So my answer to 10 bits of dynamic range is NO.

First, you did not do your Math correct. If you have bandwidth
value as large as OC768c, the accuracy can be at 67 Mbps
level, rather than 400 Mbps. When you use the bandwidth value
to select a path, I don't think you need to worry about the bandwidth
value 67 Mbps more or less if the link has available bandwidth
at 40 Gbps level.


>>2) Are you in favor of this draft, or against?
>
>Seems like we have more important stuff to focus on then this particular 
>topic.
>
>Bora