We rarely use CIR. We will sometimes give business-class customers a
little bit of CIR so their VPN won't break, etc.
We aim for a minimum 6X on every customer, but we will occasionally
accept a borderline 4X-6X SM link because sometimes there's no choice. A
little degradation causing those links to sit at 4X during Netflix time
really drags the sectors down. So, I think it would be beneficial to
dynamically penalize the lower modulation SMs instead of letting them
sit there and eat up all the air time.
My $0.02.
On 11/13/2015 10:04 AM, Aaron Schneider wrote:
The Canopy scheduler operates with a combined priority based scheme and a round
robin based scheme. As has been covered here in the past, the scheduling
priority is as follows: 1) High Priority CIR 2) Low Priority CIR 3)
Bcast/Mcast CIR 4) High Priority 5) Low Priority 6) Bcast/Mcast.
If you don't oversubscribe your CIR, then things are fine. But, that is very
tricky when you assume CIR based on one data rate (say 8x), and the actual link
requiring that CIR is different (say 4x). Now, that SM is requiring twice as
much frame time to meet that CIR as you may have planned. This goes to the
concept of allocating capacity based on throughput, and it is generally how
Canopy works. The round robin comes in so that one SM can't take everything on
its own, it will try to be fairer, but, it will still do everything it can to
honor the CIRs of each SM in every frame.
We do have a feature in the works where we flip that a bit where the CIR
becomes airtime based so generally speaking, you are guaranteeing air time and
not throughput. The idea is that you will assign a CIR based on a given rate,
say 8x, and if the SM drops (or can only ever achieve) 4x, then they will get
half the data rate because they are only allowed the same amount of time as if
they were 8x. The underlying concept is easy, it is the external interface and
making it easily understood and helping you stay out of trouble with
configurations that is difficult. If it is OK to just say turn on the
option, but then not be able to predict the throughput, that's one thing, but
if you have a customer that needs a given throughput no matter what his data
rate becomes, and other customers that are OK with just having limited airtime
access, then the overall planning of CIR becomes tricky to not over-commit.
So what would you all prefer? An option per sector to enforce CIR in a given
way for all SMs? Or enforce CIR in a selectable way (throughput vs. air time)
per individual SMs on a given sector?
Regards,
-Aaron
