Capacity planning , transit vs last mile

Blake Hudson blake at
Fri Apr 1 14:32:04 UTC 2016

Jean-Francois Mezei wrote on 4/1/2016 1:38 AM:
> My question has to do with how does one determine that theshold where
> you start to get more chaotic patterns and need more  capacity per
> customer than if you had over 1000 customers ?
> My goal is to suggest some standard to prevent gross underprovisioning
> by ISPs who win subsidies to deploy in a region.
>  From what I am reading, the old standard (contention ratio of 50:1 for
> residential service) is no longer valid as a single metric especially
> for smaller deployments with higher speeds.
While the formula provided by Baldur may very well be accurate, it 
allows projections on several data points (advertised speed, average per 
customer speed, customer counts, customers online @ peak) which may or 
may not turn out to be accurate or could be fudged to create misleading 
estimates. I think a simpler projection, taking harder numbers into 
account may be easier to implement as a requirement and less likely to 
be gained by someone. I think it would be sufficient to simply specify a 
minimum Mbps bound per customer (aka a committed information rate) for a 
network build. As you and others have stated, typical current use is 
currently ~1-2Mbps per household/customer. If we forecast growth to be 
30% per year, a 10 year build might anticipate using a last mile 
technology capable of providing ~13Mbps CIR [using the compound interest 
formula where A = 1Mbps * (1 + 0.3)^10years ] in 10 years time. This 
projection uses growth, which has historical precedent, and current 
usage, which you indicate is already being measured and reported. 
Something that is less static would be the technology improvements. An 
operator might be able to assume gpon now and 10G-pon in a few years (or 
DOCSIS 3.0 -> 3.1), to meet future requirements.

Regarding your question about how such a formula might scale, especially 
on the small end. I think it's a valid concern. This could be measured 
in today's rural HFC networks or wireless network where it may be common 
to have fewer than 50 customers sharing a 40Mbps-100Mbps access media. I 
think you'll find that at this small a scale, the 1-2Mbps per customer 
number probably still holds true. You obviously won't be able to sell 
1000Mbps service (or even 100Mbps) to these customers, given the access 
media limitations. This could be addressed elsewhere in your 
requirements. For example, if it were required that operators "...offer 
services capable of delivering 100Mbps service to each end user with a 
CIR derived from table A", the operator would be forced to provide a 
100Mbps+ pipe even if it were only serving 10 customers on that pipe 
that see ~ 20Mbps aggregate peak period usage today. That 80Mbps of 
overhead is not wasted, it's intentionally there for your users' future 
needs and to provide burst capacity. A smart operator would probably 
avoid such cases and attempt to aggregate users in ways that minimize 
expense and make the most of the access technology.


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