Capacity planning , transit vs last mile

Baldur Norddahl baldur.norddahl at
Fri Apr 1 08:07:00 UTC 2016


40 Mbps is plenty fast that even a family will not be using much more data
with higher speed. So that transit argument is a poor excuse.

A formula could be:

 [max speed sold to customers] * 2 + [number of customers] * [average peak

The number 2 in the above is not well researched but I would expect it to
be in that ballpark.

The [average peak number] is 2 Mbps for our network. Others seem to claim
they get away with only 1 Mbps, but our users are doing 2 Mbps for sure. I
believe this is probably because we have many families. It does matter when
each customer is really a family of 5 compared to one single person.

The formula holds up for both few and large number of users. With few users
the left side of the formula dominates and with many users it is the right



On 1 April 2016 at 08:38, Jean-Francois Mezei <jfmezei_nanog at>

> On 2016-03-31 19:38, Baldur Norddahl wrote:
> > You will find that total data download per month is unrelated to service
> > speed except for very slow service.
> Yep. Netflix still takes 7mbps even if you are on a 1gbps service.
> However, with families, higher speed allow more family members to be
> active at same time and this could begin to have visible impact (if not
> already).
> Note that a rural coop deployed FTTP for their territory, but only offer
> 40mbps max subscription because they can't afford the transit from the
> single incumbent who offers transit in their region. So I assume that
> with under 1000, service speed starts to matter when sizing the transit
> capacity.
> > If you have too few users the pattern becomes chaotic.
> 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 residential service) is no longer valid as a single metric especially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.
> For the last mile, GPON is easy as it is essentually 32 homes per GPON
> link. For cable, the CRTC would have its own numbers for number of homes
> per node. (BTW, Australia's NBN V2.0 plans to have 600 homes per node
> since they don't have budget to split nodes).
> But for fixed wireless and satellite, there needs to be some standard to
> provent gross oversubscription.
> Say you have a fixed wirelss tower with enough spectrum to broadcast
> 40mbps. How do you calculate how many customers at average speed of
> 15mbps can comfortably fit on this antenna ?
> I realise existing ISPs use monthly statistics of 95th percentile to see
> how much capacity is used and whether the link has reached saturation
> and there should be s stop sell or get more spectrum.
> But from a regulatory point of view, in evaluating a bid to serve a
> region, the regulator would need rules to establish whether the bidder
> will be able to serve the population with whatever solution the bidder
> proposes.
> Does the FCC have any such rules in the USA, or are its broadband
> deployment subsidies only based on the ISP marketing speeds that meet
> the FCC's  definition of "broadband" ? (and no concern about whether
> those will be delivered or not).

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