Here's how I read that Don (and someone else correct me if I'm wrong)
Every 5 minutes, they add up all the data transferred over that time period, and divide by 300 to
get your rate in bits/second. They do this for both in and out traffic separately. In a 30 day
month, there will be 8640 samples (30 days x 24hrs/day x 12 samples per hour). Then they arrange
these samples in order, and lop off the top 432 samples, or 5%. The largest sample left is
considered your usage in one direction. They do this for both inbound and outbound separately, then
take the largest of those two to get your usage. So if your inbound rate after all this is only .4
mbit/sec but your outbound rate is measured at 1.0 mbit/sec, you're going to get charged for 1
What I think this means for you is that if you pay for a 512 kbit/sec transfer rate and exceed 512
kbit/sec (not the 768k burst rate) more than about 5% of the time, you're going to get charged an
overage fee. Mathematically for the month, you could average out way below 512kbit/sec rate
overall, but still have to pay overage fees since for 5% of the samples you were over that rate.
From what I understand, this is a relatively typical scheme with burstable connections.
If I were you, I'd set the traffic shaper at the 512k level and leave it. If you hit the 768k hard
limit for more than 5% of the time (5% of the samples actually, which is really about 36 hours a
month), you'd be paying about $60 in overage fees for that month.
From: Don Munyak [mailto:don dot munyak at gmail dot com]
Sent: Thu 6/29/2006 10:21 AM
To: m0n0wall at lists dot m0n0 dot ch
Subject: [m0n0wall] Taffic Shapping Question
Taffic Shapping Question
This may be a bit off topic, but I'm a little confused and/or don't
understand. In the proposal were are considering for a co-lo facility,
the vendor has made the following two statements about the measureable
bandwidth plan. I've read it a hundred times and still don't quite
understand HOW-to interpret.
- Industry standard 21 RU w/ 19" W x 28" D x 36" H usable space.
- (1) CAT 6 Ethernet data connections (upgradeable to gigabit Ethernet)
- (1) DSO/DS1 connections
- (1) Single 100Mbps Ethernet drop
Bandwidth Rate Plan: Single 100Mbps Ethernet drop with data transfer
measured at 95th percentile of maximum transfer rate per month.
Commitment is 1.0 Mbps, overage charged at $30.00 per 0.1Mbps.
Internet Bandwidth: single 100 Mbps Ethernet connection, 1 Mbps
commitment on burstable 95th percentile billing.
1) Burstable Bandwidth measured in Mbps using 95th percentile calculation.
Burstable Front Channel connectivity bandwidth subscription levels are
in increments of 1 Mbps. The minimum bandwidth subscription levels per
rack are as follows:
Cabinet or Shared Cage | Half-Rack (8 Amps Max) | 0.5 Mbps
Cabinet or Shared Cage | Full-Rack (16 Amps Max) | 1.0 Mbps
95th Percentile Burstable Bandwidth Measurement calculation:
bayMountain collects the number of bits (in both octets in and octets
out) in 5-minute intervals. The number of bits is then divided by 300
seconds (5 minutes x 60 seconds) to derive one Inbound sample and one
Outbound sample. The total monthly sample size will then be sorted in
descending order (from largest to smallest) in two separate groups
(Inbound and Outbound). The top 5% of the sample size (roughly 432 of
the top ranked samples) is removed. The next highest sample after the
removal of top 5% is the 95th percentile sustained usage level for the
month. The highest 95th percentile sample between the Inbound and
Outbound samples is considered the sustained usage level for billing
purposes. Overages to be billed in 0.1 Mbps increments.
With respect to m0n0wall, is this saying (using an arbitary number) if
I have paid for a 512k feed burstable to 768k, but I keep exceeding
768k, I'm going to get charged overage ? If so, I should consider
using traffic shapper to limit burstable / sustained traffic ??
Also....Would someone please translate the "Burstable Bandwidth"
explanation into laymans terms. Maybe providing an example.
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