Dear All,
Availability is one measure of quality used in Service Level Agreement
programs by telecommunication providers today. The way availablity is
measured by vendors determines the compensation customers receive for
service outages and determines how good the guarantee is. The way the
measures are done today is via time series, i.e. measure availability
over time. This doesn't take into account the network size. The only
way to take into account network size is to measure availability
across the network. Doing so provides compensation based on the amount
of the network that was not available. Please see below for a
complete, but concise, summary of what the different availability
measures actually guarantee! Thanks
Measures of Availability
Availability of service is measured today using time series data by
all vendors in the telecommunications industry, for all their
services. Cross section data is not used today to measure
availability. But cross section data is very useful in quantifying a
customer's network availability.
The difference between the times series data and cross section data is:
1. Times series measures the availability of an individual IP-VPN
site, Frame/ATM port or pvc, or Private line circuit over time.
2. Cross section data measures the availability of an IP-VPN
Network, Frame/ATM Network or Private Line Network at a point in time.
In other words:
1. Time series measures Site Availability, Port Availability, PVC
Availability, or Circuit Availability for IP-VPN, Frame/ATM and
Private Line service respectively. These measures are used in SLA
programs today.
2. Cross section data measures Network Availability for a IP-VPN
Network, Frame/ATM Network or Private Line Network. These measures are
not used in SLA programs today. (The name "Network Availability" is
used to describe availability measures by some vendors in their SLA
programs. But the measurement is a time series measure, a measure of
availability on a site, port or pvc over time, not a measure across
the network.) The cross section approach is a patent pending
methodology of L. Swanzer - E2E SLA Support, LLC. Their use requires
license be obtained by the telecommunications providers to offer these
metrics to their customers.
The difference between a time series measure of availability and a
cross section measure of availability is shown in the table below
(please see www.e2eslasupport.com if you can not read the table. This
memo is on our website). The time series approach measures the
availability of each IP-VPN Site (it could also be a Frame/ATM port or
pvc, or a Private Line circuit) for any given month. So for example,
sites 1, 2 and sites 6-10 had 100% availability in January. Sites 3, 4
and 5 had 99.03% availability in January. Sites 3, 4 and 5 had a 7
hour outage, from 2pm-9pm on January 15th, which implies 99.03%
availability.
Jan Jan Jan Jan
Sites 1/1-1/15 1/15 1/15-1/31 Site Avail. %Sites
Site 1 100% 100% 100% 100% 10%
Site 2 100% 100% 100% 100% 10%
Site 3 100% 0% 100% 99.03% 10%
Site 4 100% 0% 100% 99.03% 10%
Site 5 100% 0% 100% 99.03% 10%
Site 6 100% 100% 100% 100% 10%
Site 7 100% 100% 100% 100% 10%
Site 8 100% 100% 100% 100% 10%
Site 9 100% 100% 100% 100% 10%
Site 10 100% 100% 100% 100% 10%
Total 100% 70% 100% 99.71% 100%
Percent
Time in 48.39% 0.97% 50.64% 100%
Range
The cross section approach measures availability of the network at
various points in time. From January 1st to January 15th, there were
no outages on the network. Therefore the network had 100% availability
during those first 15 days of the month. On January 15th, from 2pm to
9pm, sites 3, 4 and 5 had 0% availability (these sites were affected
by a seven hour outage). Therefore, from 2pm-9pm, on January 15th, the
network availability was 70%.
Average availability is sometimes used as the SLA metric for
availability. The average availability is the same whether the measure
of availability is Network Availability or Site Availability. The
method used to calculate average availability today is by averaging
the individual Site Availabilities. The average availability measures
are a weighted average. With Network Availability the weights are the
time spent at different ranges of availability, with Site Availability
(used today) the weights are the percent of Sites with different
levels of availability. The Average Availability, in this case, was
99.71% shown in the bottom right corner.
Network Availability, Site Availability and Average Availability all
have their own strengths and weaknesses.
The weakness with Network Availability is that compensation is capped
by the amount of time the network is below the target level of
availability. So, if 50% of the network is down for a couple of hours
then the most the customer can be credited is the percent of time the
network was down. For a 2 hour outage this amounts to .28% (2 hours
out of 720 total hours in the month) of the total network
charges. Even if the entire network is down, the credit is capped by
the percent time the network was down. So if 100% of the network is
down for 2 hours the maximum compensation due the customer is .28% of
the network charges. On the other hand, Site Availability provides
compensation based on the percent of the sites that are down. So if
50% or 100% of the Sites were down for 2 hours Site Availability would
compensate a customer up to 50% or 100% of the network charges,
respectively.
The weakness of Site Availability is that compensation is capped by
the percent of sites that are below the target level of
availability. For example, if there were a problem, in a given month,
where a site had recurring problems that lasted much of the month, the
customer's compensation would be capped to be a maximum of the charges
on the problem site. For a large network, say a network with 100
sites, this would amount to a 1% of the total network charges are
eligible for credit. If, on the other hand, Network Availability were
the measure of availability, then the customer would be eligible for
up to a maximum of 100% of the network charges, if the site caused the
network to be below the target level for the entire month.
In general, Site Availability is going to compensate better then
Network Availability when outages are of relatively short duration and
impact many sites all at the same time. Network Availability will
provide more compensation to the customer in months when outages are
sporadic, occurring at different points and time during month.
Finally, Average Availability is an all or nothing deal. It provides
either the best compensation or the worse compensation of the three
metrics, depending on the outages. With Average Availability
compensation is not limited by the amount of time the network is below
the target level of availability nor is it limited by the percent of
sites that are below a targeted level of availability. If the Average
Availability target is missed the customer is eligible for
compensation for all the network charges.
The issue with Average Availability is that it won't provide any
compensation at all if the target is met, even though there could have
been outages on the network that required compensation under Network
Availability and/or Site Availability. If the target for Average
Availability is 99.99% then a network wide outage that last 4 minutes
and 31 seconds would not be eligible for any compensation. Similarly
an outage that lasts 72 hours at a single site, on a network with 1000
sites, would not be eligible for any compensation. In both cases, the
4 minute 31second network wide outage and the 72 outage on a single
site, would meet a 99.99% average availability target.
None of the availability measures protect the customer against all
types of outages. For complete coverage against any type of outage you
may consider combining Site Availability and Network Availability. For
example, include both measures of availability in the Service Level
Agreements. The measure that applies in any given month is the metric
that provides the most compensation to the customer. Another way of
getting the benefit of Site and Network Availability is to multiply
the percent of the time of the month a particular outage lasted by the
percent of total sites effected. The result would be the total
percentage of the network that was affected by the outage: Percent
time of the month * Percent of Circuits. Applying the resulting
percentage to total network charges would amount to a refund of the
customer's charges for the effected circuits, for the time the
circuits were down. Of course an additional percent credit would have
to be added to compensate the customer for the burden of the outage.
This is a very brief summary of today's measures of availability. We
have a detailed presentation, which you can view from our website. You
can also find out more about our: SLA administration services
(tracking, reporting, claim processing), consulting services,
presentations, and other services. Please see www.e2eslasupport.com
for more information.
Network Availability and the variants of it are patent pending
business methodologies of L. Swanzer and E2E SLA Support, LLC.
Thank you,
Larry Swanzer
E2E SLA Support, LLC
908-806-4097
slasupport (lswanzer.slasupport@earthlink.net)