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How to evaluate a DSL Service There are so many offerings out in the market that it
can be
really hard to compare what they offer. How can you
decide which
DSL service is right for you?
The key considerations are
a. Performance
b. Reliability
c. Support
d. Value Add
e. Cost
Key Considerations
a. Performance
To illustrate this we will use a 512/512kbps SDSL
(Symmetric Digital Subscriber Line) line as an example though the
points
apply to any service. View the explanatory diagram at
http://www.rosser.com.au/news/newsletter/Aug20042.htm
When you sign up for a service of a particular speed,
you expect
to get that speed but things may still run slowly. The first
point of congestion is the local loop. Based on our
example, if
you are trying to download at more than 512kbps or
upload at more
than 512 kbps then you will create congestion on the
line. Your
performance may also suffer from traffic that you
didn't generate
such as worm traffic, hacker probes, SPAM and denial
of service attacks. For all of these problems, your ISP is not
really to blame. Our Bandwidth Doctor Service can diagnose and
these
problems and recommend solutions.
http://www.rosser.com.au/solutions/bandwidthdoc.htm Where it gets interesting is looking at the next step
upstream.
Your line terminates in a DSLAM (DSL Access
Multiplexer ) in the
local exchange with many other services. From there
your ISP must
'back haul' all this traffic to their point of
aggregation (POA).
This backhaul costs money and every carrier will take
care not to
pay for more than they need. But how much is that? If they had
200 customers with a 512k service who all used their
link flat out
at the same time they'd need about 100Mb/s of backhaul
for that
exchange. That would be a 1:1 contention ratio and
very
expensive. The actual situation is very different. Most
customers hit 100% utilisation only for very short
periods &
average more like 5-8%during business hours. So a
service is
considered business grade if the contention ratio on
the back-haul is 20:1 or less. Actually, the better carriers don't
use a fixed
contention ratio, they monitor the utilisation of the
backhaul and
add bandwidth as needed to prevent congestion. For
example,
Request (now Powertel) and Comindico.
Stay away from
'residential
ADSL' where the backhaul contention ratio can reach
100:1 Does this mean that if you choose a
residential based
service you will
get what you've paid for? Not necessarily. Once the
data has been
hauled back to the carrier's main point of aggregation
(usually in
the nearest capital city) from all the exchanges in
the region, it
still has to get to 'the internet'. This is another
point of
possible congestion where ISPs can save money at your
expense. It
is relatively cheap for an ISP to buy their upstream
bandwidth 'by
the pipe', eg an unlimited 10Mb/s service where they
don't pay for
download. If their total customer base is paying for
a combined
throughput of 500Mb/s then, in the example, they've
oversubscribed
their bandwidth 50:1. This may be OK for residential
users who
aren't online often but will not be acceptable for
businesses.
Our SHDSL and Ethernet service does not get squeezed through a
pipe like this
- we pay for every megabyte which gives us priority
and we are
connected directly into their core internet at wire
speeds. It is important that business grade customers ask
questions to
check on both bottlenecks.
b. Reliability
Although reliability has improved enormously there are
still
outages and there are differences between carriers. To assess
this you need to know who owns and manages the DSLAM
and whose
infrastructure you are traversing. Carriers such as
Powertel and XYZ (Optus) have a better track record
of uptime
and better service guarantees that suit business
connections.
c. Support
Check Service Level agreements & availability of
support to
trouble shoot your service. Do you need your routers
managed?
Under maintenance? What do you do if your router dies?
d. Value Add
Apart from the above, what features should you
consider?
Powertel exchanges can handle symmetric services-
something
essential for offices running VPN & ecommerce. can
your current
service provider do this? Is Voice over DSL something
your
business may need? Is traffic prioritisation
necessary?
e. Cost
In summary, you get what you pay for. Cheaper
bandwidth usually
means inferior bandwidth that may cause time sensitive
traffic to
suffer. Also, costs are falling so don't sign
contracts for
more than 12 months and review you carrier regularly.
However, if
you are on an private IP network, consider a 2 year
contract
minimum otherwise the initial costs of the hardware
and
installation is too high for only 12 months use & to
return a
significant ROI. |