The WISP Approach
Visions of license-free,
monopoly-shattering, high-bandwidth networks are certainly dancing
through the heads of some business-minded individuals these days. On
the surface, it looks like sound reasoning: if people are conditioned
into believing that 6Mb DSL costs $250 per month to provide, then
they'll certainly be willing to pay at least that
much for an 11Mb wireless connection that costs pennies to operate,
particularly if it's cleverly packaged as an upgrade
to a brand name they already know. The temptation of high profits and
low operating costs seems to have once again allowed marketing to
give way to good sense. Thus, the
"Wireless DSL" phenomenon
was born. (Who needs an actual technology when you can market an
acronym, anyway?)
In practice, many WISPs are finding out that it's not as simple
as throwing some antennas up and raking in the cash. To start with,
true DSL provides a full-duplex, switched line. Most DSL lines are
asymmetric, meaning that they allow for a higher download speed at
the expense of slower upload speed. This difference is hardly
noticeable when most of the network traffic is incoming (i.e., when
users are browsing the web), but it is present. Even with the
low-speed upload limitation, a full-duplex line can still upload and
download data simultaneously. Would-be wireless
providers that build on consumer-grade wireless technology are
limited to half-duplex, shared bandwidth connections. That means that
to actually provide the same quality of service as a wired DSL line,
they would need four radios for each customer: two at each end, using
one for upstream and one for downstream service. If the network
infrastructure plan is to provide a few (or even a few dozen)
wireless access sites throughout a city, these would need to be
shared between all of the users, further degrading network
performance, much like the cable modem nightmare. Additional access
sites could help, but adding equipment also adds to hardware and
operating costs.
Speaking of access
points, where exactly should they be placed? Naturally, the antennas
should be located wherever the greatest expected customer base can
see them. Unless you've tried it, I guarantee this
is trickier than it sounds. Trees, metal buildings, chain-link
fences, and the natural lay of the land make antenna placement an
interesting challenge for a hobbyist, but a nightmare for a network
engineer. As we'll see later, an antenna site at
least needs power and a sturdy mast to mount equipment on, and,
preferably, it also has access to a wired backbone. Otherwise, even
more radio gear is needed to provide network service to the tower.
Suppose that marketing has sufficiently duped would-be customers and
claims to have enough tower sites to make offering network services
at least a possibility. Now imagine that a prospective customer
actually calls, requesting service. How does the WISP know if service
is possible? With DSL, it's straightforward: look up
the customer's phone number in the central database,
figure out about how far they are from the CO, and give them an
estimate. Unfortunately, no known database can tell you for certain
what a given address has line of sight to.
As we'll see later,
topographical
software can help perform some preliminary work to help rule out the
definite impossibilities. Some topographical packages even include
tree and ground clutter data, although these tend to be considerably
more expensive (and of dubious real value, unless they are
up-to-date). Using such software, we might even be able to upgrade
the potential customer to a
"maybe." Ultimately, however, the
only way to know if a particular customer can reach the
WISP's backbone over wireless is to send out a tech
with test gear, and try it.
So now the poor WISP must be prepared to "roll a
truck" for new installations, making on-site calls
to people who aren't even customers yet. If
they're lucky, technicians might even get a test
shot to work. At this point, finally, equipment can be installed,
contracts signed, and the customer can get online at something almost
resembling DSL. That is, be online until a bird perches on the
antenna, or a new building goes up in the link path, or the leaves
come out in the spring and block most of the signal (at which point,
I imagine the customer would be referred to the fine print on that
contract).
I think you can begin to see exactly where the bottom line is going
in this sort of arrangement. The private WISP approach is filled with
unanticipated (and expensive) challenges it comes to solving the
problem of ubiquitous access on a large scale. What hope does our
"wireless everywhere" vision have
in light of all of the previously mentioned problems? Perhaps a
massively parallel approach would help . . .
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