Big Upstream Upgrades


Delivering screaming fast
downloads may be the relatively
easy part.

For cable’s DOCSIS 3.0 deployments,
reaching comparable upload
speeds is another story. It
will take some heavy lifting to
boost upstream capacity, which
historically has been confined to
the noisy 5-to-42-Megahertz slice
of radio-frequency spectrum.

“The upstream is the Achilles’
heel for cable operators,” said Brian
O’Neill, senior marketing manager
for Motorola’s Access Networks
Solutions business unit.

And as the industry increasingly
aims DOCSIS high-speed-data
services at small and midsize
business customers, MSOs will
be under even more competitive
pressure to increase upstream
bandwidth. Many businesses rely
on big upstream pipes to transmit
large files and video, and
they’re accustomed to symmetrical-
bandwidth offerings such as
telco T-1 connections.

Moreover, “it’s not just best-effort,
as with residential,” noted
John Dahlquist, vice president of
marketing for Aurora Networks.

There’s no one-size-fits-all answer
to maximizing cable’s upstream
path. But regardless of the
approach, “you’re going to have
spend money to get there,” said
John Chapman, Cisco Systems fellow
and chief architect for its access
and transport technology group.

The good news: DOCSIS can
provide up to 1 Gigabit per second
upstream potentially for as
little as 10% of the cost of a fiber to-
the-premises buildout, according
to Chapman’s analysis.

Perhaps the most straightforward
technique is to perform
node splits, by allocating the 5-
42 MHz spectrum — capable of
delivering around 100 Mbps of
usable bandwidth with DOCSIS
3.0 channel-bonding — across a
smaller number homes (for example,
reducing a service group
from 500 homes to 100 homes).

Other approaches are more
complicated. Allocating 5-200
MHz for upstream data can provide
close to 1 Gbps throughput
without deeper fiber deployment,
but that would require eliminating
several dozen analog channels.
In Chapman’s “top split” scenario,
upstream channels could be
placed above 1 Gigahertz — but
that would necessitate more expensive
plant upgrades.

“The answer [for expanding upstream
DOCSIS capacity] will be
different potentially for business
versus residential,” Chapman
said. “It depends on whether you
have to support existing customers
on a segment.”

Motorola, for its part, believes operators
still have the opportunity to
boost the upstream by taking full
advantage of DOCSIS 2.0 features.

“The dirty little secret is that less
than 50% of the upstream channels
are using 2.0,” O’Neill said.
“There’s this whole latent potential
that just needs to be tapped.”