article continues a series that I started in 1998 and 1999 about broadband
high speed communications connections. A two part article done for this
column in August and September 1998 contained an overview of bandwidth
as it relates to high speed telecommunications connections. The August
article, Part 1, defined bandwidth, discussed technologies that existed
then, and covered costs being offered at the time. Analog or POTS
the commercial direct T-1 digital services were covered. The September
1998 article, Part 2, looked at the, in 1998, proposed broadband capabilities
offered by Direct Cable and ADSL (Asymmetric
to be offered by the cable TV and telephone companies in San Antonio. Then
in separate columns in 1998 and 1999, I covered the Paragon (Time Warner)
direct cable technology approach, and, the Southwest
Bell ADSL technology approach. Finally, in June 1999, I covered a broadband
bandwidth comparison between the two San Antonio providers, Time Warner
and Southwest Bell.
This column will begin a real-world DSL/Direct Cable comparison from
my experience using both services. I currently have both a direct cable
(Roadrunner) and a DSL connection up and running. This report will be a
summary of my subjective feel for each of the services.
Some review of the overall technologies should be covered here before
forging ahead. Remember that our bandwidth definition concerns both the
amount of data as well as the speed at which the data is moved. The true
definition of bandwidth therefore concerns both size and speed and is measured
as bps (Bits-Per-Second).
The current analog POTS dial-up modem technology delivers data at a rate
of approximately 52,000 bps, depending on the condition of the POTS telephone
line being used. ISDN service, also a dial-up service, is the first digital
capability available over the POTS telephone line twisted pairs. ISDN service
operates at 128,000 bps, both up and downstream. T-1 service is a dedicated
direct connection that delivers 1,540,000 bps. T-1 service has been used
as a dedicated commercial service that large business accessed between
its own connections. T-1 was known as a leased line service. There are
connections in the T-1 range at multiples of that speed such as T-3 which
contains multiple T-1 lines. There are higher speed connections even than
these in the SONET (Synchronous
connections that operate at multiples of 51,840,000 bps (STS-1 etc.). Remember
that all of these connections above the ISDN level are digital and direct
meaning that they move the data in parallel and are open or hot all the
The ADSL connection, for example operates at the lower end of the SONET
capabilities. It functions over existing twisted pair phone cable and operates
in a frequency range outside that of the audio phone frequency, i.e., the
phone audio and the data can function at the same time. Its data flow is
all digital. ADSL speeds are in the 1 to 8 Mbps range downstream and in
the 100 to 800 Kbps range upstream. It can be a dedicated connection, i.e.,
one with a dedicated IP address or it can be dynamically assigned. Dedicated
connections operate at the higher speeds and cost more to use. A broadband
modem is used to receive and send data over the connection in either mode.
The ADSL connection is provided over an existing POTS telephone line. The
broadband modem receives itís signal from the POTS twisted pair and then
feeds it to the computer NIC (Network
or router via an Ethernet cable. The receiving computer or router either
accepts the signal dynamically or as a static IP address. In either case
the ISP connection is direct or open to the outside Internet world.
There is a law of physics involved with providing ADSL connections.
The distance that can be supported by the signal on the POTS telephone
line is 18,000 feet. In the real world this distance is shorter. SW Bell
uses something under 17,500 feet. This means that the telephone infrastructure
must be modified to accommodate data users in any given telephone subscriber
area. The digital portion of the telephone infrastructure must be moved
out from the CO (Central
handling the service. SW Bell has spent an enormous amount of capital in
adding these extensions to their system infrastructure.
The Direct Cable connection uses the CATV (Cable
TV) video spectrum
to provide its broadband capability. The video spectrum ranges from 6 MHZ
to 750 MHZ. The TV video uses from 55 MHZ to 550 MHZ and is the majority
user for this medium. Cable has one way access downstream within the 550
MHZ to 750 MHZ frequency spectrum. Within this upper frequency spectrum,
there is a clean RF (Radio
of providing 20 to 30 Mbps downstream. Up stream access in the 6 MHZ to
55 MHZ frequency spectrum. This spectrum provides a clean RF channel capable
of 2.5 Mbps upstream. The cable company usually limits the downstream connection
to 10 Mbps and the upstream to 2 Mbps.
Again, a broadband cable modem converts the RF signals into digital
information and vice versa. The signal comes into the modem via a RC59
BNC coaxial cable. The modem connects to the computer NIC or router via
an Ethernet cable.
This connection is on a shared access network, i.e., each cable data
node (connection) is part of a computer subnetwork in the cable grid. This
is the reason for the 10 Mbps downstream and the 2 Mbps upstream limitation.
This insures that everyone on the subnetwork will have access. As noted
in the previous article, there are two issues that need to be covered about
shared access networks. First, everyone on the subnetwork gets a piece
of the available bandwidth just like any network. The more subscribers
on the network, the less bandwidth each subscriber will have available
at any given time when everyone is simultaneously using the network. Second,
direct access on a shared network means the same thing it means on any
shared resources at the host computer can be seen by others on the same
subnetwork. This is a security issue. The cable company insures that everyone
on the subnetwork has access by limiting each subnetwork. In the case of
Time Warner Road Runner (RR), each subnetwork contains no more than 450
subscribers. As with ADSL, the direct cable connections can be provided
both dynamically and as static IP addresses. The connection is direct or
open all the time as with ADSL.
A Real World Subjective Comparison
As noted above, I have both a ADSL and Direct Cable Internet connection
for test and work comparison use. Both are dynamically provided by the
respective ISP, Sbcglobal.net and Roadrunner. The RR connection has been
in use longer than the ADSL connection because SW Bell took longer to build
the required infrastructure to service my home area, i.e., the final 17,500
feet. As a cable TV subscriber, I already had the direct cable connection
to my house.
The RR connection was simple to setup. Once I had subscribed to RR,
an account was established providing me with dynamic access to the RR ISP.
The RR technician installed the data splitter onto my cable TV line and
ran a BNC cable to my office. I installed the provided direct cable modem
and the connection signal was there. Everything worked well with RR.
Until, after about one and one half years of service, I started getting
down time when it rained. The service signal would start and stop suddenly.
It took about 60 days and several service calls to find out the problem
or problems. There were two. One concerned the sudden down time. It seems
that the TV cable from the line on the utility pole in my back yard was
run under a limb of an oak tree there. The TV cable had become taught due
to limb growth and when the wind moved it, the cable would slip out of
the utility pole connection cutting the connection. By the way, my TV service
also stopped when this happened, as I discovered well into the 60 day problem
period. A new line to house cable was installed with plenty of slack in
it. Then, the second part of the problem started to manifest itself. After
a rain, my RR service would stop or slow down. Mainly it stopped and any
number of modem reboots, (unplug the modem power for about 30 seconds)
would not get it started. Then, about an hour or two later, the system
would be back in operation with no outside help. During these events, the
first five TV channels and the last four channels would be grainy or out
of focus. After more technical service calls, the main line to house connection
was swapped out. When opened, it was corroded. Together, these two fixes
have gotten the direct cable service back on continuous operation.
There are periods when the subnetwork is actually slower. It is because
the bandwidth is being used by most of the subscribers in the subnetwork
for this area. An occupational hazard.
The ADSL service, once SW Bell got its infrastructure in place has been
operating without any problems at all. It seemed to be a bit harder or
more complex to install than the RR service. There were far too many steps
to jump through to get it up and running.
Both function as computer to modem connections and through broadband
routers without problems. I use both connections on my SOHO network. Both
access the Internet equally well via individual computers and the network.
Performance, i.e., throughput is also consistent. The direct cable connection,
either from a single computer or from the network, is faster both upstream
and downstream. The www.satx.rr.com
site has a speed test link on it. There are two local tests that can be
conducted from this site. One sends and receives data. The other is a up/download
of a 1.8 GB graphic. I did an informal test on each connection over the
past few days and have come up with these numbers.
The Direct Cable RR connection has consistently provided faster throughput
as different times of the day. An average of nine data speed tests done
at different times of the day was 2723.4 kbps downstream and 332.9 Kbps
upstream. The speed test graphic average was 1903.3 downstream and 238.0
The ADSL connection done at the same time provided an average of 1143.3
Kbps downstream and 140.2 Kbps upstream on the data test from the same
site. The graphic test averaged 1145.7 downstream and 142.7 upstream.
The costs of the two services are nearly equal. The RR connection costs
$44.95 per month. The DSL connection costs $49.95 per month.
My conclusion is that either broadband connection will work for the
home user/SOHO setup. Faster is better and both provide more than enough
capability. I will touch on my security arrangements in up coming articles
concerning these connections.