| For many home users and small businesses, 56K
modems no longer provide enough speed to perform many key functions. Users
are tired of waiting for downloads to complete and do not want to invest
in expensive dedicated connections, such as T1 lines. For that reason,
there has been much hoopla about both cable and Digital Subscriber Line (DSL)
modems recently. While TMC Labs has discussed cable modems at length (at
least in a few of Tom Keating's "Cc:" columns), we have yet to
discuss DSL modems, mainly because we are unable to attain a live DSL
connection at this time. When Celsian Technologies offered to let us use
some of their simulation equipment to test one of their DSL modems, we
jumped at the opportunity.
There are two main flavors of DSL -- asymmetric and symmetric. Both
provide high-speed data access across analog lines by using previously
untapped frequency bandwidth. The main difference between the two is that
ADSL provides a higher data rate when receiving (downloading) than when
transmitting (uploading), while SDSL has more of a balance, as its name
conveys. TMC Labs tested the Celsian Momentum U80 USB DSL modem, which
uses the ADSL flavor.
INSTALLATION
One of the biggest issues surrounding DSL modems is the difficulty with
the installation process. As with virtually all communications equipment,
users want the installation to be quick and painless. In many cases,
however, providing DSL connectivity has presented headaches for both home
users and small business administrators. Celsian Technologies claims that
they have made the extra effort to keep the installation of the Momentum
U80 modem as simple as possible.
We installed the DSL modem, hoping that Celsian's efforts had indeed
paid off. We had to install the software and drivers before we could plug
in the USB to our Windows 98 PC. This process did not present any
problems. After rebooting our computer and plugging in the USB connection,
Windows detected the new hardware, updated the Windows system, and
resolved any potential conflicts. However, it did ask us for the Windows
98 CD-ROM on a few occasions when searching for certain files. We just
clicked on the "Details" button to find out where the
destination file was and then entered that appropriate path to our C:
drive. This worked fine. Of course, using a Windows 98 CD would have
worked just as well.
Finally, we rebooted our PC one more time. Over all, this entire
process was certainly easy and took only minutes. The process may have
been even faster if we had used a Windows 2000 client because we probably
would not have needed to reboot our PC twice. The next version of the
software only needs one reboot during the installation process, even when
using Windows 98.
Normally, it would be necessary to ensure that the connection with our
ISP was properly configured, which has been an installation nightmare for
some DSL users in the past but has little to do with the Momentum U80
modem. For our testing, we were provided with a box that acted as the
central office. There were no problems connecting this system with the
Momentum U80 modem, and once we finished the rest of the installation
process, we opened the software and found that we were linked up
correctly. One anomaly we noticed was that while a shortcut was created
for accessing the software, we could not access the software from the
Start menu. It was listed, but when we clicked "Configure," the
DSL Modem Installer screen came up instead.
DOCUMENTATION
We were given two Word documents: 1.)the Support Manual and 2.) the
Installation Guide and User's Manual. The latter is a small booklet,
included with the Momentum U80 modem. The Installation Guide and User's
Manual explains all that one needs to know about the set up and operation
of the modem. For troubleshooting and support issues, the user would
likely call Celsian Technologies, where the Support Manual is distributed.
This manual discusses the "secret" element of the Momentum U80's
software -- certain mouse-clicks add more support and development
functionality. We will discuss more about this secret element in the
Operational Testing section. Over all, both manuals are sufficient for
their purposes.
There is a lack of help files for the actual software. Specifically,
after the installation is completed and the configuration software is
accessed, there aren't any help files. A help button is available, but
when we clicked that button, no help files were associated with it, at
least for the software version we tested (1.5). While help files are not
as important here as they would be with more complex software, they should
still be included. Celsian's Web site does not give much more information
either, but their Learning Center (a Web page that is under construction
as we write this review) may soon offer more useful information about DSL.
FEATURES
The following are the major features of the Celsian Momentum U80 USB DSL
modem:
- Provides a plug-and-play USB configuration in which an external
power supply is not required.
- Supports WAN (RFC 1577), LAN (RFC 1483), and ATM device drivers.
- Compatible with all T1.413, G.DMT, and G.lite-compliant CO DSLAM
equipment, as well as the vast majority of deployed CAP RADSL CO
equipment, and is multimode ready.
- Supports DSL upstream data rates of up to 1024 Kbps and downstream
data rates of up to 8 Mbps.
- Supplies up to 16 simultaneous ATM virtual connections.
- Includes a Microsoft Windows control panel monitoring program for
configuring the modem and checking the status of the connection.
- Claims interoperability with 18 DSLAMs.
- Software upgradeable.
OPERATIONAL TESTING
To test the Momentum U80 USB DSL Modem in our lab environment, we
connected the modem to an IPairGain box, which acted as the central
office. This box combined the DSLAM, ATM switch, and router into one.
Because of this setup, we could not test the speeds of the DSL connection
with any accuracy (the box not being a real ISP, CLEC, etc.), but we were
able to FTP and connect to the Web with the help of NT Server 4.0, which
we linked to the IPairGain box via an Ethernet LAN connection.
To simulate the distance in Kilo feet (Kft) of the DSL connection, we
used an XPS Wireline Simulator. In this way, we could tell how much the
data rate decreased as we simulated the connection to be further and
further away. From 1 Kft to 10 Kft, the transmitted and received rates
were fairly constant with ~640 Kbps for transmitted rates and ~6912 Kbps
for received rates, which also shows the asymmetry between upload and
download speeds. For some reason, the transmitted rates were slightly
lower from within a 1 Kft distance. Above 10 Kft, the data rate started to
drop considerably as the distance increased. For instance, at 12 Kft, the
transmitted rates were down to ~480 Kbps, and the received rates were down
to ~4736 Kbps. This decrease is to be expected at this far distance.
In the Documentation section, we mentioned the "secret"
element of the Momentum U80's configuration software. Accessing this
secret element helps support technicians and administrators with
configuration, monitoring, and testing issues that may not be of much
interest to most end users. These additional functions include a more
in-depth look at the configuration with ATM statistics available and
graphs detailing upstream and downstream bit loading and the signal to
noise ratio (SNR) margin per bin. Spectrum Reverb, Medley, Pilot, and R-MTPR
tests are the signal measurements for examining the DSL connections.
ROOM FOR IMPROVEMENT
There are many features that may be added to the Momentum U80's
arsenal. We would certainly suggest some type of remote configuration and
management, whether it is by using Telnet, SNMP, or a Web-based GUI. It
would also be nice to choose a DSL flavor (ADSL or SDSL) based on the
particular needs of the user. Better security, authentication, and quality
of service would also be of assurance for the user. Currently, the
Momentum U80 modem relies on the service provider for these important
features. The addition of support for VPN functionality with IPSec
encryption and support for NAT would go a long way in delivering secure IP
packets. Furthermore, a guarantee on the maximum amount of packet loss
could be placed for the assurance of the modem's performance.
Of course, it would be criminal if TMC Labs let our first DSL review go
by without a mention of adding voice over DSL (VoDSL) and PBX
functionality to the modem. After all, these are two of our favorite
topics. Voice over anything tickles our conversational tongues, and
subjects like voice mail, call waiting, and call conferencing keep us
happily on the phone for hours. Obviously, we think these features are
worthwhile.
Now that we've mentioned all of these features, keep in mind that most
of these improvements are already included in other Celsian products or
will be released with their upcoming new products. If they are added, the
price of the Momentum U80 USB DSL modem would probably have to increase.
Nevertheless, these features should still be considered for this
particular USB DSL modem, especially remote management, VPN, and VoDSL
functionality. As far as more mundane improvements, help files should be
added to the configuration software, as should right-click functionality.
CONCLUSION
For basic ADSL connectivity, the Celsian Momentum U80 USB DSL modem is a
solid piece of equipment. Its biggest strength is its ease of
installation. We were up and running in about the same time it takes to
remove the cover off a PC when attempting to install a traditional analog
modem. For those who would buy this equipment (mostly DSLAM vendors and
some ISPs, CLECs, etc.) and their prospective customers, this is a
blessing, especially for the often confusing installation process that is
dreaded when getting a DSL connection. If only other hardware were this
easy to install.
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