Monday, December 6, 2010

at&t Elite DSL and the D-Link DSL-520B

As promised, I had my DSL service activated a few days ago (on Friday).  Having returned to DSL and getting a chance to use it, I have made some interesting observations.  I also have some comments about the D-Link DSL-520B DSL modem I purchased.

The DSL service I purchased from at&t is the DSL Elite package - advertised as 6 Mbps down and 768 Kbps up.  According to my DSL modem's DSL statistics, my line is capable of supporting 9.504 Mbps down and 1.228 Mbps up, and is provisioned as 6.016 Mbps down and 768 Kbps up (as it should be).  In actuality, according to speed tests to several sites on I am getting about 4.8 Mbps down and 680 Kbps up.  The first number is rather disappointing.  It is showing at least 1.2 Mbps less than the advertised speed.  While this is within at&t's "fine print" speed range, it starts giving credence to Time Warner's (smear) advertising campaign that DSL is slow.  Compared to the measured rates I got on my cable modem (when it works), DSL is slow.  It would be advantageous to at&t to start giving customers a more realistic idea of what they should expect as far as bandwidth is concerned.  Giving 4.8 Mbps on a 6 Mbps line and calling it "within the range of service" is kind of like the auto industry's MPG ratings that bear no resemblance to reality.  When cable (when it works) is giving 7 Mbps (and I can really attain that speed) bursting to around 14 Mbps (I've measured this speed), 4.8 Mbps (best I can do) on DSL is pitiful.  No, I don't have Uverse available in my neighborhood.

That being said, while the performance of my DSL service is kind of lackluster, it appears to be reliable as I remember it.  The at&t technician called me before doing the installation and stopped by my house after he connected it to confirm that I had service.  Given that I did a "self installation," having someone check with me to make sure my service was working was a good thing.

The most irritating thing about the DSL installation was the account set-up.  If I must emphasize one thing to at&t, it is that they must not restrict service to ONLY Windows and MacOS users!  I'm not asking for you to give me OS support - I'm asking you to stop restricting me from registering my DSL service.  I was able to find some third-party solution to skipping the "unsupported OS" message but I should never have had to do this.  How much did Microsoft pay you guys at at&t to screw us Linux users?  Argh.

As I have said in the past, it is always a challenge to choose the lesser of two evils:  at&t or Time Warner.  Poor administrative support and slow speeds vs. we don't give a damn if your service works consistently or not.  Choose one or the other.

Instead of paying at&t for the Motorola (aka. speedstream) DSL modem for $65 or $69, I purchased my own DSL modem from Fry's Electronics for $50.  I purchased the D-Link DSL-520B DSL modem.  The device is fairly good and most definitely running Linux under-the-hood.  They pretty much use the Broadcom reference design (96338 board) for the BCM6338 system-on-a-chip (SOC) MIPS-based controller with ADSL2+ support.  The web pages are a bit cryptic in some places, and I am still not sure about some of the configuration parameters I chose, but the defaults (in most cases) seem to do the right thing.  After getting used to the modem, I was able to do some more advanced configuration.  The one thing I would like to do, and for whatever reason I can't, is to allow the PPPoE IP from at&t to be bridged to the Ethernet port and provided to me via DHCP.  Instead, you can only NAT, and the modem is the only device that is privy to your real IP address.  This means that if I run my own firewall and gateway, I need to double-NAT outgoing traffic, which seems stupid to me.  While the firewall in the DSL-520B is just Linux iptables, the web interface doesn't allow me to to do the fine-grained control I do on my own Linux box.  Also, while the DSL-520B has a dynamic DNS update client (for, I don't know how well it works or not and whether it renews my IP registration in 28 days as requires.  I would rather continue to run my own update client, which is kind of impossible to do reliably and efficiently when I don't have direct access to the real IP I am given.

All this being said, for the casual user, the device should work just fine.  In fact, if all you have are wired devices, you can connect the DSL-520B to a switch and let the built-in DHCP server, NAT, and firewall do all the work of a separate "router."  That could be useful for some users.

For those "l33t ha><0r" techie types, the DSL-520B gives you access to the underlying Linux OS and you can do a lot of very cool things.  If you telnet to the unit, you can get to a Linux shell prompt by:
$ telnet
Connected to
Escape character is '^]'.
Login: admin
> sh

BusyBox v1.00 (2010.08.18-23:32+0000) Built-in shell (msh)
Enter 'help' for a list of built-in commands.

Now, you are able to execute all the iptables commands directly as well as adjust adsl parameters, get all sorts of statistics, and otherwise control the entire box as you wish.  What I have not yet figured out is how to just bypass the dang web interface entirely and simply execute my own commands.  I bet given some time and thought, I could probably make some changes to overcome the bridging issue I mentioned previously.  Note that the OS and utilities all appear to be Broadcom's reference stuff, and that D-Link simply put their own web interface on it.  I'm not faulting D-Link here at all, it's just that (like many of these devices), the chipset can do really cool things but the OS implementation cripples some of the most innovative features.

I was debating whether to just return the DSL modem to Fry's and buy the Motorola modem (notorious for burning up in a few months to a year) or Actiontec or one of those...but given what I can see with the D-Link modem, I think I'll keep it and see if I can unleash some of its pent-up power (hopefully without bricking the unit).

I will try to keep everyone up-to-date on this subject should anything new and exciting surface while I experiment more.


Armil@dsl available in my area said...

Sometimes dsl service is disappointing but maybe there will be a progress about that in the near future.

By the way thanks for sharing your experience.

Anonymous said...

do some research and you'll understand that there is a 15-20% overhead for ADSL. that means that the 4.8Mbps you're seeing from a 6.0Mbps sync is exactly what it should be -- 1.2Mbps is 20% of 6.0Mbps.

cpu said...

Precisely my point.

I *did* do the research (eventually), and if there's 15-20% overhead in the way that DSL is implemented, then advertise the actual speed the user will see instead of a number that only a network administrator will understand.

When I went back to cable, the speeds that they advertised were the same speeds I was able to achieve. As a consumer, I don't care what the sync rate of the service is - I care about the rate I actually get. If the service is 4.8 Mbps for the consumer, then advertise it as such.

PS: If at&t really cared about the consumer, which I don't think they do, then they could have raised my sync rate to 7.2 Mbps (which would have achieved the 6 M advertised), since my line was able to handle a sync rate of up to 9.504 Mbps.

PPS: Yes, I also know that the fine print in at&t's agreement specifically says "sync rate," but again, that is useless for the consumer.

Anonymous said...

We used to complain about the fact that a hard drive's formatted capacity was lower than the number on the box, too.

We lost that battle. :P