A look at a pair of Ethernet DSL bridges

ITworld.com –

If Digital Subscriber Line (DSL) service isn't available at your location, it probably will be soon. The telephone companies have finally started acting like high speed Internet access isn't something they want to hand off to the long distance carriers or the cable TV companies. As you probably know, DSL provides a digital signal on top of the same wires used to deliver conventional telephone service.

DSL operates in a frequency range that does not interfere -- too much, anyway -- with normal telephone usage. To block any stray noise, one or more filters are installed, either on each phone or at the place where the DSL can be split off. The current state- of-affairs is that you probably won't have much choice of which DSL bridge to install: the ISP you choose will dictate which one to use and if you use any other type they'll hit you with their favorite mantra: "We Won't Support You". However, this is bound to change -- remember when you couldn't buy a phone at all, much less get one from anyone other than the phone company? So, with an anticipatory spirit, I sought about acquiring what a couple of Ethernet DSL bridges to compare.

I wound up with two devices, one provided by my ISP, the other provided by the bridge vendor. My ISP, BELLSouth Internet Service, uses Alcatel and the bridge that comes with my account there is an Alcatel Speed Touch Home. Mindsprint/Earthlink uses ZyXEL and ZyXEL was kind enough to provide a Prestige 642M. Alcatel calls their device a "modem", ZyXEL uses the correct term and calls it a bridge. Both of these are intended to be single-user devices but can be used to interface a network with some external support. They are not routers, however.

To interface the devices to the computer, Efficient Networks EnterNet 300 software was installed. Because I have a dual CPU machine, I had to get my own copy of the software from Efficient Networks. BELLSouth has yet to upgrade to version 1.4 which supports SMP. Warning: while you can download the software from the Efficient Networks site on a 30-day demo and pay for a license, Efficient Networks offers no end-user support without a support contract.

As Ethernet devices, both of these boxes connect with a category 5 unshielded twisted pair (CAT5UTP) cable. The ZyXEL is configured to connect to a hub so it uses a straight-through cable to connect to a hub/switch or a cross-over to connect directly to a network interface card (NIC) on the computer. Alcatel is the other way: it uses a cross-over to connect to a hub/switch and a straight-through cable to connect to a NIC. The documentation that came with the ZyXEL was very clear on this matter. The physical documentation that came with the Alcatel was non-existent since it was installed by a BELLSouth technician (their requirement). However, the documentation downloaded from the Alcatel site was very clear and defined both uses.

Both devices come with a "default" IP address. The Alcatel is normally set to 10.0.0.138, the ZyXEL uses 196.168.1.1. Neither of these addresses conflict with anything on my network, so plugging the boxes into the network wasn't a problem. However, if these addresses are in use on your network, be careful when you install: you'll need to set up a private network to connect to the box and change its IP address before you plug it into the main network.

One of the big advantages (to me, anyway) of Windows 2000 over Windows NT is you don't have to reboot Win2K when you change or add an IP address. With that in mind, I added an address in the appropriate subnet for each device and tried to establish communications.

The ZyXEL Prestige 642M uses a Telnet interface to configure it. The bridge also has a serial port, which I didn't use. After adding a 192.168.1.x address to my NIC, I started a telnet program (TeraTerm Pro, a freeware program, is my favorite) and connected to the bridge. The password prompt appeared and I used the default password (provided in the documentation) to connect. The first thing I did was change the password. Then I changed the IP address to an address compatible with my network. The menu driven interface was easy to use. There are some entries that you really don't want to play with but, if you do, ZyXEL was kind enough to include a recessed "RESET" button on the back of the box that will reset the box to factory defaults. While I looked around in every menu option the only places I made any changes were in the password and IP address section. After that, I plugged the DSL into the ZyXEL, started the Enternet 300 software, defined a connection and I was on the BellSouth network using a device they refuse to support.

The Alcatel Speed Touch Home has both a Telnet interface and a Web browser interface. The browser is much easier to use than the Telnet interface because the Telnet interface is completely command-line driven: no menu at all. Stick with the browser. The first problem I encountered wasn't Alcatel's fault: BELLSouth changed the default IP address, so I couldn't connect to 10.0.0.138 even when I put a compatible IP address on my NIC. Fortunately, Alcatel also included a recovery path for this. While ZyXEL provides a RESET button, Alcatel provides several network based recovery schemes. I used the one the manual calls the "Ping of Life". The manual documents some easy steps to take under Windows NT or 2000 that involve use of the "arp" command. You put a special MAC address in the arp table with an IP address you chose, probably one that is compatible with your network but not in use. I picked an address that wasn't in use. I entered the IP address and the MAC address into the arp table in accordance with the manual. I started the Windows 2000 "ping" command against the IP address I used -- using the "-t" option on the ping command to keep it pinging until canceled. The Alcatel was turned off, then back on. In a few seconds, the bridge began responding to the ping. I was then able to use my browser to get to the configuration settings. The "ping of life" only sets the address in a temporary buffer -- I made the address permanent. There are other network actions that will perform a complete reset to factory defaults and they are no harder than the "ping of life".

The other big difference between these two devices is what services they provide. The ZyXEL is a pure bridge: it will take Ethernet packets and translate them to the appropriate ATM packets to go over the DSL. The Alcatel adds a few nice features: it can be a Dynamic Host Configuration Protocol (DHCP) server and a Domain Name Service (DNS) server. This indicates that Alcatel anticipates people using the Speed Touch Home as a network interface rather than a workstation interface. The browser interface includes some features that don't work in this model -- PPP (Point-to-Point Protocol), dial-in, "Classical IP" (CIP). These features would be more appropriate for real routers. Having DHCP and DNS available would be a big plus in a small (or remote) office where setting those things up might be difficult -- or costly.

Summary: You probably won't have a choice of devices if you want full support from your ISP, but both of these devices will get the job done. The Alcatel has some nice features that many users won't need or want, the ZyXEL does it's thing with minimal fuss and bother. If you want to connect a network through these devices, you'll need something to provide Network Address Translation service. Windows 200 Server and most UNIX variants have this built in. Or, an external box can be added to provide this service.

Insider: How the basic tech behind the Internet works
Join the discussion
Be the first to comment on this article. Our Commenting Policies