Step 2 is the hard part.

Matt Ginzton writes here.

DSL Modem Annoyances

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For my dual-line Fusion setup, Sonic.net sent me a Comtrend Nexuslink 5361.

It’s an ADSL2+ modem that works with one line, or two lines bonded together, and also includes normal home wireless router functionality (NAT firewall, 4 ethernet ports, and Wi-Fi).

My specific complaint here is that the way they wired it to accept 2 DSL lines is annoying. It’s got a single RJ14 jack, so both lines enter it there, on the inner and outer pair of the same jack. The problem is that it considers the outer pair to be line 1 (primary/master) and the inner pair to be line 2 (slave).¬†And if you connect only the slave line, it will establish ADSL sync but will not carry IP traffic (it looks like it never even acquires an IP address and gateway via DHCP).

If you connect only the master line, or both master and slave, then it works fine and carries IP traffic. But the way they wired it, it’s much easier to connect only the slave. (In fact, some Sonic.net support personnel told me they thought this modem doesn’t support single-line operation, which is probably because they’d tried plugging it in the straightforward way and found, indeed, it didn’t work.)

The reason this is a problem is that any single-line (RJ11) phone jack you have will only have the inner pair active. If you connect that to this modem with a standard phone cord (with either 1 or 2 pairs), you’ve connected the active pair to the inner pair on the modem, which is the slave line which will sync but will not alone carry traffic.

And the way AT&T’s wires terminate at the MPOE, each line goes to a separate test jack (an RJ11 jack, so on the inner pair), and a separate set of terminals, and it’s up to the customer how it’s wired from there. I connected an RJ14 jack to both lines, the inner pair connected to one phone line and the outer pair connected to the other phone line, which is the standard way of wiring a 2-line setup, and I can patch that jack directly to the modem with a standard 2-line phone cable to activate both lines. This setup is fine for actual use, but if I’m having problems, it’s unnecessarily difficult to troubleshoot.

The problem is that no standard phone cable gives you an easy way of connecting just the outer pair. A standard 1-line phone cable will connect the inner pair to the inner pair. A standard 2-line phone cable will connect both the inner and outer pairs to the matching pair on the other end. Sonic even gave me a fancy Y cable, which on one end has an RJ14 plug with both lines (inner and outer pair) active, and the other end has 2 separate RJ11 plugs each with only the inner pair. Using this Y cable, I can plug the modem directly into the MPOE, and connect both modem lines for bonded operation, or test single-line operation by connecting either single line to either the modem’s master or slave (in practice, since slave-only operation isn’t useful, it’s only useful to use the side of the Y cable that connects as the other end’s outer pair, thus goes to the modem’s master side). And also, I can hack the Y cable to work at my 2-line RJ14 jack to (in one direction) connect the inner pair on the line to either the inner or outer pair on the modem, or (in the other direction) connect the inner pair on the modem to either the inner or outer pair on the line (and if you’ve followed me so far, you’ll see that these 4 configurations are really just 3, and 2 of them connect only the slave line, so the only useful one is connecting the modem’s master line to the inner incoming pair, and there’s no way to test the modem’s master line on only the outer incoming pair, unless I build myself a cable that connects outer pair to outer pair while not connecting the inner pair).

The reason I’m complaining: this would all have been strictly better had Comtrend made the modem treat its inner pair as the master line. As it is now, you get the right result when connecting with a standard 2-pair phone cable to a 2-line jack, or using the fancy Y cable to connect to 2 separate 1-line jacks. But if you use a 1-line cable (to either a 1 or 2 line jack), or a 2-line cable to a 1-line jack, you’ll end up in the broken configuration, and this easily made mistake could have been easily avoided if they’d just configured the modem the more obvious way.

Why do I care so much about connecting this modem one line at a time, when it’s designed for bonded operation, you might ask? That’s a story for another time.

Update 4/16/2011: Sonic.net noticed this post, and called me to say that the various problems reported here have been fixed in updates by Comtrend to both the hardware and software. They were surprised I’d gotten one of the old modems, and are sending me a replacement (and even though most of the problems mentioned in this post only affect troubleshooting and won’t matter for real usage, I accepted the offer to see if the newer modem will help with any of the other problems I’m experiencing). +1 to Sonic.net for noticing this and being proactive.

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