On a few rare occasions we are asked whether our products are Calix certified or Calix Compatible.  Calix charges each modem brand a high fee to become CalixCompatible.  Sadly, there are too many DSLAM manufacturers worldwide to bribe them all for their endorsement. Demands for such fees demonstrate a surprising lack of understanding about how ADSL modems are made and actually inhibit the advancement of ADSL technology. In a world where ADSL modem costs are falling rapidly, the unnecessary costs of such vendor specific certification programs limits customer choice and adds about 30% to the cost of a modem. The purpose of this paper is to explain how modems are made and try to educate certain DSLAM manufacturers about some fundamental concepts of interoperability.

We maintain that ADSL modems are essentially commodity items, at least as far as ADSL/ATM interop issues are concerned. All modems are made from the same basic reference designs from the chipset vendors. If you use the same chip, the same modem code and the same config, any two brands of modem will perform all interop tests exactly the same way. The modem code for these chips are made available to PCB (Printed Circuit Board) factories in binary form only, so there is no opportunity for brand differentiation on the basic modem code. If you specify a chipset and a version of the modem code, all modems that use that combination will behave the same way as far as ADSL/ATM interop is concerned. The reference design capability of the modem code is quite extensive, and includes all basic routing, management and ipTV functions.

The place that modem manufacturers can and do differentiate their products is in the application layer.  Some manufacturers add advanced features like dual-wan, printer ports, advanced VPN support, etc.  The typical low cost modem that telco's purchase have none of this differentiation.  Modems targeted for the telco market include only the basic reference design functionality and maybe a tweak here or there to the PHP code to modify the user interface a bit.

As DSLAM manufacturers charge each brand to become certified, they collect such fees knowing that the outcome is already a foregone conclusion. Given the chipset and firmware version, the testing lab already knows what will pass and what will fail and can simply fill out the paperwork and collect their high fee. For whatever reason, the DSLAM folks refuse to share the "correct" modem code, only disclosing that the current submission fails certain tests. The board manufacturer has no control of the modem code, so that news must travel around the planet from DSLAM labs to the board maker in China and back to the chip maker in the US. Armed only with pass/fail results and in the absence of any material reason for the failure, the chip maker re-sends another modem code version in the hopes the "new code" will work. This  "ping-pong" certification process continues until the chip maker, through a process of elimination, identifies the configuration that Calix, et al says works. It would be a lot better for everyone if Calix would just specify chipset / modem code / config.

This process discourages board makers from adding functionality to the application layer because any change must go through this whole certification process, even though the application firmware has no affect on DSLAM interop.  So what happens when you need a modem that has advanced functionality for a business customer?  Your answer must sound a little like: 'Sorry, we only sell black phones!'

Rather than looking for a "CalixCompatible" logo that unnecessarily increases their modem costs, customers should demand Calix publish their interop specifications so that modem manufacturers can build to that specification without going through the guessing game. DSLAM manufacturers should be expected to announce basic interop requirements to include chipset, firmware versions and configuration options. It would benefit the entire market if this were to become a standard question on all RFPs.

Here at Strowger, we support all DSLAM manufacturers.  Our modems have been tested with all and interop with all.  We offer free telephone technical support to telco customers and we believe our tech support is usually a lot quicker at identifying the root cause of problems than the paid support you get from the DSLAM maker.  If your customer needs advanced networking support, like help setting up a VPN, we do that for free too.  When is the last time Calix helped you set up a VPN, discover a port mapping problem or helped identify a mis-configured PC?