The Open source SDSL Debug and Connectivity Unit (OSDCU) project was originally conceived in the summer of SE 45 (2006). It is named so because it was originally intended to serve as a debug and reverse engineering instrument first and as a practical SDSL connectivity device second. However, the situation has changed since then: we have now successfully completed the reverse engineering phase using our Hack-o-Rocket platform, and what we need now is a practical SDSL connectivity solution that is more elegant than the Hack-o-Rocket. That is the new purpose of the OSDCU project.
Here at Harhan we firmly believe in the principle of having a separate router and DSU connected by a modular synchronous serial interface. The OSDCU has always been meant to serve as the DSU for SDSL/2B1Q, not a router, but the question which remains to be settled is the form factor.
The original plan was to put an EIA-530 DCE port on the OSDCU board, making it a single-board DSU. It would be perfect for those who want a DSU to connect to a larger external router/gateway, but would make it difficult to piggy-back the DSU with a little router in the same enclosure. We have considered an alternative option of making our OSDCU piggy-back with an MPC8xx board from Embedded Planet (the latter board running Linux or BSD would have acted as an open source router module), but this idea has been abandoned because we could not find a board in EP's repertoire of products which would both fit us well technically and be available on economically viable terms for our non-profit project.
We are now going back to our original plan of making the OSDCU a single standalone board (our own 130x165 mm form factor) with an EIA-530 DCE port. For DSU operation it won't need anything else besides a power supply, and here at Harhan we plan on connecting it to our 4.3BSD-Quasijarus router with a DSV11 synchronous serial interface card. The EIA-530 interface should also connect easily to Cisco routers with DB60 WAN ports.
What about those who want a single box which goes from SDSL all the way to Ethernet like the Hack-o-Rocket? Well, although it won't be as pretty as mating with an MPC8xx router board directly, one could make a router board that would match the OSDCU in outline and which would be mounted either above or below the OSDCU board in a suitably designed enclosure. The two boards would connect with an internal ribbon cable; on the OSDCU end that cable would plug into the EIA-530 DCE port. (We'll give some more concrete suggestions after we build the OSDCU itself.)
The OSDCU will be a totally bit-transparent DSU for SDSL Flavor B: the RS8973 bitpump's RDAT and TDAT pins will be MUXed directly to the EIA-530 DCE port. However, it will also enable connectivity to SDSL/ATM (both Flavor A and Nokia) by acting as a Layer 2 protocol converter from ATM to HDLC. There are a number of industry standard ways for doing this conversion; our only real concern here is whether our CPU can perform this conversion fast enough to keep up with high data rates (Covad SDSL for example can go up to 1536 kbps). We'll have to just try it and see how well it works.
The design was almost complete and ready to go into layout in the fall of SE 46 (2007) when the project's principal engineer suddenly had a context switch. We are almost ready to resume the project; please stay tuned.