VersaDSU is a manufacture-on-demand product made from our OSDCU design which we have released free to the world. We take great pride in not holding any kind of intellectual property: you are more than welcome to download the design files for our product and try to build it yourself, or you can buy a known-working, ready to use unit from us that is packaged in a high-quality enclosure and comes with warranty and support.

VersaDSU is a CSU/DSU for SDSL. It does for SDSL what the traditional CSU/DSU products have done for T1 and DDS data transmission technologies: convert the SDSL electrical signal format to a standard synchronous serial interface which can be connected to any classic WAN router that accommodates traditional T1/DDS DSUs. Thanks to the VersaDSU, enterprise SDSL users are no longer forced to use consumer-oriented soapbox routers which go from SDSL to Ethernet with no flexibility, instead the serious enterprise user can now convert SDSL to EIA-530 (similar to V.35, see below) with the aid of a VersaDSU and connect it to a traditional enterprise-grade router such as Cisco 1600 or 2500 series.

SDSL flavor support

A major distinguishing feature of SDSL is the multitude of different flavors. Harhan has been leading an open source project since 2005 called the Open SDSL Connectivity Project which undertook to identify and reverse-engineer some of the most widespread proprietary SDSL flavors, and the VersaDSU product builds upon the successes of that project.

The two most dominant flavors of SDSL in North America are Copper Mountain and Nokia, used by Covad. Our DSU product supports both flavors. (With Copper Mountain SDSL the bit stream on the line is already in the right format to be fed to a standard WAN router, hence VersaDSU configured for CM is totally bit-transparent. The Nokia/Covad flavor puts ATM cells with proprietary framing on the line, which is not useful to a standard WAN router, hence VersaDSU configured for this flavor acts as a Layer 2 converter from ATM to HDLC. See the OSDCU page for the latest performance figures.)

Campus modem / private line operation

In addition to acting as a CPE device interoperating with various SDSL flavors established by DSLAM vendors (STU-R mode), VersaDSU can act as service provider equipment (STU-C mode) serving out the IFCTF flavor of SDSL/2B1Q. The product thus enables private line or campus modem operation over a dry copper pair using two identical VersaDSU units on both ends, one configured as STU-C and the other as STU-R. The maximum data rate will depend on the loop length and quality as usual with SDSL, the maximum being 2320 kbps over short loops of high quality.

Other specifications

Form factor

The enclosure dimensions are 8.298 in wide, 6.611 in deep and 1.786 in high. The enclosure is made of sheet metal and rests on rubber feet.

Power

VersaDSU takes AC power (American or European auto-switching) via a standard IEC 320 mains entry connector like the one found on common computer power supplies. It has an internal switching power supply.

Synchronous serial interface

The synchronous serial hand-off interface uses a female DB25 connector with EIA-530 pinout. The electrical interface is EIA-422 for the data and clock signals and EIA-423 for the modem control signals. Although this interface is slightly different from the V.35-style one used by most T1 and DDS DSUs, all major WAN router synchronous serial ports to our knowledge support both interfaces, and we have found the DB25 connector to be much more convenient than the extremely bulky V.35 one.

If you are connecting to a Cisco WAN router with 5 in 1 or smart serial ports, Cisco makes a cable that goes from their connector to an EIA-530 DCE, and that cable should be optimal for use with the VersaDSU.

It should also be noted that CCITT Recommendation V.35 has been withdrawn by its authoring standards body and that the recommended replacement (a combination of V.10 and V.11) calls for exactly the same electrical interface as we have implemented on the VersaDSU.

Maximum data rate

2320 kbps or the highest rate supported by the service provider, whichever is less.

Microprocessor and software

VersaDSU uses a Freescale MC68302 microprocessor; all software running on this microprocessor (implementation of different SDSL flavors, board management, control dispatch, configuration wizards) is totally free / open source.

Configuration mechanism

A craft terminal port (asynchronous serial, 9600 baud) is provided on an RJ45-style connector using the same pinout as the console ports on Cisco routers. This port provides full access to all functional software on the VersaDSU board, including a configuration wizard utility which allows the DSU function to be configured for different SDSL flavors. Once the configuration is entered, it will be saved in an on-board flash file system.

We can also ship VersaDSU units preconfigured for a particular SDSL flavor at the factory.

Status monitoring

There are 4 LEDs on the front panel indicating power, unit operational status, line status (condition of the SDSL link) and the DTR signal from the WAN router. More detailed status information is available through the craft terminal port.

Availability and pricing

The list price for the VersaDSU is $500 (USD); it has been set approximately equal to the list price of a similar product that used to be made by Larscom around 1999/2000. Special discounts are available for hobbyists and non-profit organisations.

Because the product serves a highly specialized application, we do not maintain stock; instead the product is manufactured on demand upon placement of a non-cancelable order. All orders are subject to lead times.

Please email sales@harhan.com to place an order or request more information.