STM-1 / USB interface?
This is a completeley crazy idea, but I couldn't resist doing some investigation and want to record my notes for future reference:
The XRT91L31 looks like an interesting chip; it does the STM-1 byte and frame alignment, as well as serial/parallel conversion. Essentially, it provides a 19.44MHz clocked 8-bit parallel input and output streaming the individual bytes. Each byte corresponds to one of the 64k sub-slots in the hierarchy. On the line-interface side it seems one can directly attach a SFP module to it.The Cypress FX2 looks like it can be used to construct a compatible interface. Its GPIF
- can be clocked from the external 19.44 MHz clock recovered by the receiver
- can interface the 8-bit parallel data and feed it from/to USB endpoints.
What would be the point? One could use (inexpensive, 2nd hand) E1/E3/STM-1 add/drop multiplexers to aggregate many physical E1 interfaces and bring them into a Linux system for software switching (e.g. via a PBX like LCR or FreeSwitch).