On 4/28/16 17:45, Sean Caron wrote:
[big snip] > I find the design of the CBX really interesting. IMO, their appearance > belies that ROLM was a computer vendor first a a phone equipment maker > second. Not in a perjorative sense, just stylistically. Comparing them > against boards from WECo/ATT/Lucent/Avaya, Nortel and Harris. I was a staff engineer at ROLM MSC between '82 - '86. By that time by any reasonable measure MSC and telecomm were two utterly different companies that happened to have common parentage; technology cross-over between the divisions was for all practical purposes nonexistent (although we did have the occasional employee move between divisions, particularly after the IBM debacle) -- but it certainly seems that experience building stuff on the MSC side informed *some* of the early design decisions on the telcom side. IIRC the most interesting thing about the CBX was that it could do so much with so little hardware (relative to other switches of the time) thanks to TDM of the 12-bit bus through the "connection table", which was a 384 slot recirculating command buffer that drove the codecs, dial tone generators, tone decoders, ring generators and the like. Basically the CPU would schedule the sender and receiver for the bus by dropping commands into two parallel queues (one for transmit, one for receive), so there was no need for bus request or arbitration logic and yet the CPU could be slow, as the sequencer would just advance through the buffer every 83usec processing the commands that it found. It was a pretty clever way of substituting DRAM for bus control logic while reducing processor requirements. MSC was effectively the alpha site for new builds and new hardware, and we saw failures that at times left us without reliable phones for a day or two. One of the more interesting was when the switch refused to honor extension status changes and instead entertained itself by ringing each extension *once* in ascending order, then repeating. -- Christian Kennedy, Ph.D. ch...@mainecoon.com AF6AP | DB00000692 | PG00029419 http://www.mainecoon.com PGP KeyID 108DAB97 PGP fingerprint: 4E99 10B6 7253 B048 6685 6CBC 55E1 20A3 108D AB97 "Mr. McKittrick, after careful consideration…"
