ESS also has to deal with a variety of inter-office singalling
> arrangements, which may include DC pulse transmissions and
> signalling from other offices of an older design. Now today
> everything is ESS but when these boxes came out there was still a
> great deal of step and panel out there.
I always found it somewhat amusing a No. 1 Crossbar office used revertive pulsing for signalling, even when commnicating with another
1XB office (each of them emulating a Panel Type office). Yes, there was a lot of Panel when 1XB came out.
I'll try to find my Bell Labs book to answer that.
In Bell Telephone literature, the No. 1 crossbar seems to be the forgotten step child. The articles always wax poetic about how the No. 5 crossbar was able to be modified to handle another new service or need; but the No. 1 is never mentioned.
The literature does describe the differences between the No. 1 and No.
5, but it's in technical terms--different functions were moved to different parts of the machine. But not described is how those differences affected actual operating functionality, maintainability, and reliability. I can't help but wonder if perhaps the No. 1 didn't perform that well. Indeed, only ten years after it entered service they brought out the much touted No. 5., though the No. 5 was intended more for larger suburban offices, not big city offices.
I also wonder which was retired last--No. 1 crossbar or Panel.
5XB was designed for small COs in suburbs, usually to replace SXS. 1XB was designed for large metropolitan COs, often replacing Panel, or those monster SXS designs.
5XB used the then-current manufacturing model, whereas 1XB manufacturing for growth probably ceased to exist (cf. many types of flat-spring vs. more-standardized wire-spring relays).
5XB used somewhat lighter (thinner) metal, therefore was likely cheaper to manufacture.
Wirewrap vs. soldering.
Cable racks for 1XB had cables neatly laced, but 5XB cable racks contained loosely-laid "piles" of cables on aluminum sheets. (This may be a local decision and not necessarily dependent on the switch). I could see WECo charging less to install a 5XB office or adding equipment. When they got to 1ESS, they had the cable racks at eye-level, filled them, then jacked up the whole system, sliding the bays in underneath, then dropping the racks.
5XB was faster for call completion, but it could block under heavy traffic, like several failures requiring the Trouble Recorder at the same time (snowball effect). 1XB could still push calls even in the heaviest traffic situation.
I can't remember now, but I think it was 5XB that gained some on speed by using some 130-volt relays, instead of 48-volt relays.
5XB used a balanced power load demand, where some relays were up while others were down when idle. 1XB was mostly everything down until used. This meant the power room for a 1XB office needed to be much tougher than a 5XB office, where the demand didn't fluctuate as widely. The daily power swing was fairly flat for suburban COs, while downtown COs had a lot of calls only during the working hours.
5XB used a pair of small ringing generators, while 1XB had large motor-generators, with mercury-filled interrupters, all mounted on a large table.
5XB had interrupters that used the W-Z "walking" relay theory, while 1XB used 1/20 HP AC/DC motor-driven Office Interrupter frames, just like Panel (same motors too). Think: lubrication, oil, cleaning, smell, ....
1XB used ANI from Number Networks to a CAMA office. 5XB used ANI from Translator Frames to LAMA Recorders (paper punches). At least in my area. I suppose this could be reversed easily.
Finally, all 1XB (and Panel) offices I've ever seen had a switchman on duty 24/7. The 5XB offices were usually unmanned at night, with their alarms sent remotely to a 1XB office. This may indicate that 5XB was designed with remote alarm sending and release in mind, while 1XB never had the capability to be remotely monitored, much less remotely retiring (releasing) alarms.
The 5XB had a Trouble Recorder that punched holes in large cards showing call progress up to the failure, and what equipment was used on the call. They could be examined the following morning. The 1XB office only had an OTI and a TTI for originating and terminating trouble. It was a panel with hundreds of 48-volt switchboard lamps, showing the call progress and equipment. It had to be manually released after manually recording the lighted lamps on a paper sheet.
The Subscriber Sender testboard also had to be manually operated to release stuck senders in 1XB. You could have a bunch of stuck senders (out of service) if there was another office failure, or a major cut cable somewhere.
So, maybe the cost of labor was creeping up and Ma Bell decided to run
5XB in a more automatic mode to cut down on tat cost?