[VoIP] Another WE question

[Steph Kerman]

John R. Covert wrote:
>> Autovon was a 4W network
> Although Autovon was a 4W network, 99.99% of Autovon calls were placed 
> by "users", not "subscribers". Users did not have special phones at 
> all. Autovon "users" accessed the network by dialing "8" from the PBX 
> or Centrex serving the military installation. So even though every 202 
> OXford x-xxxx number at the Pentagon also had the Autovon number 
> 22x-xxxx, not one of those phones was a four-wire phone.
>
> Only Autovon "subscribers" on direct Autovon lines running directly 
> out of the hardened Autovon switches would have been arranged for
> 4-wire operation. Thus the four-wire phones were rare, and would 
> almost always be an additional, separate phone except in those rare
> places where no PSTN access was needed (since there was no direct PSTN 
> access from Autovon, one always had to ask a base operator somewhere 
> to extend the call as a courtesy).
The purpose of support for mixed 2W/4W operation on 3568 sets was 
ostensibly to allow 2W PBX EXTs or PSTN lines as well as 4W Autovon 
lines on the same set.  I don't know to what extent the feature was used.
> I think the 3568 phones could be arranged so that the 4-wire 
> capability was only in effect on certain keys, so that it was possible 
> to have both 2-wire PBX and direct Autovon lines on the same set in 
> the same key system, 
Definitely was included in the design.
> but I never saw this done, which is not to say that somewhere with 
> direct lines on a large number of desks this was not done.
>
> Every phone with a type 66 Autovon keypad which I ever saw was a 3568, 
> even if there was only a single line on the phone. There were a few 
> special arrangements in tactical consoles where there would be a type 
> 66 keypad in the console connected to some sort of custom arrangement.
There must have been 3504 sets in use somewhere since they show up on 
eBay.  The three 608 cord positions at one Navy base I know of had 
66-type dials added on the keyshelves.  The cord boards were connected 
to a large 701B Centrex with "PBX Access Lines"...  4W trunks into the 
nearest Autovon switch that were accessed on a 2W basis from 701B EXTs.

The PBX also had Preempt Tone supplies in the tone plant.  I saw this at 
two 701Bs which had PBX Access Lines.  I believe they were associated 
with the Access Lines.  Since there were no DTMF receivers in either 
installation that would have been capable of recognizing 4th column 
tones, I'm inclined to think that the Preempt feature was invoked 
towards the PBX from the Autovon switch.
> <snip>
>
> A four-wire arranged phone still did all of its loop signalling on a 
> standard loop circuit which carried the transmit (from the phone) 
> path; this was connected to the network in the normal manner. The 
> four-wire difference was that the receive path went directly (through 
> only surge protection) to the receiver. I'm pretty sure the 3568 sets 
> also had a small local side-tone generation circuit to provide a 
> natural feel.
The sidetone path was part of the line interface circuit in the Key 
Service Unit, not part of the phone.  It also included a line amplifier 
with low Z output to allow multiple telephones to be driven without 
reduction of receive level.  However 3568 sets contain a crystal can 
relay to transfer the receiver between the internal speech network and 
receive pair depending on whether a 2W or 4W PU key is pressed.

Steph