The company I worked for in the 2000s had both kinds of T1: They had a single CAS (channel-associated, or "robbed bit", signaling) T1 from one carrier, an two PRI (ISDN) T1s from another carrier. The two PRI T1s only had one channel for signaling, and 47 channels for voice calls.
Our block of phone numbers (we had a block of 500 or 1,000 numbers) was tied to the PRI T1s; for the CAS T1, we were allowed to use our number block as the "calling party" number for outgoing calls. If the PRI T1s went down folks wouldn't be able to call us, but we could call them and the called parties wouldn't notice any difference.
As opposed to E1 links in Europe. Same same until you want to patch a US T1 to a European E1. Some sweet hardware money was made dealing with that. ( different framing, 2mbit/s instead of 1.44, 56kbps splits vs 64kbps splits. Clocks are a nightmare.
Story is that Bell tested the T1 in comms pits around Murray Hill NJ and when it worked for a long city block between two manholes they knew they had a product they could sell.
Watched a telco guy fix a broke E1 by sending one of the pairs a bit further round the krone frame to separate the signals better. I've even seen them add more wire to try and dampen down some local noise or reflectance or harmonics or something.
The old E1/T1 lines were sometimes pressurised and came with fancy brass taps to let the water out with its own teeny weeny bucket hanging off the tap. I kid you not.
> Early versions of DS1 only actually carried 7 bits for each sample, which was sufficient for a telephone call when companding was used to recover some of the dynamic range. The eighth bit was used for framing.
A book I have says the eighth bit was initially used to indicate on-hook/off-hook status, not framing.
This is correct. There's more. An incoming call was indicated by a solid "seizure" or activation of this bit. The receiving end would "wink" back to indicate that it would accept the call. This was ~0.5 sec blip "on" in the reverse channel. The sending channel could then transmit whatever information was arranged, e.g. internal extension number, called number, calling party number. After any data was transmitted via audio as DTMF or MF, if the receiving end decided to answer it would "seize" in return. In theory, the call ended when either end "dropped" the bit, however it was often the case that when calling into lesser modern destinations for example, the call only ended when the calling party ended it, leading to some fun empirical solutions :)
The company I worked for in the 2000s had both kinds of T1: They had a single CAS (channel-associated, or "robbed bit", signaling) T1 from one carrier, an two PRI (ISDN) T1s from another carrier. The two PRI T1s only had one channel for signaling, and 47 channels for voice calls.
Our block of phone numbers (we had a block of 500 or 1,000 numbers) was tied to the PRI T1s; for the CAS T1, we were allowed to use our number block as the "calling party" number for outgoing calls. If the PRI T1s went down folks wouldn't be able to call us, but we could call them and the called parties wouldn't notice any difference.
As opposed to E1 links in Europe. Same same until you want to patch a US T1 to a European E1. Some sweet hardware money was made dealing with that. ( different framing, 2mbit/s instead of 1.44, 56kbps splits vs 64kbps splits. Clocks are a nightmare.
Story is that Bell tested the T1 in comms pits around Murray Hill NJ and when it worked for a long city block between two manholes they knew they had a product they could sell.
Watched a telco guy fix a broke E1 by sending one of the pairs a bit further round the krone frame to separate the signals better. I've even seen them add more wire to try and dampen down some local noise or reflectance or harmonics or something.
The old E1/T1 lines were sometimes pressurised and came with fancy brass taps to let the water out with its own teeny weeny bucket hanging off the tap. I kid you not.
> Some sweet hardware money was made dealing with that
I used to work in a company that made good money on those
> 24, 4, 7, it has the upsetting feeling of a gallon being four quarts each of which is two pints.
A gallon is two pottles; a pottle is two quarts; a quart is two pints; a pint is two cups; a cup is two gills. And a gill is two jacks!
24 and 4 don’t strike me as unusual numbers (two dozen and two doubled), but seven does.
> a different media
‘A … medium.’ One medium, two or more media.
> Early versions of DS1 only actually carried 7 bits for each sample, which was sufficient for a telephone call when companding was used to recover some of the dynamic range. The eighth bit was used for framing.
A book I have says the eighth bit was initially used to indicate on-hook/off-hook status, not framing.
This is correct. There's more. An incoming call was indicated by a solid "seizure" or activation of this bit. The receiving end would "wink" back to indicate that it would accept the call. This was ~0.5 sec blip "on" in the reverse channel. The sending channel could then transmit whatever information was arranged, e.g. internal extension number, called number, calling party number. After any data was transmitted via audio as DTMF or MF, if the receiving end decided to answer it would "seize" in return. In theory, the call ended when either end "dropped" the bit, however it was often the case that when calling into lesser modern destinations for example, the call only ended when the calling party ended it, leading to some fun empirical solutions :)