The line from your customer to the central office could NOT be digital, because if it were, it meant you are most likely connected to a SLC (aka remote terminal).
The goal of a SLC was to serve a remote area at low cost, by avoiding the need to deploy tons of copper. Most SLCs achieved this by taking a T1 (traditionally 24 POTS lines) and performing an analog-to-digital conversion AND compression (instead of giving you 64KB of bandwidth per channel, you got 16KB) to increase the number of voice lines that could be served.
So instead of deploying 96 pairs of copper, for 10 miles, at a cost of $$$$$ per mile, you deployed 2-4 pairs of copper for 10 miles at $ per mile plus the fixed cost of $$ for the purchase/lease of a SLC.
(The downside is the occasional line break caused by a car accident or hungry squirrel, would take down an entire neighborhood instead of just one customer)
On the provider side, you needed a provider that would deliver you PRIs with echo cancellation turned OFF on your channels.
Echo cancellation helped telecom providers, again, by saving bandwidth. With the advent of packet-switched networks, your voice calls were converted to digital audio, and sliced into chunks of 64KB, and delivered as packets to the remote switch.
Silence suppression was a common feature of packet-switched networks -- instead of delivering 64KB packets of silence, you delivered nothing, which allowed providers to reduce the aggregate amount of bandwidth they needed to service all the calls transiting their network.
With echo cancellation, it further increased the amount of packets the provider could drop to the floor which reduced their overall bandwidth needs. Your provider most likely marketed this new technology as "better quality voice calls" (remember the AT&T commercials inviting you to test the quality of their 'new digital network' for yourself, by calling 10-10-288-something and listening to a clip of Whitney Houston singing?)
The problem is, echo cancellation generates false positives on modem calls, and the subsequent silence suppression would cause 56K calls to retrain down to a level that would eventually not be effected by the echo cans, resulting in a 31.2Kbps or 33.6Kbps call.
This was a highly annoying discovery for providers who invested in brand new 56K-capable modem equipment.
Normally, you could just ask your provider to turn off the echo cans, but after the Telecom Act of 1996, a flood of new providers entered the market who were merely just reselling other larger carriers. This was a problem as your reseller probably didn't know what echo cans were, let alone had the "pull" to ask the underlying provider to turn it off on your behalf.
As an ISP, if you couldn't get echo cans turned off, then your only option was to cancel and find a new provider.
The line from your customer to the central office could NOT be digital, because if it were, it meant you are most likely connected to a SLC (aka remote terminal).
The goal of a SLC was to serve a remote area at low cost, by avoiding the need to deploy tons of copper. Most SLCs achieved this by taking a T1 (traditionally 24 POTS lines) and performing an analog-to-digital conversion AND compression (instead of giving you 64KB of bandwidth per channel, you got 16KB) to increase the number of voice lines that could be served.
So instead of deploying 96 pairs of copper, for 10 miles, at a cost of $$$$$ per mile, you deployed 2-4 pairs of copper for 10 miles at $ per mile plus the fixed cost of $$ for the purchase/lease of a SLC.
(The downside is the occasional line break caused by a car accident or hungry squirrel, would take down an entire neighborhood instead of just one customer)
On the provider side, you needed a provider that would deliver you PRIs with echo cancellation turned OFF on your channels.
Echo cancellation helped telecom providers, again, by saving bandwidth. With the advent of packet-switched networks, your voice calls were converted to digital audio, and sliced into chunks of 64KB, and delivered as packets to the remote switch.
Silence suppression was a common feature of packet-switched networks -- instead of delivering 64KB packets of silence, you delivered nothing, which allowed providers to reduce the aggregate amount of bandwidth they needed to service all the calls transiting their network.
With echo cancellation, it further increased the amount of packets the provider could drop to the floor which reduced their overall bandwidth needs. Your provider most likely marketed this new technology as "better quality voice calls" (remember the AT&T commercials inviting you to test the quality of their 'new digital network' for yourself, by calling 10-10-288-something and listening to a clip of Whitney Houston singing?)
The problem is, echo cancellation generates false positives on modem calls, and the subsequent silence suppression would cause 56K calls to retrain down to a level that would eventually not be effected by the echo cans, resulting in a 31.2Kbps or 33.6Kbps call.
This was a highly annoying discovery for providers who invested in brand new 56K-capable modem equipment.
Normally, you could just ask your provider to turn off the echo cans, but after the Telecom Act of 1996, a flood of new providers entered the market who were merely just reselling other larger carriers. This was a problem as your reseller probably didn't know what echo cans were, let alone had the "pull" to ask the underlying provider to turn it off on your behalf.
As an ISP, if you couldn't get echo cans turned off, then your only option was to cancel and find a new provider.