23 ms·
> Until some makes a call or sends a fax when your top speed drops 64k per phone line being used. That wasn’t how it worked. You could have a T1 with certain
by marcus0x62 3y ago
> Until some makes a call or sends a fax when your top speed drops 64k per phone line being used.
That wasn’t how it worked. You could have a T1 with certain channels configured for voice and others for data, but the configuration was static — you didn’t get to use the bandwidth from the voice channels when they were idle.
> It’s also why ISDN didn’t connect at 128k but at 112k since it just used two “bonded” lines of the T1
ISDN bearer channels were 8-bit clean. If you bonded both channels of a BRI, you had a 128kbps data path. What you typically couldn’t use was the 16kbps D channel, which was used for signaling.
- InvaderFizz 3y agoCorrect. And IIRC, IDSL was just ISDN with all three channels dedicated to data. Yielding 144kbps at phenomenal distances from the CO.
- Aloha 3y agoIDSL was an ISDN bearer with Frame Relay running on top, it basically didn't use the channelization scheme at all - and IIRC had different framing than a real BRI line.
- marcus0x62 3y agoIDSL used HDLC natively as a frame format. You could run Frame Relay on top of that (or PPP.) Line coding was standard 2B1Q in North America (same as a “regular” ISDN BRI.)
- tbyehl 3y agoSome ISDN TAs supported data-over-voice for 56kbps per channel. Useful in areas where data calls has per-minute charges but unlimited local "voice" calls were included in the monthly charges.
- marcus0x62 3y agoRight, and some TAs supported data notifications over the D channel. There was also 144kbps IDSL which made use of the D channel bandwidth. And a bunch of other variations. But, the fundamental channel width was 64kbps and ISDN data calls were not routinely connecting at 56kbps due to robbed-bit signaling, which the GP comment claimed.