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0 pointsaidenn09y ago0 comments

Are you sure you're not thinking of T-1 (24 B channels) rather than ISDN which was most typically 1 or 2 B channels?

[edit]

ISDN is a catch-all term tat included BRI (2 B channels) and T-1 (24 B channels) and E-1 (30 B channels) so the parent comment is correct.

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jsjohnst9y ago

Your edit mostly got it right with the exception that it wasn't commonly called a T-1 or E-1 and the numbers are slightly off.

* ISDN BRI = two 64k B channels and one 16k D channel

* ISDN PRI over T1 = twenty three 64K B channels and one 64k D channel

* ISDN PRI over E1 = thirty 64k B channels and one 64k D channel (time slot 0 on the E1 was used as a sync channel and wasn't considered a B or D)

T1/E1 was considered an analog circuit with 24 or 32 respective 64kbps voice channels using in band signaling effectively limiting each channel to 56k. ISDN PRI used the same cabling and channel separation, but instead ran a digital circuit with out of band signaling enabling the full 64k to be available for voice and data. ISDN PRI (and BRI) also allowed the option to be packet based (similar to X.25) rather than circuit switched for data transmission.

aidenn0OP9y ago

In the 90s in my little corner of the mid Atlantic US at least, it was very commonly called a T1 or DS1 and the terms were used interchangeably even though they refer to slightly different things (at least by sysadmins; use the terms wrong around a telecom equipment engineer and you'd likely get corrected).

jsjohnst9y ago

I'm aware the misnaming was common, but it's a bad idea to do so. There's a pretty big difference between a T1 and a PRI in practice when used as a data only circuit. For one, the T-1 is a fair bit faster.

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jsjohnst9y ago

Your edit mostly got it right with the exception that it wasn't commonly called a T-1 or E-1 and the numbers are slightly off.

* ISDN BRI = two 64k B channels and one 16k D channel

* ISDN PRI over T1 = twenty three 64K B channels and one 64k D channel

* ISDN PRI over E1 = thirty 64k B channels and one 64k D channel (time slot 0 on the E1 was used as a sync channel and wasn't considered a B or D)

aidenn0OP9y ago

jsjohnst9y ago

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