THE UBIQUITOUS GR303 PROTOCOL
THE EVOLUTION OF THE DIGITAL LOOP CARRIER
Digital Loop Carriers began with TR-57, a Bellcore standard for extending the analog
loop with T1 spans. But TR-57 did not replace analog line cards in the switch - it only
added more of them, temporarily converting POTS back to digital in order to extend
tip & ring further out.
Enter the Integrated Digital Loop Carrier, where the spans to digitally carry POTS
originate in the switch itself. As originally conceived, IDLT spans would go directly from the
switch to the Remote Digital Terminal, saving money by removing the unneeded line
cards in the Central Office.
Then came the Broadband Loop Carrier that integrated DSL service with the POTS cards
at the RDT. Now a Central Office Terminal was needed to groom the voice services
from the DSL or FTTH data services. The IDLT is how voice is backhauled from the COT to the switch.
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