WHY GR303?
THE TR-08 PROBLEM
The first IDLC protocol was TR-08, and it was really just an adaptation of the old channel bank.
TR-08 comes in several flavors, but they have a few things in common:
- Fixed assignment of lines to spans.
- Limited concentration.
- Protection bandwidth is dead bandwidth.
Because of the fixed assignments, it's important to
have a protection span in each group. But for the same reason, the protection span sits idle until
something fails. And the choices for concentration are few: 1:1 and 2:1.
The result is that TR-08 needs lots of spans. In a Stromberg line frame, for example, it takes a minimum
of 33 spans to serve 960 lines.
WHY GR303 IS UNIVERSALLY SUPPORTED
GR303 differs from TR-08 in key ways:
- Dynamic assignment of lines to spans.
- Variable concentration.
- Protection is accomplished by load-sharing.
Dynamic assignment means a line is assigned any open channel on any span, when a call is set up.
Variable concentration means that any number of spans may be provisioned, up to 28, to support
any number of lines, up to 2048. Since all spans load-share, there is no idle protection span.
The result is a single GR303 interface of 8-10 spans can support the same 960 lines in the
example given above.
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