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Controlling multilink calls on a server

Unanswered Question
Apr 19th, 2004
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A simple design requirement that I'm having trouble finding a useful solution to... Hopefully I'm merely overlooking something obvious...


Two dial-in servers using local authentication with about 100 lines each (ISDN PRI to 3640s).

Spokes using ISDN backup with all calls placed by spokes using a single BRI interface and no dial back.

Just enough lines for 1 b-channel per spoke if all spokes require ISDN backup at the same time (think disaster scenarios).

The Goal:

Under normal conditions, only a few to a few dozen spokes will need ISDN, so the desire is to use MLPPP for maximum possible bandwidth. The challenge is that as the number of spokes requiring ISDN exceeds 50% we need a way to force all spokes to limit themselves to a single B-channel without manual intervention or additional hardware.

Acceptable Alternative (if "the Goal" can't be met):

First "X" spokes to dial in get MLPPP, any additional spokes which call in get limited to a single channel (note that this requires provisioning extra PRIs to handle X 2-B-channel calls under worst case conditions).

Further Constraints:

Manual intervention is not acceptable--operation is 24x7 but staffing is only 8x5.

Local authentication is strongly preferred. Adding RADIUS or TACACS servers would have a major cost impact.

Dial-in servers also support other classes of callers and dial-out connections, so dialer profiles must be used, which eliminates BAP/BACP.

Single points of failure are not acceptable, nor are solutions which the TAC could not support (I don't want to be a single point of failure either :-).

Thanks in advance for any ideas which lead to a cost effective solution.

Vincent C Jones


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tepatel Tue, 04/20/2004 - 10:47
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Nope..what you are asking is not possible using IOS on cisco boxes. You can have AAA doing some intelligent piece of work where it can track of number of b_channel in use and then allow inbound connection accordingly.


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