
Dial Services Overview
1-9
Configure the primary and backup lines as follows:
• Primary — Any leased line up to T1/E1 rates, and Frame Relay PVCs (using
virtual circuits in direct mode). Protocols supported: Standard, PPP, Frame
Relay (direct mode only).
• Backup — Any available synchronous or ISDN line.
Protocol supported: Point-to-Point (PPP).
Figure 1-5 and Figure 1-6 show how dial backup lines support primary circuits.
Figure 1-5. Dial Backup Support in a PSTN
Router
Router
Router
Remote Site C
Modem
Remote Site B
Central Site A
Modem
If either primary line fails, the modem at Central Site A
can connect to Router B or C via a backup circuit.
= Primary Line
= Backup Line
PSTN
Modem
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