Section 3: ISDN (4 Points)
If your Frame Relay network fails, allow R4 to dial into R1. Use passwords that are difficult to detect. Ensure R4 dials out after 5 seconds of Frame Relay failure. If the Frame Relay network restores, keep the call connected for a further 45 seconds before disconnecting. OSPF is required over the ISDN network when a call is established. Do not configure any Layer 3 addressing on the physical ISDN interfaces.
You only have one option here and you are given plenty of clues; you need to use the backup interface solution with the delay configured to meet the timing requirements. You only need to configure a backup interface on R4 as R1 is not required to dial into R4; therefore you can simply omit a dialer string on R1. ...
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