We as engineers spend a lot of time troubleshooting circuits that are down. These are my troubleshooting steps and I use the checklist for when the carrier says it’s a customer issue and not their equipment.
I like to start at physical layer and work my way up the OSI model.
- Check the smartjack. Is it all green? If not check the amber leds and notify the carrier which ones are amber.
- Check the cable between the smartjack and the router. If the carrier extended the circuit this is their responsibility, but since we want the circuit up ASAP I test it.
- Loopback the card (T1/T3/whatever). This will tell us if the card is good. We should have all green led’s on the card.
- Swap the WAN card if possible
- Put the WAN card in another slot (this has never resolved an issue for me, but I do it anyway)
- Check the logs (probably already have)
- Check the interface statistics. Look for CRC errors and input/output drops
- Check the clocking on the line
- Double check the lincode and framing
- Check for increasing errors on the controller
- Reboot the router. I hate doing this but I have seen where a carrier will move the T1 to a new card on their side and a reboot of my router is needed.