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Serial interface resets and carrier transitions

Hi all tech-guys,

Well I'm facing a typical problem with my Cisco router, connected to my local ISP (Telco), with the WAN lease line of 64 Kbps internet connection of 2 pair copper wire (one actual pair in use and other as standby pair). Although my router and lease line modem pairs one at my location and the other modem at the ISP location are redundantly backed up with the standard UPS power supply. So whenever there is a break in the power supply, immediately we loose the Line protocol link activity with the remote ISP link, which i usually monitor on the modem front panel LED indications as follows,

Power=On, RTS=On, TD=Off, RD=Off, DCD=Off, LOS=toggles with Red color indication and later resumes to Off normally, and after momentarily the above said TD, RD and DCD link activity resumes normally, i.e. Line protocol comes up. But when i contact our carrier service provider for the above said problem, they deny about their technical faults. To add one more point to the said story is that the lease line laid by our Telco is not directly connected point-to-point connection, whereas there is one more intermediate Telco's branch exchange through which our lease circuit is

splitted and reconnected directly to my office premises, the said intermediate exchange falls in our same local area, so whenever there are any power failures the intermediate Telco is also affected by the power loss, but the Telco says that they have immediate switchover power supply to their virtual circuits. So please consider my query and give me a good handful solution as i have installed two separate built-in battery UPS of 500VA backup support or do we need to upgrade for Online UPS? And when i monitor my router for the sh int serial 0 i see the "1 interface resets, 2 carrier transitions" as we use the internet to run mission critical remote applications stored in remote terminal server, if the internet line protocol is interrupted then we face user account lockouts due to uneven session logout. So please do consider. I'm very thankful to your suggestions replied.


Vinayak Killekar

System Administrator

VIP Purple

Re: Serial interface resets and carrier transitions


I am not sure if I fully understand your question, but any UPS (online or offline) will not help you protect against interface resets or carrier transitions. If the power problem is at your side, your router would reboot, and I guess that is not the case ? My experience with Telcos is that they almost always deny any failure on their equipment, simply because it happens so often that they do not have the means to look into every single incident.

Check the following link for a good explanation of interface resets and carrier transitions:

Troubleshooting Serial Lines