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VPN phones causing UC540 to hit 100% cpu usage and call failure

alltraders001
Level 1
Level 1

This post is just so the community knows about what I have been working on. I consider the issue both interesting and closed.

For about three weeks we have worked with Cisco engineers to address call dropouts for our VPN phones. Calls typically dropped out between 30 seconds to 5 minutes in and this happened in over 80% of cases. We were able to see that internal VPN calls (calls from our VPN phones to other phones in different offices connected to our UC540) only had the issue less than 25% of the time. Calls to external numbers from non-VPN phones rarely failed if ever.

The engineer identified a CPU spike to 100% during our external VPN calls but even after hours of debugging could not identify the cause of the spike. However, when the spike happened, call quality deteriorated and the call became very unstable and eventually dropped. As the cause could not be identified and there were a few other small issues present in the system, we replaced the UC with an identical unit and tested again. Unfortunately, all issues occured on the replacement system just as they did on the original system. All firmwares were up to date. Everything is and was CCA compliant.

Whilst we couldn't identify the cause of the problem, an upgrade of the SPA525G2 phones solved the problem. We were using 7.4.9a firmware. The issue went away when we upgraded to 7.5.1(RC1). We don't know why but now our VPN calls work and previously they didn't.

1 Reply 1

David Trad
VIP Alumni
VIP Alumni

Hi Michael,

Interesting problem you had

I would have loved to seen the debug info on the VPN tunnel (SSL in this case I believe) versus the new phone firmware to see if there was a major reduction in chatter over the VPN link, there is a good chance that the previous firmware never created a clean connection and probably resulted in an increase in chatter which would then cause the UC to have to work harder.

Just a thought, but it is good to see it is resolved anyway

Cheers,

David.

Cheers, David Trad. **When you rate a persons post, you are indicating a thank you or that it helped, but at the same time you are also helping to maintain the community spirit - You don't have to rate posts and you wont be looked down upon :) *