“Network Busy” error on Cisco 7921G or 7925G IP Phone

I support wireless voice in multiple warehouses. These warehouses use the Cisco 7921G and the 7925G IP Phones. We started with the 7921Gs and moved to the 7925Gs when they became available. Many of the managers have become reliant on the use of these mobile IP Phones. As you can imagine, a warehouse is not the safest place for a mobile telephone. These phones often fall off of forklifts and golfs, unfortunately, I have to replace them more often then I would like.

Recently we made an order for some Cisco 7925G phones. I shipped four of them to the same location to replace broken phones. The onsite tech performed the initial configuration and added them to Cisco Unified Communications Manager (CUCM). I then received a call stating the new phones will not make a call and they give the following error “Network Busy”.

My first thought was Call Admission Control (CAC). I checked the phones to find that the location statement was wrong. I changed it and that didn’t resolve the issue. CUCM was not setup for CAC, all of the locations were given unlimited bandwidth between sites. I started looking into the CAC features on the wireless network. According to the configuration guides, everything looked correct.

After validating my configuration on CUCM and the Cisco 4404 Wireless LAN Controller (WLC), I decided to capture some debugs. Using the following debug command, I was able to figure out the issue.
debug cac all enable
I enabled the debug, then had the onsite tech try to make a call.

In the debug file, I did a search for deny, then fail.

I found the following fail entry.

*apfMsConnTask_0: Oct 30 14:28:40.566: 44:2b:03:55:FF:FF TSPEC from mobile (up = 6), Phy rate check failed.
*apfMsConnTask_0: Oct 30 14:28:40.566:
Not including un-operational rate 12 in TSRS IE

Phy rate check failed was the issue. The PHY is the minimum data rate that the phone will work at. This is a configurable item via the USB configuration through the phones web GUI. The phone was set to 12 Mbps, while the wireless network had a minimum data rate of 6 Mbps enabled. After changing the minimum PHY rate to 6 Mbps, the phone was able to make a phone call.

Minimum PHY Rate

Cisco 7925G IP Phone Network Profile Configuration

Everything pointed to a CAC issue, but the debug was the key to finding the problem with the data rates.

What issues have you had that resulted in a “Network Busy” error on the Phone?
Has anybody else found something other then CAC and the data rates to produce a “Network Busy” error on the IP Phone?
Has anybody run into this same issue?

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