Nov 05

“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?

Jun 06

Wireless Voice in a Warehouse on a golf cart

Wireless Voice in a Warehouse on a golf cart is very difficult to get working well.

I have found it very difficult to get the Cisco 7921G wireless phones to be reliable in a warehouse with shelving and product to the ceiling. Employee’s riding golf carts while using the phones add to the challenge.

Here are a few tips and tricks to get it to work.

1. Every drive aisle needs to have line of site to an access point, or constant roaming from AP to AP will cause the voice to drop out.
2. Where possible, lower the AP as low as it can go while still being above the client.
a. Place AP’s below Drop Ceilings
b. If in open area, fabricate a bracket to lower it closer to the ground.
3. Have all of the AP’s in a section on the same controller if there are multiple controllers. For Example: All of building 1’s AP’s should be on the same controller.
4. Use 8 channels, configure the Cisco 7921G to only scan those 8 channels. (This is very important)
a. 36,40,44,48,149,153,157,161
5. Use RRM for channel allocation.
6. Set the power level to 1 on the 5GHz radios (Full Power).
7. In open areas, do not over populate AP’s. Too many possible AP’s to roam to with similar signal strengths can cause roaming issues. The phone works best if it can connect to an AP and stay on it for a while.
8. Make sure your controllers are configured for roaming between each other. If this is not setup, the phone will drop every time it roams to an AP on the other controller.
9. Data Rates to use with voice over wireless (WVOIP)
a. Disable 6,9, 48,54
b. Mandatory 12, 36
c. Supported 18,24
10. Enable Client Link

Don’t forget to configure QOS on the wired network. Here are some example configurations on Cisco Switches that may help you.

I would like to know other things to change to make wireless VOIP work getter in this type of environment.

Please let me know if this has helped you or if you have any other suggestions for me.