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Feedback?This Help article is for Cisco Wireless Phone 9821 registered to Cisco Unified Communications Manager (Unified CM).
If users report that when they are engaged in an active phone call and walking from one location to another (roaming), the voice quality deteriorates or the connection is lost, use the information in this section to identify the cause of the problem.
Voice quality deteriorates while roaming
Problem
User complains that the voice quality deteriorates while roaming.
Solution
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Check the RSSI on the destination access point to see if the signal strength is adequate. The next access point should have an RSSI value of -67 dBm or greater.
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Check the site survey to determine if the channel overlap is adequate for the phone and the access point to hand off the call to the next access point before the signal is lost from the previous access point.
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Check to see if noise or interference in the coverage area is too great.
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Check that signal to noise ratio (SNR) levels are 25 dB or higher for acceptable voice quality.
Voice conversation delays while roaming
Problem
User complains of delays in the voice conversation while roaming.
Solution
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Check the Neighbor List to see if there is another acceptable access point as a roaming option. The next access point should have an signal of -60 dBm to roam successfully.
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Check the Cisco Catalyst 45xx switch. If Cisco Catalyst 45xx series switches are being used as the main Layer 3 switches in the network, ensure that the supervisor blades are a minimum SUP2+ or later version. The wireless phone (or any wireless client) experiences roaming delays when an earlier version (SUP 1 or SUP2) blade is used.
Phone loses Cisco Unified CM connection while roaming
Problem
User complains that the call gets dropped while roaming.
Solution
Check for the following configuration or connectivity issues between the phone and the access point:
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The RF signal strength might be weak. Access the Neighbor list and check the RSSI value for the next access point.
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The next access point might not have connectivity to Cisco Unified CM.
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There might be an authentication type mismatch between the phone and the next access point.
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The access point might be in a different subnet from the previous access point. Cisco Wireless Phone 9821 is capable of Layer 2 roaming only. Layer 3 roaming requires WLSM that uses GRE. For more information, see WLANs and roaming.
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If using EAP-FAST, EAP-TLS, or EAP-PEAP authentication, the access point might be using filters to block TCP ports. The RADIUS server uses port 1812 for authentication and 1813 for accounting.
Phone does not roam back to preferred band
Problem
The phone does not roam back to the preferred wireless band.
Solution
For troubleshooting information, see the Cisco Wireless Phone 9821 depoyment guide.
