Cisco 7961G Administration Guide - Page 221
Summary, Explanation, Dual-Tone Multi-Frequency
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Chapter 9 Troubleshooting and Maintenance General Troubleshooting Tips Table 9-2 Cisco Unified IP Phone Troubleshooting (continued) Summary Prolonged broadcast storms cause IP phones to reset, or be unable to make or answer a call. Moving a network connection from the phone to a workstation. Explanation A prolonged Layer 2 broadcast storm (lasting several minutes) on the voice VLAN may cause IP phones to reset, lose an active call, or be unable to initiate or answer a call. Phones may not come up until a broadcast storm ends. If you are powering your phone through the network connection, you must be careful if you decide to unplug the phone's network connection and plug the cable into a desktop computer. Changing the telephone configuration. Phone resetting. LCD display issues. Dual-Tone Multi-Frequency (DTMF) delay. Caution The computer's network card cannot receive power through the network connection; if power comes through the connection, the network card can be destroyed. To protect a network card, wait 10 seconds or longer after unplugging the cable from the phone before plugging it into a computer. This delay gives the switch enough time to recognize that there is no longer a phone on the line and to stop providing power to the cable. By default, the network configuration options are locked to prevent users from making changes that could impact their network connectivity. You must unlock the network configuration options before you can configure them. See the "Unlocking and Locking Options" section on page 4-4 for details. The phone resets when it loses contact with the Cisco Unified CallManager software. This lost connection can be due to any network connectivity disruption, including cable breaks, switch outages, and switch reboots. If the display appears to have rolling lines or a wavy pattern, it might be interacting with certain types of older fluorescent lights in the building. Moving the phone away from the lights, or replacing the lights, should resolve the problem. When you are on a call that requires keypad input, if you press the keys too quickly, some of them might not be recognized. Cisco Unified IP Phone 7961G/7961G-GE and 7941G/7941G-GE Administration Guide for Cisco Unified CallManager OL-11528-01 9-15