Cisco 7937G Administration Guide - Page 100

General Troubleshooting Tips Chapter 9 Troubleshooting and Maintenance Table 9-1 Cisco Unified IP Conference Station 7937G Troubleshooting (continued) Summary Loopback condition Moving a network connection from the conference station to a workstation Explanation A loopback condition can occur when the following conditions are met: • The conference station receives power from an external power supply • The conference station is powered down (the power supply is disconnected) In this case, the switch port on the conference station can become disabled and the following message will appear in the switch console log: HALF_DUX_COLLISION_EXCEED_THRESHOLD To resolve this problem, re-enable the port from the switch. If you are powering your conference station through the network connection, you must be careful if you decide to unplug the conference station's network connection and plug the cable into a desktop computer. No dial tone No LCD screen display One-way audio 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 conference station before plugging it into a computer. This delay gives the switch enough time to recognize that there is no longer a conference station on the line and to stop providing power to the cable. Check that all connections are secure and in place. Make sure all connections are correct. Check to make sure that the conference station has power. Make sure that the power supply unit is plugged in. When at least one person in a call does not receive audio, IP connectivity between conference stations is not established. Check the configurations in routers and switches to ensure that IP connectivity is properly configures. 9-10 Cisco Unified IP Conference Station 7937G Administration Guide for Cisco Unified Communications Manager 6.0 OL-11560-01 Rev. B0