Cisco 7970G Administration Guide - Page 249

Chapter 9 Troubleshooting and Maintenance General Troubleshooting Tips General Troubleshooting Tips Table 9-2 provides general troubleshooting information for the Cisco Unified IP Phone. Table 9-2 Cisco Unified IP Phone Troubleshooting Summary Daisy-chaining IP phones Poor quality when calling digital cell phones using the G.729 protocol Prolonged broadcast storms cause IP phones to reset, or be unable to make or answer a call Explanation Cisco does not support connecting an IP phone to another IP phone through the PC port. Each IP phone should directly connect to a switch port. If phones are connected together in a line (by using the PC port), the phones will not work. In Cisco Unified Communications Manager, you can configure the network to use the G.729 protocol (the default is G.711). When using G.729, calls between an IP phone and a digital cellular phone will have poor voice quality. Use G.729 only when absolutely necessary. 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. Cisco Unified IP Phone 7970G/7971G-GE Administration Guide for Cisco Unified Communications Manager 6.1 OL-14626-01 9-15