Cisco Systems 6921 manual Summary Explanation, Locking Options section on page 4-3 for details

Chapter

General Troubleshooting Tips

Table 9-2	Cisco Unified IP Phone Troubleshooting
Summary		Explanation
Connecting a Cisco Unified IP Phone to		Cisco does not support connecting an IP phone to another IP phone through the
another Cisco Unified IP Phone/		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.
Poor quality when calling digital cell		In Cisco Unified Communications Manager, you can configure the network to
phones using the G.729 protocol.		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.
Prolonged broadcast storms cause		A prolonged Layer 2 broadcast storm (lasting several minutes) on the voice
IP phones to reset, or be unable to make or		VLAN may cause IP phones to reset, lose an active call, or be unable to initiate
answer a call.		or answer a call. Phones may not come up until a broadcast storm ends.
Moving a network connection from the		If you are powering your phone through the network connection, you must be
phone to a workstation.		careful if you decide to unplug the phone’s network connection and plug the
		cable into a desktop computer.
		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.
Changing the telephone configuration.		By default, the network setup options are locked to prevent users from making
		changes that could impact their network connectivity. You must unlock the
		network setup options before you can configure them. See the “Unlocking and
		Locking Options” section on page 4-3for details.
Phone resetting.		The phone resets when it loses contact with the Cisco Unified Communications
		Manager software. This lost connection can be due to any network connectivity
		disruption, including cable breaks, switch outages, and switch reboots.
LCD display issues.		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.
Dual-Tone Multi-Frequency (DTMF)		When you are on a call that requires keypad input, if you press the keys too
delay.		quickly, some of them might not be recognized.
Codec mismatch between the phone and		The RxType and the TxType statistics show the codec that is being used for a
another device.		conversation between this Cisco Unified IP phone and the other device. The
		values of these statistics should match. If they do not, verify that the other
		device can handle the codec conversation, or that a transcoder is in place to
		handle the service.
		See the “Call Statistics Screen” section on page 7-8for information about
		displaying these statistics.

	Cisco Unified IP Phone 6921, 6941, 6945, and 6961 Administration Guide for Cisco Unified Communications Manager 8.5 (SCCP and SIP)
9-10	OL-23769-01