Cisco Systems 7940G Manual De Usuario

Intermittent network outages affect data and voice traffic differently. Your network might have been 
experiencing intermittent outages without detection. If so, data traffic can resend lost packets and verify 
that packets are received and transmitted. However, voice traffic cannot recapture lost packets. Rather 
than retransmitting a lost network connection, the phone resets and attempts to reconnect its network 
connection.

If you are experiencing problems with the voice network, you should investigate whether an existing 
problem is simply being exposed. 

The following suggestions can help you determine if the phone has been properly configured to use 
DHCP:

Verify that you have properly configured the phone to use DHCP. See the 

 for more information.

Verify that the DHCP server has been set up properly.

Verify the DHCP lease duration. Cisco recommends that you set it to 8 days.

Cisco Unified IP Phones send messages with request type 151 to renew their DHCP address leases. 
If the DHCP server expects messages with request type 150, the lease will be denied, forcing the 
phone to restart and request a new IP address from the DHCP server.

If the phone has been assigned a static IP address, verify that you have entered the correct settings. See 
the 

 for more information.

If the Cisco Unified IP Phone appears to reset during heavy network usage (for example, following 
extensive web surfing on a computer connected to same switch as phone), it is likely that you do not have 
a voice VLAN configured.

Isolating the phones on a separate auxiliary VLAN increases the quality of the voice traffic. See the 

 for 

details.