
40 Chapter 3 Installing IP telephones
P0937663 03.1
Telephone does not connect to system
If an IP telephone does not display the text
Connecting to server
within two minutes after
power up, the telephone was unable to establish communications with the Business
Communications Manager. Double check the IP configuration of the telephone, and the IP
connectivity to the Business Communications Manager (cables, hubs, etc.).
Slow connection
If the connection between the IP client and the Business Communications Manager is slow (ISDN,
dialup modem), change the preferred CODEC for the telephone from G.711 to G.729. See “IP
telephone server configurations” on page 37.
One-way or no speech paths
Signaling between the IP telephones and the Business Communications Manager uses Business
Communications Manager port 7000. However, voice packets are exchanged using the default
RTP ports 28000 through 28255 at the Business Communications Manager, and ports 51000
through 51200 at the IP telephones. If these ports are blocked by the firewall or NAT, you will
experience one-way or no-way speech paths.
Dropped voice packets
If the LAN traffic in your network environment is heavy, you may experience dropped voice
packets. If this occurs, connect the Business Communications Manager and the telephones to a
local network hub to avoid the network traffic.
The IP telephone monitors the number of incoming voice packets that arrive every five seconds
during a call. If the number of packets becomes less than expected, the user will receive either
broken transmissions or silence. The telephone will display an
INCOMING PACKET LOSS
message for three seconds. If the message is transitory, there is no concern. If the message appears
continuously, it indicates that the voice packets from the sending telephone are not properly
routing over the network. Check the configuration settings of any NAT server, DHCP server,
firewall, and router between the telephone and the sending telephone.
Changing the contrast level
When an IP telephone is connected for the first time, the contrast level is set to the default setting
of 1. Most users find this value is too low. Therefore, after the telephone is operational, you can
increase the contrast level by pressing
Fe a t u r e
•‡ at the telephone.
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