Page 238 of 910 Features
553-3001-365 Standard 4.00 August 2005
The following describes the IP Phone support for 802.1Q.
DHCP requirements
Some implementation requirements of the Automatic VLAN Discovery using
DHCP are:
1A DHCP server IP address pool must exist for each subnet (also
VLANs). This is standard DHCP operation. The requirement is the same
for PCs or IP Phones.
2A DHCP server should not exist in more than one VLAN at one time (one
subnet for each VLAN), unless the link to the DHCP server is tagged and
the DHCP server can recognize this. With an untagged link to the DHCP
server, traffic could originate on one VLAN and end up on the other
VLAN. In this case, the VLAN using DHCP feature does not work.
Step Action
1If 802.1Q is disabled, standard Ethernet frames are transmitted.
2If 802.1Q is enabled, all frames transmitted by the Ethernet driver have the 802.1Q tag
bytes inserted between the source MAC address and the protocol type field. The tag
protocol identifier field contains 8100 (hex) and the CFI bit is set to 0.
3When 802.1Q is enabled, separate voice and data VLANs can be configured. Each
VLAN has its own ID and priority on the IP Phone. Voice packets have the priority bits
of all frames set to 6 (octal) and the VOICE VLAN ID is set to 000 (hex) by default. Data
packets have the priority bits of all frames set to 0 and the DATA VLAN ID is set to 000
(hex) by default. The GUI and TPS configured values override these values.
4The IP Phone’s Ethernet driver receives any Ethernet frame destined for it, regardless
of whether 802.1Q is enabled or the received frame is an 802.1Q tagged frame.
Note: The only exception is any 802.1Q tagged frame with CFI = 1. In this case, the
frame is discarded.
5The IP Phone’s Ethernet driver strips the 802.1Q tag information from the frame before
passing it on to the IP stack.
6The IP Phone’s Ethernet driver filters the packets by the VLAN tag and MAC address.
Tagged traffic is prioritized and routed based on the priority bits.