Operation Manual – Voice VLAN
H3C S3100 Series Ethernet Switches Chapter 1 Voice VLAN Configuration
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When an IP phone applies for an IP address from a DHCP server, the IP phone can
also apply for the following extensive information from the DHCP server through the
Option184 field:
z IP address of the network call processor (NCP)
z IP address of the secondary NCP server
z Voice VLAN configuration
z Failover call routing
Following describes the way an IP phone acquires an IP address.
Figure 1-1 Network diagram for IP phones
As shown in
Figure 1-1, the IP phone needs to work in conjunction with the DHCP
server and the NCP to establish a path for voice data transmission. An IP phone goes
through the following three phases to become capable of transmitting voice data.
1) After the IP phone is powered on, it sends an untagged DHCP request message
containing four special requests in the Option 184 field besides the request for an
IP address. The message is broadcast in the default VLAN of the receiving port.
After receiving the DHCP request message, DHCP Server 1, which resides in the
default VLAN of the port receiving the message, responds as follows:
z If DHCP Server 1 does not support Option 184, it returns the IP address assigned
to the IP phone but ignores the other four special requests in the Option 184 field.
Without information about voice VLAN, the IP phone can only send untagged
packets in the default VLAN of the port the IP phone is connected to. In this case,
you need to manually configure the default VLAN of the port as a voice VLAN.
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