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Network design
An IP Telephone and an attached PC on the same VLAN
Three variations exist for attaching a personal computer to the telephone. The first two involve
having both the telephone and the computer on the same VLAN, which is the port VLAN or the
native VLAN. Refer to the IP Telephony Implementation Guide for a primer on VLANs. In the
first scenario, traffic from both the telephone and the PC have no CoS tagging. In this case, no
special configurations are necessary. Just attach the telephone to an access port (one with only
the port VLAN or the native VLAN configured), and attach the computer to the telephone.
The second scenario is similar to the first, except that traffic from the telephone is tagged with
Layer 2/Layer 3 priority while remaining on the port VLAN or the native VLAN. The telephone
must be configured to tag its Ethernet frames and/or IP packets with the desired priority. This is
normally set by DHCP or TFTP by specifying the following parameters:
802.1Q. On/off for 802.1Q tagging. Turn this on if Layer 2 priority tagging is desired.
Otherwise, turn this off.
L2 audio. Layer 2 CoS tag for Ethernet frames that contain audio packets. Set this to a
value between 0 and 7. This value is sent to the telephone by Avaya Communication
Manager, as configured on the IP Network Region form.
L2 signaling. Layer 2 CoS tag for Ethernet frames that contain signaling packets. Set this
to a value between 0 and 7. This value is sent to the telephone by Avaya Communication
Manager, as configured on the IP Network Region form.
LAN ID. Must be set to zero (0) for this scenario. A VID of zero indicates that the Ethernet
frame belongs on the port VLAN or native VLAN. The VID has no effect when 802.1Q
tagging is disabled. Cajun switches require no special configuration for this scenario.
Cisco switches, however, behave differently for different hardware platforms and OS
versions.
test results on a sample of hardware platforms and OS versions.
L3 audio. Layer 3 DSCP for audio IP packets. Set this to a value between 0 and 63. This
value is sent to the telephone by Avaya Communication Manager, as configured on the IP
Network Region form.
L3 signaling. Layer 3 DSCP for signaling IP packets. Set this to a value between 0 and 63.
This value is sent to the telephone by Avaya Communication Manager, as configured on
the IP Network Region form.
Remember that for the CoS tags to have any effect, the corresponding QoS configurations must
be implemented on the necessary network devices. Remember also that improperly enabling
Layer 2 and Layer 3 tagging can break processes that were working without tagging.
Service guidelines
296 Avaya Application Solutions IP Telephony Deployment Guide
Table 70: Cisco hardware characteristics
contains more information on CoS and QoS.
on page 289 shows Avaya laboratory
Quality of
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