Specifications

Network Configuration Concepts
217
In a Cisco based environment the recommended settings are:
• Voice Packets: DSCP: 46, 802.1p:5
• Signalling Packets: DSCP: 26, 802.1p:3
• Other Packets: DSCP:0 802.1p:0
For Cisco based environments refer to “Network QoS settings in a Cisco Environment” on
page 248.
LAN QoS policies
The 3300 can apply different LAN QoS policies to voice packets, signalling packets and other
packets. The LAN Policy (QoS) form in ESM is used for setting the LAN QoS policy values.
Refer to “LAN policy values for media, signalling and other” on page 234.
TOS-to-COS (IEEE 802.1p) mapping and softphones
In a converged environment with voice and data traffic on the network, some form of priority
mechanism should be used. If a voice device is resident on a data device, it may not be possible
to separate the traffic to independent network interfaces. In this case it is likely that both voice
and data appear from the same IP address and within the same subnet. This is the situation
for a softphone running on a PC.
Often the PC does not support VLAN, although it may support priority. Be careful with this
setting, since the VLAN tagging is added and the VLAN 0 is used. Different vendors treat VLAN
0 in different ways. If operation cannot be determined it is better to treat the PC as non-VLAN
aware and let the Layer 2 switch tag this with the Default or Native VLAN settings. For
non-VLAN-aware PCs, the only form of priority identification is from within the voice application.
The Type-of-Service field is set by this application on the PC. To get the correct VLAN priority,
configure the access port in the network to map this Type-of-Service (TOS) information, either
precedence or DSCP, to a VLAN priority (COS). Voice is still on the same subnet (and
native/default VLAN) as the data, but where priority schemes exist, the voice is treated ahead
of data.
Note that certain releases of Windows will overwrite the DSCP value that might be set within
an application and force both voice and data to DSCP 0. In this case the network equipment
may need to re-classify the DSCP values based on data type, such as UDP or RTP, or use of
TCP and UDP ports. See “3300 IP Ports” on page 271 for more details on ports used by the
phone.
On certain combined Layer 2 and Layer 3 switches, the ports may prioritize data based on
either COS or TOS/Diffserv data. This may also force a change (unexpectedly) in the COS to
TOS mapping information based on internal mapping rules. Usually these can be reconfigured
as necessary.
Note: COS is Class Of Service (IEEE 802.1p), not to be confused with the telecom Class
of Service value.