Specifications

Engineering Guidelines
234
Since these values are non-user programmable they cannot be changed by the system
administrator. These values do not provide the correct priority levels for voice media at either
L2 or L3, therefore the use of these values will potentially cause severe voice quality issues.
The Solutions:
1. If it is a requirement to keep LLDP-MED running on the Cisco switches:
• Leave LLDP-MED running on the Cisco switches.
• Use DHCP to provide the phones with the correct L2 and L3 priority settings.
DHCP learnt values have a higher priority and will override the LLDP-MED learnt values.
2. In situations where there is no requirement to have LLDP-MED and CDP running on the
Cisco switches:
• Disable LLDP-MED on the Cisco switches.
• Disable CDP on the Cisco switches.
• Use DHCP with double fetches to provide the phones with the correct L2 and L3 priority
settings. Information on DHCP double fetches can be found under “DHCP and IP Phone
network policy” on page 235“.
3. If there is no requirement to keep LLDP-MED running on the Cisco switches:
• Disable LLDP-MED on the Cisco switches.
• Enable CDP to provide the phones with VLAN information.
• When the phones detect that CDP is present on the LAN they will infer that the ‘default
Cisco values’ for L2 and L3 priority should be used.
The Cisco default values for priority are:
• L2 (802.1p) = 5
• L3 (DSCP) = 46
LAN policy values for media, signalling and other
The System Administrator has a high degree of flexibility when deciding on how to program
LAN Policy.
LAN Policy values for signalling and voice can be programmed independently, or signalling and
voice can both be programmed with the same set of values.
Other data that might exist on the same network, or VLAN, as voice include management data
and downloads. This data is classified as ‘other’, as it is part of the solution, but not immediately
needed for real-time call handling.
For backwards compatibly with controllers running earlier software, both voice and signalling
should use a DSCP value of 46 and an IEEE 802.1p value of 6.
Note: The inferred Cisco L2 and L3 values used by the phone are not permanent, these
values can be overwritten with installer defined DHCP values.