IEEE 802.1D and 802.1Q

IEEE’s 802.1Q standard defines a tag that can be added to voice and data packets. Most of the information associated with this tag deals with Virtual LAN (VLAN) management, but 3 bits are reserved for identifying packet priority. These 3 bits allow any one of 8 priorities to be assigned to a specific packet. As defined in the standard, the 8 priorities are, from highest to lowest:

• 7: Network management traffic
• 6: Voice traffic with less than 10ms latency
• 5: Voice traffic with less than 100ms latency
• 4: “Controlled-load” traffic (mission-critical data applications)
• 3: Traffic meriting “extra-effort” by the network for prompt delivery (for example, executives’
      e-mail)
• 2: Reserved for future use
• 0: Traffic meriting the network’s “best-effort” for prompt delivery (the default priority)
• 1: Background traffic such as bulk data transfers and backups

  NOTE:

  Priority 0 is a higher priority than Priority 1.

To support IEEE 802.1D/Q, the 4600 Series IP Telephones can be administered either from the network via appropriate administration of the DHCP or TFTP servers, or at the telephone itself via dialpad input. Specific implementation details for local administration are in the Installation Guide, and for remote administration are in this chapter, in 4600 Series IP Telephone Scripts and Application Files. In summary, four IEEE 802.ID/Q QoS parameters in the telephones can be administered. These parameters are:

• L2QVLAN: setting the VLAN ID on which the telephone should operate. For example, what VLAN ID to use for DHCP Discovery, etc. (up to 4 digits, from 0 to 4094, default is 0).
• VLANTEST: setting the number of seconds to wait for a DHCPOFFER when using a non--zero VLAN ID (up to 3 digits, from 0 to 999, default is 60).
• L2QAUD: setting the 802.1Q audio priority value (between 0 and 7, default is 6)
• L2QSIG: setting the 802.1Q signaling priority value (between 0 and 7, default is 6)

In the 4600 Series IP Telephone Installation Guide, the Local Administrative Option for specifying ADDResses also allows you to specify VLAN IDs and VLANTEST values (see also VLAN Considerations). The Local Administrative Option for specifying QoS values allows you to specify values for L2QAUD and L2QSIG.

The 4600 Series IP Telephones can simultaneously support receipt of packets using, or not using, 802.1Q parameters.