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QoS
Issue 2.2 April 2005 75
To support IEEE 802.1D/Q, the 4600 Series IP Telephones can be administered either of two
ways:
● from the network by appropriate administration of the DHCP or TFTP/HTTP servers, or
● at the telephone itself using dialpad input.
Specific implementation details for local administration are in the Installation Guide. This
chapter covers remote administration in 4600 Series IP Telephone Scripts and Application
Files on page 67. In summary, five IEEE 802.ID/Q QoS parameters in the telephones can be
administered. These parameters are:
● L2Q: setting the 802.1Q framing parameter (1=ON, 2=OFF, or 0=AUTO. The default is 0.)
You can manually set a specific 4600 IP Telephone’s L2Q value to any value other than
AUTO, for example to ON or OFF. However, the telephone uses that manual value rather
than any value administered via the DHCP or TFTP/HTTP settings file. To use the QoS
Local Administrative Option to set L2Q manually see the 4600 Series IP Telephone
Installation Guide.
● 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
on page 79. The Local Administrative Option to specify QoS values
allows you to specify values for L2Q, L2QAUD, and L2QSIG.
The 4600 Series IP Telephones can simultaneously support receipt of packets using, or not
using, 802.1Q parameters.
DIFFSERV
IETF RFCs 2474 and 2475 define “services” basically as different ways to treat a network’s
different traffic subsets at the Internet Protocol (IP) layer, Layer 3. For example, some packets
might be routed to expedite delivery and minimize delay, with other packets routed to minimize
loss or cost. Redefining an octet in the Layer 3 headers for IP versions 4, or IPv4 and 6, or IPv6
provides the differentiation between these services (Differentiated Services). IPv4 calls this
octet a Type of Service (TOS) octet while IPv6 calls this octet a Traffic Class. In both cases, the
octet is interpreted differently than it was originally defined. With Differentiated Services, bits 0
through 5 of the octet identify a Differentiated Services Code Point (DSCP). The DSCP
identifies a procedure to be used to handle that packet on a per-hop basis. Bits 6 and 7 of the
octet are currently unused, and DSCP-compliant routers ignore them.