Quantum and Evolution Series Installation and Operating Handbook
8-47
8.12.9.4.3 IEEE 802.1p Priority Tag
Classification may be done on the 3-bit Priority Code Point field of an IEEE 802.1q VLAN
tag (also referred to as an IEEE 802.1p Priority Tag). This is part of a 32-bit field inserted
into an Ethernet frame between the MAC address and length field.
The priority tag has eight possible values, each of which maps directly to an equivalent
internal class within the modem (for which a BIR, CIR, etc. can be set). Each packet
passed to the modem must have this field set to the appropriate value in order for the
modem to recognize the different data streams.
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Note that the modem includes support for IEEE 802.1p (priority tagging) as an alternative
QoS scheme to traffic shaping in its own right. In this case the packets must already be
tagged at the point of entry to the modem. It is a layer 2 feature that uses 8 classes of data
(3-bit field) to prioritise packets. The modem uses the tags to decide which packet to
transmit over satellite first when it has more than one packet to send.
Two modes are supported, namely Strict Priority Queuing and Fair Weighting Queuing:
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Strict priority queuing: packets are queued for transmission based solely on
their priority – highest will always be sent first.
