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Quantum and Evolution Series Installation and Operating Handbook
7.4.4
Interface Configurations
Interface Configuration Screen
Quality of Service is based on IEEE 802.1p priority tagging. It uses a 3-bit field within
the VLAN tag as a means of prioritising packets. The modem responds to the priority
level set in the VLAN tag when the packet is received.
The default is to use strict priority queuing, where three queues are established, with
the highest priority (level 7) being sent first followed by the medium priority (levels 6 and
5) and finally packets from the low priority (levels 4 to 0) queue. However, if there is a
large amount of high priority traffic this can have the effect of starving bandwidth for lower
priority traffic.
Selecting Weighted QoS enables fair-weighted queuing. This applies a weighting to the
three traffic queues where the highest priority data gets most bandwidth, but bandwidth is
reserved for other lower priority data; for every 4 packets sent from the high priority
queue, 2 are sent from the medium priority queue and 1 from the low priority queue.
The modem supports IEEE 802.1q VLAN tagging. If Ethernet frames with VLAN tags are
presented to the modem when in bridge mode then these packets will be transmitted
transparently along with the VLAN tags. VLAN filtering can also be used with point-to-
multipoint topology to separate traffic flows as long as there is a return path. In point-to-
multipoint operation, each remote modem receives all of the data and use of VLAN tags
over just the satellite portion of he link is a useful way of being able to filter out unwanted
traffic at the remotes. A VLAN id is assigned by the user to each remote modem. The hub
Tx modem automatically learns what VLAN tags are associated with each remote. It also
learns the location of every device connected to each remote. As data is received at the
hub, the Tx modem adds a VLAN tag with the id of the remote for which it is destined. At
the remote, unwanted data is filtered out and discarded. The VLAN tag is also removed
from wanted packets that have been received at the remote before they are forwarded
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