User's Manual

Horizon Compact Plus Release 1.0.1 Wireless Ethernet Product User Manual – Volume 2
8.0 Quality of Service (QoS)
QoS implementation is best done on the ingress and egress portions of the transport network. As such,
QoS should be implemented on the Ethernet switches. Once that implementation is in place, the Horizon
Compact Plus can be configured for QoS, should the potential for congestion exist.
The Horizon Compact Plus has two physical GigE ports (10/100/1000 Base-T). Each port can also be
independently reconfigured as two fast Ethernet ports (10/100 Base-T). Incoming packets from each port
are multiplexed into a single stream, with port identifiers added to each packet. Several different types of
packet are supported.
8.1 Class of Service Types
Enabling QoS on Horizon Compact Plus (set qos [on|off]) ensures that incoming packets are handled
with a priority based on the Class of Service (CoS) bits embedded in several types of data packet. Each
port can be independently configured for the type of data packet it is to process. Either VLAN (802.1p)
packets, Super VLAN (Q-in-Q, or double tagged) packets, or the DSCP field in IPv4 and IPv6 packet
headers, and MPLS EXP can be selected.
For Super VLAN (or Q-in-Q) packets, since a standard VLAN packet is encapsulated within the Super
VLAN packet, there may be two sets of CoS bits associated with the Super VLAN packet. One will be the
CoS bits of the encapsulated, or inner, VLAN frame (usually associated with the “customer”) and the
other will be the CoS bits of the Super VLAN packet itself, or outer, header (usually associated with the
“service provider”).
The Horizon Compact Plus can be configured to use the CoS bits of either, Super VLAN inner
(cos_qinq_itag), or outer (cos_qinq_otag), packets, or the CoS bits of the standard VLAN, or DSCP bits,
or MPLS EXP.
To determine the type of packets on which you wish the packet filter to operate you need to configure the
CoS type (set cos type [cos_vlan|cos_qinq_itag|cos_qinq_otag|cos_dscp|cos_mplsexp]) for each
port.
8.2 Class of Service Bit Levels
The CoS bits have a derived numeric value ranging from 0 to 7, giving eight CoS priority levels. Network
administrators can allocate CoS levels to data packets in order to prioritize the types of traffic. The higher
the level, the higher the priority of the packet. For example, video, or VoIP traffic needs to be handled with
minimal delay, whereas simple data traffic can tolerate delays in getting to its destination. For this
example the video or VoIP packets will be allocated a higher CoS level than that of the data traffic.
8.3 Operation with QoS Disabled
If QoS is disabled in the Horizon Compact Plus system, all incoming user data packets are treated
equally and are forwarded on a first-come first-served basis. The system operates on a first-in-first-out
(FIFO) basis.
If the Pause Frames feature is enabled, pause frames will be sent to the connected switch when the input
buffer is close to being full (internally set threshold). This allows time for the queue to empty prior to more
frames being received and thus avoids congestion.
When QoS is enabled, the pause frame feature is not available.
By default, control frames, or slow bridge protocol packets, are always directed to a high priority buffer,
ensuring that this type of traffic always has the highest priority compared with that of user data traffic.