130 | Managing the Radio
Aprisa SRx User Manual 1.3.0
PRIORITY DEFINITIONS
PCP (Priority Code Point)
These settings provide priority translation / mapping between the external radio LAN VLAN priority
network and the radio internal VLAN priority network, using the VLAN tagged PCP (Priority Code Point)
priority field in the Ethernet/VLAN frame.
The IEEE 802.1Q specification defines a standards-based mechanism for providing VLAN tagging and class
of service (CoS) across Ethernet networks. This is accomplished through an additional VLAN tag, which
carries VLAN tag ID and frame prioritization information (PCP field), inserted within the header of a Layer
2 Ethernet frame.
Priority Code Point (PCP) is a 3-bit field that indicates the frame priority level (or CoS). The operation of
the PCP field is defined within the IEEE 802.1p standard, which is an extension of 802.1Q. The standard
establishes eight levels of priority, referred to as CoS values, where CoS 7 (‘111’ in PCP filed) is the
highest priority and CoS 0 (‘000’) is the lowest priority.
The radio in bridge mode used the PCP value in the VLAN tag to prioritize packets and provide the
appropriate QoS treatment per traffic type. The radio implements 4 priority queuing techniques that base
its QoS on the VLAN priority (PCP). Based on VLAN priority bits, traffic can be put into a particular Class of
Service (CoS) queue. Packets with higher CoS will always serve first for OTA transfer and on ingress/egress
Ethernet ports.
The ‘PCP priority definition’ tab is used to map ingress VLAN packet with PCP priority to the radio internal
CoS (priority). Since, in most of the cases the radio VLAN network is connected to the corporate VLAN
networks, the network administrator might like to have a different VLAN priority scheme of the radio
network CoS. For example, management traffic in the multi-gigabit corporate VLAN network might be
prioritize with priority 7 (highest priority) and SCADA traffic with priority 5, but in the narrow bandwidth
radio network, SCADA traffic will be map to radio very high CoS / priority (i.e. set PCP 5 = Very high) and
management traffic might will be map to radio medium CoS / priority (i.e. set PCP 7 = medium) in order
to serve first the mission-critical SCADA traffic over the radio network.
