CoS (Class of Service) Basics

qos_ug.pngThe ePMP system features a QoS Classification Rules table which allows operators to configure Layer 2 and Layer 3 rules for prioritizing certain types of traffic over the wireless link.  

The QoS Classification Rules table contains all of the rules enforced by the device when passing traffic over the radio link. Traffic passed through the device is matched against each rule in the table; when a match is made the traffic is sent over the radio link using the priority defined in column Traffic Priority.

One type of Layer 2 rule is:

CoS:  Class of Service; traffic prioritization is based on the 3-bit header present in the 802.1Q VLAN-tagged Ethernet frame header in the packet entering the AP or SM Ethernet port.

This type of classification can be use to assign a LowHigh, or Voice priority to a traffic type (for example, voice, video, file transfer) ingressing the radio's Ethernet port to ensure that delivery of the packets is given precendence, especially when the link is running at near-to or full capacity.  

Where other QoS rule types (VLAN ID, EtherType, IP, MAC) allow operators to set priority levels for specific network segments, protocols, or devices, the CoS type allows for a broader method of classifying traffic based on the packets' payload type.  This broader type of categorization is useful especially when using wireless links to bridge network segments carrying delivery-speed sensitive data (for example, bridging two networks which utilize VoIP or video conferencing).  In these cases, good user experience is paramount and careful attention must be given to how this traffic is prioritized relative to lower-priority traffic.