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Chapter 7: Quality of Service (QoS) QoS Overview
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QoS Overview
Quality of Service (QoS) deals with the way frames are handled within the switching fabric. QoS is required in order
to deal with many different network scenarios, such as traffic congestion, packet availability, and delay
restrictions.
PTP 850’s personalized QoS enables operators to handle a wide and diverse range of scenarios. PTP 850’s smart
QoS mechanism operates from the frame’s ingress into the switching fabric until the moment the frame egresses
via the destination port.
QoS capability is very important due to the diverse topologies that exist in today’s network scenarios. These can
include, for example, streams from two different ports that egress via single port, or a port-to-port connection that
holds hundreds of services. In each topology, a customized approach to handling QoS will provide the best results.
Figure 117 shows the basic flow of PTP 850’s QoS mechanism. Traffic ingresses (left to right) via the Ethernet or
radio interfaces, on the “ingress path.” Based on the services model, the system determines how to route the
traffic. Traffic is then directed to the most appropriate output queue via the “egress path.”
Figure 93 QoS Block Diagram
(Optional)
Egress
Port
Scheduler/
Shaper
Standard QoS/ H-QoS
Queue
Manager
Marker
(Optional)
Egress
Port
Scheduler/
Shaper
Standard QoS/ H-QoS
Queue
Manager
Marker
(Optional)
Egress
Port
Scheduler/
Shaper
Standard QoS/ H-QoS
Queue
Manager
Marker
CET/Pipe
Services
Rate Limit
(Policing)
Classifier
(Optional)
Ingress
Port
Rate Limit
(Policing)
Classifier
(Optional)
Ingress
Port
Rate Limit
(Policing)
Classifier
(Optional)
Ingress
Port
GE/Radio
GE/Radio
GE/Radio
GE/Radio
GE/Radio
GE/Radio
The ingress path consists of the following QoS building blocks:
• Ingress Classifier – A hierarchical mechanism that deals with ingress traffic on three different levels: interface,
service point, and service. The classifier determines the exact traffic stream and associates it with the
appropriate service. It also calculates an ingress frame CoS and Color. CoS and Color classification can be
performed on three levels, according to the user’s configuration.
• Ingress Rate Metering – A hierarchical mechanism that deals with ingress traffic on three different levels:
interface, service point, and service point CoS. The rate metering mechanism enables the system to measure
the incoming frame rate on different levels using a TrTCM standard MEF rate meter, and to determine
whether to modify the color calculated during the classification stage.
Note
Ingress rate meters can be configure per service point or per service point CoS, but not on both.