ZyXEL Communications EMG3425-Q10A - Page 134

Chapter 20 Bandwidth Management
EMG3425-Q10A User’s Guide
134
similar types of traffic together and treating each type as a class. You can use CoS to give different
priorities to different packet types.
CoS technologies include IEEE 802.1p layer 2 tagging and DiffServ (Differentiated Services or DS).
IEEE 802.1p tagging makes use of three bits in the packet header, while DiffServ is a new protocol
and defines a new DS field, which replaces the eight-bit ToS (Type of Service) field in the IP header.
Tagging and Marking
In a QoS class, you can configure whether to add or change the DSCP (DiffServ Code Point) value,
IEEE 802.1p priority level and VLAN ID number in a matched packet. When the packet passes
through a compatible network, the networking device, such as a backbone switch, can provide
specific treatment or service based on the tag or marker.
Traffic Shaping
Bursty traffic may cause network congestion. Traffic shaping regulates packets to be transmitted
with a pre-configured data transmission rate using buffers (or queues). Your EMG3425-Q10A uses
the Token Bucket algorithm to allow a certain amount of large bursts while keeping a limit at the
average rate.
Traffic Policing
Traffic policing is the limiting of the input or output transmission rate of a class of traffic on the
basis of user-defined criteria. Traffic policing methods measure traffic flows against user-defined
criteria and identify it as either conforming, exceeding or violating the criteria.
The EMG3425-Q10A supports three incoming traffic metering algorithms: Token Bucket Filter
(TBF), Single Rate Two Color Maker (srTCM), and Two Rate Two Color Marker (trTCM). You can
Traffic
Time
Traffic Rate
Traffic
Time
Traffic Rate
(Before Traffic Shaping)
(After Traffic Shaping)
Traffic
Time
Traffic Rate
Traffic
Time
Traffic Rate
(Before Traffic Policing)
(After Traffic Policing)