ZyXEL Communications EMG3425-Q10A, User Manual

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Chapter 20 Bandwidth Management
EMG3425-Q10A User’s Guide
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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
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