ZyXEL P-794H User Guide - Page 175

Single Rate Three Color Marker

Page 175 highlights

Chapter 14 Quality of Service (QoS) • After a packet is transmitted, a number of tokens corresponding to the packet size is removed from the bucket. • If there are no tokens in the bucket, the P-794H stops transmitting until enough tokens are generated. • If not enough tokens are available, the P-794H treats the packet in either one of the following ways: In traffic shaping: • Holds it in the queue until enough tokens are available in the bucket. In traffic policing: • Drops it. • Transmits it but adds a DSCP mark. The P-794H may drop these marked packets if the network is overloaded. Configure the bucket size to be equal to or less than the amount of the bandwidth that the interface can support. It does not help if you set it to a bucket size over the interface's capability. The smaller the bucket size, the lower the data transmission rate and that may cause outgoing packets to be dropped. A larger transmission rate requires a big bucket size. For example, use a bucket size of 10 kbytes to get the transmission rate up to 10 Mbps. 14.7.4 Single Rate Three Color Marker The Single Rate Three Color Marker (srTCM, defined in RFC 2697) is a type of traffic policing that identifies packets by comparing them to one user-defined rate, the Committed Information Rate (CIR), and two burst sizes: the Committed Burst Size (CBS) and Excess Burst Size (EBS). The srTCM evaluates incoming packets and marks them with one of three colors which refer to packet loss priority levels. High packet loss priority level is referred to as red, medium is referred to as yellow and low is referred to as green. The srTCM is based on the token bucket filter and has two token buckets (CBS and EBS). Tokens are generated and added into the bucket at a constant rate, called Committed Information Rate (CIR). When the first bucket (CBS) is full, new tokens overflow into the second bucket (EBS). All packets are evaluated against the CBS. If a packet does not exceed the CBS it is marked green. Otherwise it is evaluated against the EBS. If it is below the EBS then it is marked yellow. If it exceeds the EBS then it is marked red. The following shows how tokens work with incoming packets in srTCM: • A packet arrives. The packet is marked green and can be transmitted if the number of tokens in the CBS bucket is equal to or greater than the size of the packet (in bytes). P-794H User's Guide 175

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Chapter 14 Quality of Service (QoS)
P-794H User’s Guide
175
After a packet is transmitted, a number of tokens corresponding to the packet
size is removed from the bucket.
If there are no tokens in the bucket, the P-794H stops transmitting until enough
tokens are generated.
If not enough tokens are available, the P-794H treats the packet in either one of
the following ways:
In traffic shaping:
• Holds it in the queue until enough tokens are available in the bucket.
In traffic policing:
• Drops it.
• Transmits it but adds a DSCP mark. The P-794H may drop these marked
packets if the network is overloaded.
Configure the bucket size to be equal to or less than the amount of the bandwidth
that the interface can support. It does not help if you set it to a bucket size over
the interface’s capability. The smaller the bucket size, the lower the data
transmission rate and that may cause outgoing packets to be dropped. A larger
transmission rate requires a big bucket size. For example, use a bucket size of 10
kbytes to get the transmission rate up to 10 Mbps.
14.7.4
Single Rate Three Color Marker
The Single Rate Three Color Marker (srTCM, defined in RFC 2697) is a type of
traffic policing that identifies packets by comparing them to one user-defined rate,
the Committed Information Rate (CIR), and two burst sizes: the Committed Burst
Size (CBS) and Excess Burst Size (EBS).
The srTCM evaluates incoming packets and marks them with one of three colors
which refer to packet loss priority levels. High packet loss priority level is referred
to as red, medium is referred to as yellow and low is referred to as green.
The srTCM is based on the token bucket filter and has two token buckets (CBS and
EBS). Tokens are generated and added into the bucket at a constant rate, called
Committed Information Rate (CIR). When the first bucket (CBS) is full, new
tokens overflow into the second bucket (EBS).
All packets are evaluated against the CBS. If a packet does not exceed the CBS it
is marked green. Otherwise it is evaluated against the EBS. If it is below the EBS
then it is marked yellow. If it exceeds the EBS then it is marked red.
The following shows how tokens work with incoming packets in srTCM:
A packet arrives. The packet is marked green and can be transmitted if the
number of tokens in the CBS bucket is equal to or greater than the size of the
packet (in bytes).