ZyXEL Communications P-870HN-5xb User Manual page 215

The trTCM is based on the token bucket filter and has two token buckets
(Committed Burst Size (CBS) and Peak Burst Size (PBS)). Tokens are generated
and added into the two buckets at the CIR and PIR respectively.
All packets are evaluated against the PIR. If a packet exceeds the PIR it is marked
red. Otherwise it is evaluated against the CIR. If it exceeds the CIR then it is
marked yellow. Finally, if it is below the CIR then it is marked green.
The following shows how tokens work with incoming packets in trTCM:
• A packet arrives. If the number of tokens in the PBS bucket is less than the size
of the packet (in bytes), the packet is marked red and may be dropped
regardless of the CBS bucket. No tokens are removed if the packet is dropped.
• If the PBS bucket has enough tokens, the Device checks the CBS bucket. 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).
Otherwise, the packet is marked yellow.
P-870HN-5xb User's Guide
Chapter 16 Quality of Service (QoS)
215