R3303-HP HSR6800 Routers ACL and QoS Configuration Guide

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is present. Even if congestion occurs in the network, Router B can still transmit packets at the rate of 32
kbps.
Figure 44 FRTS implementation
FRTS uses the parameters CIR ALLOW, CIR, CBS, and EBS for traffic shaping. FR PVCs can transmit
packets at the rate of CIR ALLOW. In case of bursty packets, FRTS allows an FR PVC to transmit packets
at a rate exceeding CIR ALLOW.
How FRTS works
FRTS is implemented using token buckets. The meanings of the related parameters in the protocol are
modified as required by the actual algorithm and principles. See Figure 45 f
or how a token bucket works.
Figure 45 How a token bucket works
In the token bucket approach, packets requiring traffic control are put into the token bucket for processing
before transmission. If enough tokens are available in the token bucket for sending these packets, the
packets are allowed to pass. If the number of tokens in the token bucket is not enough for sending these
packets, these packets are put into the FR class queue (the FRTS queue in FRTS implementation). Once
enough tokens are available in the token bucket, the packets are taken out of the FR class queue for
transmission. In this way, you can control the traffic of a certain class of packets. Tokens are in the unit
of bits.
The FR protocol-provisioned related parameters correspond to the FRTS parameters as follows:
• The sum of CBS and EBS equals the token bucket size.
• CIR ALLOW defines the number of tokens put into the token bucket per second.
For efficiency, the FRTS introduces the concept of dynamic Tc. Tc (Tc=size of packet/CIR ALLOW) allows
for dynamic adjustment depending on the transmitted packet size. The device allocates the required
tokens to the current packets waiting for transmission within the latest Tc regardless of the packet size
(which is smaller than 1500 bytes).
Take sending an 800-byte packet for example. Given the CIR ALLOW of 64000 kbps, it takes
Tc=6400/64000=0.1s (100ms) to put the required tokens into the token bucket. The packet is transmitted
successfully after 6400 bits of tokens are put into the token bucket within 100 ms.
Token bucket
Classification
Packets to be sent
through this interface
Packets sent
Tokens are put
into the bucket at
the set rate
FRTS queue
Tokens