Radware Alteon, Инструкция по применению

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Alteon Application Switch Operating System Application Guide
Bandwidth Management
770
Document ID: RDWR-ALOS-V2900_AG1302
Data Pacing for Traffic Shaping Contracts
The mechanism used to keep the individual traffic flows under control in a traffic shaping contract is
called data pacing. It is based on the concept of a real-time clock and theoretical departure times
(TDT). The actual calculation of the TDT is based initially on the configured soft limit rate. The soft
limit can be thought of as a target limit for the ISP's customer. As long as bandwidth is available and
the classification queue is not being filled at a rate greater than the soft limit, the TDT is met for
both incoming frames and outgoing frames, and no borrowing or bandwidth limitation is necessary.
If the classification queue exceeds the soft limit, a frame is queued for transmittal and the TDT is
increased by the size of the frame multiplied by the transmittal rate of the queue.
Figure 131 - Real-time Clocks and Theoretical Departure Times, page 770 illustrates how data may
be paced in a traffic shaping contract. Six arriving frames are processed differently depending on
rate of the queue. Queue 1 processes each packet evenly. Queue 2 processes per 1500 bytes and
inserts some delay as it processes the first three 500 byte frames and then the next three frames.
Queue 3 processes at 3000 bytes per second and has ample capacity to process egress frames at
the same rate as the ingress frames.
Figure 131: Real-time Clocks and Theoretical Departure Times
If the data is arriving more quickly than it can be transmitted at the soft limit, and sufficient
bandwidth is still available, the rate is adjusted upward based on the depth of the queue, until the
rate is fast enough to reduce the queue depth or the hard limit is reached. If the data cannot be
transmitted at the soft limit, then the rate is adjusted downward until the data can be transmitted or
the CIR is hit. If the CIR is overcommitted among all the contracts configured for Alteon, graceful
degradation reduces each CIR until the total bandwidth allocated fits within the total bandwidth
available.