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Quality of Service Overview
Figure 5
Rate Shaping
Rate Shaping throttles the rate at which a port transmits (outbound) queued packets. Rate Shaping
buffers packets received above the configured rate on a per CoS basis, rather than dropping them.
Only when buffer capacity is exceeded are packets dropped. Rate shaping may be configured for a
CoS on a port, for an 802.1p priority on a port, or for all Classes of Service on a port.
Figure
with rate shaping applied.
Figure 6
Rate shaping retains excess packets in a queue and then schedules these packets for later
transmission over time. Therefore, the packet output rate is smoothed and bursts in transmission
are not propagated as seen with rate limiting.
Rate shaping can be implemented for multiple reasons, such as controlling bandwidth, to offer
differing levels of service, or to avoid traffic congestion on other links in the network by removing
the burstiness property of traffic that can lead to discarded packets. Rate shaping is important for
real‐time traffic, where packet loss is extremely detrimental to these applications. Instead of
February 22, 2008
Rate Limiting Clipping Behavior
6 illustrates how bursty traffic is smoothed out when it bursts above the assigned threshold
Rate Shaping Smoothing Behavior
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