ECS3510-26P_Management Guide R02

C HAPTER 9 | Congestion Control
Rate Limiting
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For example, a Gigabit port has a 10 ms window size, so there are 100
scales per second, each scale having a bandwidth of 10 Mbps, and
using an inter-packet gap of 20 bytes.
Therefore, when the rate limit is set at 64 kbit/s, each scale has a
shared bandwidth of 80 bytes.
When the packet size = 64 bytes, and the gap = 20 bytes,
each packet = 84 bytes > 80bytes. Only one packet can pass through
in each scale. One second has 100 scales, so the rate is 100 packets
per second.
When the packet size = 640 bytes, and the gap = 20 bytes,
each packet = 660 bytes > 80 bytes. The switch will only let one packet
pass in each scale, so there are still 100 packets per second.
When the packet size = 1500 bytes, and the gap = 20 bytes,
each packet = 1520 bytes > 80 bytes. The switch will only let one
packet pass in each scale, so there are still 100 packets per second.
The following table shows the actual number of packets received when
various ingress rate limits are applied to packets of different sizes. The
values shown below were measured for both ingress rate limiting and
storm control functions.
Table 13: Effective Rate Limit
Packet Size Rate Limit Packets Received
64 bytes 64 kbit/s 100
128 kbit/s 200
256 kbit/s 400
512 kbit/s 800
1024 kbit/s 1600
2048 kbit/s 3105
128 bytes 64 kbit/s 100
128 kbit/s 100
256 kbit/s 300
512 kbit/s 500
1024 kbit/s 900
2048 kbit/s 1800
512 bytes 64 kbit/s 100
128 kbit/s 100
256 kbit/s 100
512 kbit/s 200
1024 kbit/s 300
2048 kbit/s 500