The new MBR and APR-AMBR enforcement logic is implemented as described in the following sections.
MBR Enforcement Logic
A new token replenishment interval for MBR enforcement is introduced that is configurable at the APN and Global Configuration
level. The APN level configuration takes precedence over the Global Configuration level.
The following example describes the change:
flow limit-for-bandwidth direction downlink peak-data-rate 4000000 peak-burst-size 500000 violate-action discard
The Peak-Data-Rate (MBR) is set at 4 Mbps (4000000/8 = 500 KBps) and Peak-Burst-Size is 500 KBps (500000).
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Token Replenishment Interval is 1 msec:
MBR of 4 Mbps means 4000000/1000 = 4000/8 = 500 bytes token is accumulated and allowed every 1 msec. Therefore, 1 packet is
passed every 3 ms. Initial burst is 500 KBs (assumption is that each packet size is 1500 bytes).
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Token Replenishment Interval is 10 msec:
MBR of 4 Mbps means 4000000/100 = 40000/8 = 5000 bytes token is accumulated and allowed every 10 msecs. Therefore, 3 packets
are passed during a 10 ms interval. Initial burst is 500 KBs (assumption is that each packet size is 1500 bytes),
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Token Replenishment Interval is 100 msec:
MBR of 4 Mbps means 4000000/10 = 400000/8 = 50000 bytes token is accumulated and allowed every 100 msecs. Therefore, 33 packets
are passed during a 100 ms interval. Initial burst is 500 KBs (assumption is that each packet size is 1500 bytes).
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Token Replenishment Interval is 500 msec:
MBR of 4 Mbps means 4000000/2 = 2000000/8 = 250000 bytes token is accumulated and allowed every 500 msecs. Therefore, 166
packets are passed during a 500 msec interval. Initial burst is 500 KBs (assumption is that each packet size is 1500 bytes).
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Token Replenishment Interval is 1000 msec (1sec):
MBR of 4 Mbps means 4000000/1 = 4000000/8 = 500000 bytes token is accumulated and allowed every 1000 msecs. Therefore, 333
packets are passed during a 1 sec interval. Initial burst is 500 KBs (assumption is that each packet size is 1500 bytes).
APN-AMBR Enforcement Logic
A new token replenishment interval for MBR enforcement is introduced that is configurable at the APN Configuration level.
For more details, see the “Configuring APN-AMBR Enforcement (APN level)” section.
Recommendations
The following is recommended while configuring the token replenishment interval for MBR and APN-AMBR enforcement.
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To achieve data rate, not more than peak-data-rate at any point of time, it is recommended to configure peak-burst-size equals
to peak-data-rate (MBR) in bytes.
Examples:
For flow level bandwidth limiting:
flow limit-for-bandwidth direction downlink peak-data-rate 4000000 peak-burst-size 500000 violate-action discard
For dynamic rule bandwidth limiting:
policy-control burst-size auto-readjust duration 1
 Note |
Currently, default value of burst-size for dynamic rule bandwidth limiting is 5 times the MBR value.
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If violate-action is configured as lower-ip-precedence, new MBR enforcement algorithm based on token replenishment interval,
forwards packets, with zero ToS marked, if rate is beyond the configured MBR value. This may not improve efficiency of RAN
side scheduler. Therefore, it is recommended to use violate-action as discard.
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The burst size for APN-AMBR should be configured as [ambr (bps) / 8] bytes or if auto-readjust is used, duration should be
1 sec.
Examples:
AMBR downlink received from PCRF is 4000000 (4 Mbps)
apn-ambr rate-limit direction downlink burst-size 500000 violate-action drop
or
apn-ambr rate-limit direction downlink burst-size auto-readjust duration 1 violate-action drop
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For APN-AMBR enforcement, it is recommended to use violate-action as drop.
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For APN-AMBR violate-action shape, it is recommended to configure token replenishment interval as either 100 ms or 10 ms.
No other token replenishment intervals are not supported for APN-AMBR shaping.