DDN Throttling for non-Release 10 Compliant MME
Use the following configuration to configure DDN throttling for a non-release 10 MME:
configure
context context_name
sgw-service service_name
ddn throttle arp-watermark arp_value [ rate-limit limit time-factor seconds throttle-factor percent increment-factor percent [ poll-interval seconds ] throttle-time-sec seconds [ throttle-time-min minutes ] [ throttle-time-hour hour ] stab-time-sec seconds [ stab-time-min minutes ] [ stab-time-hour hour ]
no ddn throttle
end
NOTES:
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rate-limit : DDN permitted per second.
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time-factor : Time period in seconds over which SGW makes throttling decision (valid range 1-300 seconds).
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arp-value : Valid ARP value between 1 and 15. All the packets which have ARP greater than the configured values are throttled as per the throttling factor.
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throttling-factor : Percentage of DDN to be dropped upon detecting DDN surge (valid range between 1-100).
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throttling-time-sec : Time period in seconds over which DDN is throttled at SGW (valid range between 0-59 seconds).
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throttling-time-min : Time period in minutes over which DDN is throttled at SGW (valid range between 0-59 minutes).
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throttling-time-hour : Time period in hours over which DDN is throttled at SGW (valid range between 0-310 hours).
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increment-factor : Percentage value by which throttling factor is incremented dynamically, if existing throttling factor is insufficient to curb the DDN surge.
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poll-interval : Time in seconds (optional argument, default value = 1 second, poll interval < time-factor)
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stab-time-sec/min/hours : Stabilization time factor, time period over which if DDN rate returns to normal, then throttling need not be applied over the entire throttling time period.
DDN throttling for non-Release-10 compliant MME makes use of existing Release-10 throttling implementation at SGW. By providing a configuration mechanism for SGW service, operator can still apply ddn throttling without needing any feedback from MME. Some salient points of this feature are described below:
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The CLI configuration is applied per MME/S4-SGSN. Throttling parameters are tracked independently per MME/S4-SGSN.
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On configuring this feature through CLI, demuxmgr polls each sessmgr for number of DDNs sent. By default, polling is done every second. This time interval can be changed by configuring the poll-interval time. Greater the poll interval time, lesser the number of internal messages within the chassis. However, it would take longer to detect a DDN surge.
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By configuring time-factor, operator can specify the time interval for S-GW to apply throttling, if needed. It allows for some surge of DDNs if the net DDN rate is within specified limit over time-factor time interval. For example, time-factor= 10 seconds, ddn rate = 1000, poll interval = 2 seconds. Demux would poll each sessmgr every 2 seconds. Acceptable DDN rate limit is 1000*10 = 10000 DDNs every 10 seconds. Say after 2 seconds, 4000 DDNs were sent, in that case S-GW wouldn’t apply throttling until rate limit of 10000 DDNs is crossed within time period of 10 seconds. This allows for intermittent bursts of DDNs.
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DDN rate limit is configured through CLI. For example, if DDN rate limit is 1000 and poll interval = 1 second, time-factor = 5 seconds, then acceptable rate limit is 5000 DDNs over 5 seconds. If the number of DDNs sent by S-GW is greater than 5000 after 5 seconds, demuxmgr would ask all sessmgrs to initiate throttling.
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Percentage of DDNs to be throttled is configured through throttling-factor.
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Operator can specify increment-factor to increment throttling factor if the existing throttling factor is insufficient to curb the DDN surge. For example, if throttling-factor = 10%, ddn-rate = 1000, increment-factor=10%. Once throttling is applied, S-GW drops ~10% DDNs. However, if DDN rate is still greater than 1000, S-GW would increase throttling-factor to 20%. If this is still not sufficient, it would be incremented to 30%. After incrementing throttling factor, if number of DDNs dropped are greater than expected, throttling-factor would then be decrement by increment-factor. For example, in this case, after increasing throttling factor to 30%, if DDNs sent is less than 1000 per second (taking time-factor and poll-interval into consideration), throttling factor would be decremented to 20. The cap for decrementing throttling-factor would be the configured value (10% in this case).
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Operator can configure the time duration for which throttling is applicable at S-GW. This could be a large value in order of days (for example: 10 days or 240 hours). The operator has an option to stop throttling if DDN rate is well under control by configuring stabilization time factor. In such a case, DDNs won’t be needlessly dropped. For example, throttling-time =10 days, stab-time = 8 hours. After S-GW starts DDN throttling, in a time span of 8 hours, DDNs sent + DDNs dropped < ddn-rate * 8 hours, throttling would be stopped.