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Cisco Bug: CSCur63846 - [15.0] SPGW Paging Success Rate changes between 14,15,15-ER

Last Modified

Dec 25, 2016

Products (1)

  • Cisco ASR 5000 Series

Known Affected Releases

15.0

Description (partial)

Symptom:
Between May and July of 2014, Customer upgraded the SPGWs in their network to 15.0 MR3-ER2 (build 54944).
Following these upgrades, we noticed a sharp improvement of the SGW paging success rate via ASR bulkstats.
We reached out to our local Cisco support at that time, who could not find that any change to the bulkstats formula to explain the change.

In the end, no explanation was ever achieved, but as the statistic showed improvement rather than degradation, Customer chose not to pursue the issue further.

Starting in September 2014, Customer began rolling out 15.0 MR3-ER4 (build 56352) to correct a 49-day counter wraparound issue (Cisco CDETS CSCuo23393/CSCun87338).
Following this upgrade, which was explicitly a PATCH load to the 54944 build, and should have involved no other corrections over what we previously had, we observed, after each individual upgrade over the course of several weeks, that the SGW paging success statistics were reverted to the success rate prior to the 15.0 upgrade in May/June/July; that is, they reflected the success rate previously seen on 14.0.

What's more, this single KPI is the only one affected between all three loads, so we feel this is too much to be a coincidence.

It's clear that something has changed, but Customer doesn't know if it reflects a real change in SGW behavior, or a simple change in how the bulkstat is being generated.
What is clear, it cannot reflect any changes on the network side, since a given SPGW upgrade within a pool, the SGW paging success rate will change for ONLY that node upgraded, and the other SPGW in the same pool, still on the older 15.0 load, will still show the same values.
If a network change were at work, then all nodes within a pool would be affected simultaneously, and this is not what is being observed.

Investigate and determine root cause of the SGW paging success rate change

Conditions:
Upgrade from 14.0 to 15.0
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