UMTS Traffic CountersSlide title In CAPITALS 50 pt Slide subtitle 32 pt
Maurizio Molteni
Paolo Gattei
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TEI-05:002294 Uen Rev A
Outline
The aim of this document is to explain how to use the current traffic counters to calculate the resources allocation and the UMTS traffic (in Erlang)
Contents
Calculation of the average active RAB per cell
Calculation of the traffic in Erlang
Results verification
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These counters evaluate the traffic for every RAB in Kbit:
MAC and RLC headers are counted.
If there is no data to send, the counters are not incremented; that is, activity factor strongly impacts on the results.
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Why UL and DL is unbalanced for Speech service?
During the alerting phase the RAB is set up but the traffic is only DL for several seconds (even worse if there are song or similar trasmissions during this phase)
Authomatic answering machines (call center, phone box, services comunications..) only transmits in DL.
UL holes due to radio condition suspends the counting of the UL bit but not the ones in DL.
Other possible reasons:
The traffic on the DCCH could be different for UL and DL
Compressed Mode activation could have an impact.
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How could we corectly evaluate the average resources allocation?
The counters allows an estimate of the the RAB empoyment over a cell. The biggest unknown elements comes from the activity factor (AF).
pmUlTrafficVolumeCs12 x 1000
(12200 * 0.5 ) * ROP(sec)
RAB speech- all
Example of average RAB speech allocation in a ROP
For packet services the AF estimate is more difficult.
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These counters allow to monitor the number of active RAB:
One time each 30 seconds the number of all current active RABs (for each type) is summed in the counter pmSum****RabEstablish, and pmSamples****RabEstablish is stepped.
The ratio between sum and samples them defines the average numer of active RAB during the ROP.
The level of uncertainty here is not due to the AF but to the sampling (30 seconds is a long time).
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Note that this is still NOT in Erlang.
Hence, this can be used to evaluate the use of the resources but not the average number of users (or better services in use).
To have an Erlang value (as in GSM) we have to eliminate the contribution of the SHO.
NOTE: in P3 a new counter pmSumBestCs12Establish will be available, solving the problem with increments only for the best server cell in the AS.
pmSumCs12RabEstablish
pmSamplesCs12RabEstablish
For example, here we have the speech case:
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Use of the radiolink/radiolinkSet counters to evaluate the SHO contribution
pmSumUesWith i Rls j RlInActSet
pmSamplesUesWith i Rls j RlInActSet
For every cell the number of UEs with i Radio Link Sets e j Radio Links are is counted.
Hence the average number of the UEs with only 1 RL in the AS is:
pmSumUesWith1Rls1RlInActSet
pmSamplesUesWith1Rls1RlInActSet
The average number of the UEs with 2 RLs in the AS is:
pmSumUesWith1Rls2RlInActSet + pmSumUesWith2Rls2RlInActSet
pmSamplesUesWith1Rls1RlInActSet
Ue_2RL =
Ue_1RL =
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Active RAB Counters
The average number of the UEs with 3 RL in the AS is:
pmSumUesWith1Rls3RlInActSet + pmSumUesWith2Rls3RlInActSet +pmSumUesWith3Rls3RlInActSet
Ue_1RL + Ue_2RL + Ue_3RL
Ue_iRL
Perc_i_RL =
Ue_1RL + Ue_2RL + Ue_3RL
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Erlang calculation
1 RL
2 RL
2 RL
2 RL
2 RL
2 RL
2 RL
3 RL
3 RL
3 RL
3 RL
3 RL
3 RL
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...connectionswith 3 radio links
...connections with a single radio link ...
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The equivalent fraction of users belonging to a cell becomes:
PercUsersEq =
Finally the traffic in Erlang will be:
pmSumCs12RabEstablish
pmSamplesCs12RabEstablish
Erlang =
* PercUsersEq
This represents the fractions of user estimated to belong to a cell.
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Some results from a real network (P2.1.6)
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Some results from a real network (P2.1.6)
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Results Verification
Is it possible to evaluate the global traffic over the RNC using the following counters:
pmSumRabEstablish
pmSamplesRabEstablish
Average Numbers of users using a certain RAB in the whole RNC
(RNC Erlang)
(The calculation is applicable for each RAB type )
The result in this case is not affected by SHO contribution but it is available only for the whole RNC (not for the single cell)
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Object
PERIOD
RABSpeech
(sum/samples)
RABSpeech
(volumeUL)
2200-2300
161.39
146.74
109.79
108.84
In this case we checked the Erlang speech using both cell counters and RNC counters (not affected by SHO): you can see the good agreement between the sum of all cells and the global RNC counters (last two columns).
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