performance analysis of a call center interface …system description • the call center monitoring...

Performance Analysis of a Call Center

Telecommunications InterfaceCS672 Spring 2004

Mohamed BenalayatRaymond Jordan

Overview• Call center monitoring and recording systems allow corporations to

monitor the performance of their agents by providing the ability to record and retrieve telephone conversations in real time.

• Monitoring systems usually require an interface between the Call Center Monitor/Recorder and the telecommunications infrastructure.

• The following paper is a study of the performance characteristics of such a call center telecommunications interface.

Project Goals• Determine the maximum workload that can be placed on the Call Center

Telecom Interface.

• Determine how to improve the Call Center Telecom Interface in order to achieve 100 or more simultaneous input lines.

System Description• The call center monitoring system under study can be described as

being composed of 2 functional components:

•A front-end telecommunications interface component, which functions as a call-processing unit. It is responsible for real time reception of digitized telephony data, processing the received data, converting to a recognized audio format, and forwarding to recording unit.

•A back end recording component which functions as a digital recording unit. It is responsible for recording and file management.

Call CenterPBX

Telecominterface 10BASE-T

interface

CPU/Disk

Recording unit

System DiagramCall Center Telecommunications Interface

CPU

Disk

NetworkOut to recording device

In from T-1 card

Hardware Description• Intel 1.263 GHz CPU

• 1 GB RAM

• Seagate Barracuda ATA IV 60 GB Hard Drive

• Average Write Service Time = 14.3 msec

• 10/100 Ethernet Card

• 24-channel telecom interface card(T1)

Workload Characterization• The system workload is a stream of digitized call conversations.

• Further monitoring of a production system, reviewing its logged data and discussions with the system architects, revealed the existence of 2 distinct traffic call classes.

• The first class, which we will call the PCM class, represents the call traffic digitized using the standard pulse code modulation techniques.

• The second class, which we will call VOIP class, represents the call traffic in the form of voice over IP calls. These calls may contain voice and data elements.

Data Collection Method• Our performance data collection process involved the use of a

telephone call simulation tool.

• The simulation tool is capable of streaming digitized audio files thru a T1 connection. Provided with a set of audio files, the tool will randomly pick a group of files to streamline.

• We had available to us a total of 12 audio files. 6 were PCM class and 6 were VOIP class.

• The Call Center Telecommunications Interface is equipped with a 24 channel T1 card. The audio simulator was configured to concurrently transmit 24 audio streams.

• Permon, the Microsoft windows performance tools was used to gather the performance statistics during the load testing.

• Ran 1-hour load test with only a PCM workload and another 1-hour load test with only a VOIP workload.

Queuing Network• The system can be represented by an Open Queuing Network. The

workload intensity is specified by the arrival rate of calls through the T1 interface.

• The number of calls simulated is limited only by the number of T1 interface cards installed in the unit.

ClusteringDisk Transfers vs. CPU Time

Disk Transfers/sec vs. %CPU Time

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ClusteringNetwork Bytes Sent vs. CPU Time

Network Bytes Sent/sec vs. %CPU Time

050,000

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PCM VOIP

System Completions

ClassNumber of

Lines

Average Session Length

Recordings Generated

(minutes)PCM 24 5.31 271VOIP 24 4.62 312

Basic Statistics for the PCM Service Workload

PCM% Processor

Time % Disk Time Disk Bytes/secNetwork Bytes

Sent/secU(cpu) U(disk) X(disk) X(net)

Mean 6.2 0.0 5,108.3 356,432.4Standard Deviation 2.7 0.1 8,641.0 27,385.6Sample Variance 7.5 0.0 74,666,318.7 749,970,852.6Coeff. Of Variance 0.4 1.6 1.7 0.1Minimum 0.0 0.0 2,355.2 0.0First Quartile (Q1) 4.3 0.0 3,481.6 347,264.7Median (Q2) 6.3 0.0 4,096.0 359,520.1Third Quartile (Q3) 8.1 0.0 4,480.0 375,268.4Maximum 14.3 0.6 110,863.5 376,915.5Range 14.3 0.6 108,508.3 376,915.5Largest 14.3 0.6 110,863.5 376,915.5Smallest 0.0 0.0 2,355.2 0.0Sum 1,489.6 7.5 1,225,990.2 85,543,779.9

Elapsed Time = 1 hour = 60 min. = 3600 secQ1

PCM Box and Whisker Plots

2,355.2 110,863.54,480.04,096.03,481.6

Disk Bytes/Sec

Q1 Q2 Q3

Q1

0.0 14.38.16.34.3

% Processor Time

Q2 Q3

0.0 376,915.5375,268.4359,520.1347,264.7

Network Bytes Sent/Sec

Q1 Q2 Q3

Basic Statistics for the VOIP Service Workload

VOIP% Processor

Time % Disk Time Disk Bytes/secNetwork Bytes

Sent/secU(cpu) U(disk) X(disk) X(net)

Mean 40.3 0.0 4,585.9 403,856.1Standard Deviation 7.9 0.1 3,113.5 30,635.0Sample Variance 62.7 0.0 9,693,663.1 938,501,610.0Coeff. Of Variance 0.2 2.0 0.7 0.1Minimum 3.1 0.0 2,455.0 182.7First Quartile (Q1) 35.1 0.0 3,583.9 398,367.6Median (Q2) 40.4 0.0 4,334.9 411,343.3Third Quartile (Q3) 45.2 0.0 4,889.6 411,796.1Maximum 58.5 0.8 44,762.1 447,753.4Range 55.4 0.7 42,307.0 447,570.8Largest 58.5 0.8 44,762.1 447,753.4Smallest 3.1 0.0 2,455.0 182.7Sum 9,676.4 11.1 1,100,614.4 96,925,454.6

Elapsed Time = 1 hour = 60 min. = 3600 sec

VOIP Box and Whisker Plots

2,455.0 44,762.14,889.64,334.93,583.9

Disk Bytes/Sec

Q1 Q2 Q3

Q1

3.1 58.514.3

45.28.1

40.435.1

% Processor Time

Q2 Q3

182.7 447,753.4

411,796.1411,343.3398,367.6

Network Bytes Sent/Sec

Q1 Q2 Q3

Service Demand CalculationsType Description Symbol PCM VOIP Units Formula Comment

Time Total Time T 3,600 3,600 sec Performance MonitorInput Lines 24 24 lines Test SimulatorCompleted Sessions System Arrivals/Completions A (Co) 271 312 sessions System Log

Average Time Per Session 318.82 276.92 secondsAverage Time Per Session 5.31 4.62 minutes

Throughput System Throughput Xo 0.075 0.087 sessions/sec = A / TCPU Utilization Ucpu 6.21% 40.32% % Performance Monitor

Busy Time Bcpu 223.44 1451.46 sec = Ui * TAverage Service Time Scpu 7.92E-10 7.92E-10 sec/transaction 1.263 Ghz processorService Completions Ccpu 282,199,242,017 1,833,195,030,583 transactions = Bi / SiThroughput Xcpu 78,388,678 509,220,842 transactions/sec = Ui / Si Utilization LawVisits to CPU Vcpu 1,041,325,616.3 5,875,625,098.0 = Ci / CoService Demand Dcpu 0.824 4.652 sec = Ui / Xo Service Demand Law

Disk Utilization Udisk 0.0311% 0.0462% % Performance MonitorBusy Time Bdisk 1.12 1.66 sec = Ui * TAverage Service Time Sdisk 0.014300000 0.014300000 sec/byte = Ui / Xi StorageReview.com Seagate Data SheetService Completions Cdisk 78.37 116.28 bytes = Bi / SiThroughput Xdisk 5,108.29 4,585.89 bytes/sec Performance MonitorVisits to Disk Vdisk 0.29 0.37 = Ci / CoService Demand Ddisk 0.004135392 0.005329316 sec = Ui / Xo

Network Interface Bytes Sent/sec 356,432.42 403,856.06 bytes/sec Performance MonitorTotal Bits/sec 2,851,459.33 3,230,848.49 Performance MonitorEthernet Speed 10,000,000.00 10,000,000.00 10 MbpsUtilization Unet 28.51% 32.31% % Performance MonitorBusy Time Bnet 1,026.53 1,163.11 sec = Ui * TAverage Service Time Snet 0.0000001 0.0000001 sec 10 Mbps Network InterfaceService Completions Cnet 10,265,253,583.4 11,631,054,555.7 bits = Bi / SiThroughput Xnet 2,851,459.3 3,230,848.5 bits/sec = Ui / SiVisits to Network Vnet 37,879,164.5 37,279,021.0 = Ci / CoService Demand Dnet 3.788 3.728 sec = Ui / Xo

Data AnalysisThread CPU Usage

• Notice that the CPU utilization for the PCM class is low compared to that of the VOIP class.

• The service demands show this trend.

•D(cpu, PCM) = 0.824 sec. D(cpu, VOIP) = 4.652 sec.

• The reason is the additional CPU requirements of the thread called to decode and extract data from VOIP data streams.

Thread Processor Usage

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Data AnalysisPCM Throughput and Resource Utilization vs. Number of Lines

PCM Resource Utilization & System Throughput vs. Number of Lines

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Data AnalysisPCM Resource Utilization vs. System Throughput

PCM Resouce Utilization vs. System Throughput

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Data AnalysisVOIP Throughput and Resource Utilization vs. Number of Lines

VOIP Resource Utilization & System Throughput vs. Number of Lines

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Data AnalysisVOIP Resource Utilization vs. System Throughput

VOIP Resouce Utilization vs. System Throughput

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Data AnalysisPCM Throughput Bounds

Throughput Performance Bound (PCM Inputs Only)

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NOTE: Scale of X-axis N is not linear.

Data AnalysisPCM Throughput Bounds (close-up)

Throughput Performance Bound (PCM Inputs Only)

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Data AnalysisThroughput Bounds

Throughput Performance Bound (VOIP Inputs Only)

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Data AnalysisVOIP Throughput Bounds (close-up)

Throughput Performance Bound (VOIP Inputs Only)

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Data Analysis PCM Response Time Bounds

Response Time Bound (PCM Inputs Only)

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Data AnalysisPCM Response Time Bounds (close-up)

Response Time Bound (PCM Inputs Only)

0.0002.0004.0006.0008.000

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Data Analysis VOIP Response Time Bounds


Response Time Bound (VOIP Inputs Only)

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Data AnalysisVOIP Response Time Bounds (close-up)

Response Time Bound (VOIP Inputs Only)

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Data AnalysisThroughput and Response Time vs. Number of Concurrent PCM Requests

Throughput and Response Time vs. Number of Concurrent PCM Requests

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Data AnalysisThroughput and Response Time vs. Number of Concurrent VOIP Requests

Throughput and Response Time vs. Number of Concurrent VOIP Requests

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Conclusions• PCM and VOIP classes are similar in their service demands for disk and

network usage. However, VOIP has a much higher CPU service demand that PCM.

• System throughput is limited by the network demands of both classes. Additionally, system throughput is limited by the CPU service demand of the VOIP class.

Open Queuing Network Solution

PCM Lines


System Completions

System Throughtput

Service Demand Utilizaton Busy Time Service Time

Resource Throughput

Queue Length Residence Time

Co Xo Di Ui Bi Si Xi Ni Ri'CPU 24 5.31 271.0 0.075 0.824 0.062 223.436 7.918E-10 78,388,678 0.116 1.542Disk 24 5.31 271.0 0.075 0.004 0.000 1.121 0.014 0.022 0.000 0.004Network 24 5.31 271.0 0.075 3.788 0.285 1,026.525 1.000E-07 2,851,459 0.728 9.669

Total Response Time 11.215

VOIP Lines


System Completions

System Throughtput


Resource Throughput


Co Xo Di Ui Bi Si Xi Ni Ri'CPU 24 4.62 312.0 0.087 4.652 0.403 1,451.461 7.918E-10 509,220,842 0.754 8.700Disk 24 4.62 312.0 0.087 0.005 0.000 1.663 0.014 0.032 0.000 0.005Network 24 4.62 312.0 0.087 3.728 0.323 1,163.105 1.000E-07 3,230,848 0.825 9.516


Total Lines


System Completions

System Throughtput

Average Service Demand Utilizaton Busy Time Service Time

Resource Throughput

Queue Length

Average Residence Time

Co Xo Di Ui Bi Si Xi Ni Ri'CPU 48 4.62 583.0 0.162 2.873 0.465 1,674.896 7.918E-10 587,609,520 0.870 5.372Disk 48 4.62 583.0 0.162 0.005 0.001 2.783 0.014 0.054 0.001 0.005Network 48 4.62 583.0 0.162 3.756 0.608 2,189.631 1.000E-07 6,082,308 1.553 9.587


Maximum WorkloadNumber of Lines for PCM and VOIP at 100% Resource Utilization

Number of Lines for PCM and VOIP at 100% Resource Utilization

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Number of Lines for PCM and VOIP vs. System Throughput at 100% Utilization

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Maximum WorkloadNumber of Lines for PCM and VOIP vs. Response Time

CPU Utilization approaching 100%

Network Utilization approaching 100%

Average Response Time at maximum workload is 1,194 seconds

Recommendations for Improvement

• Both classes will benefit from an upgrade network connection between the Call Center Telecom Interface and the Call Center Monitor/Recorder.

• Suggest 100 Mbps ethernet.

• Both classes will benefit from a faster CPU, but it is most important for the response time and throughput of the VOIP class. Today’s Intel Pentium 4 processors run at speeds over 3 GHz.

• Suggest 3 Ghz.

Improvement AnalysisImproved Service Demand Calculations

Type Description Symbol PCM VOIP Units Formula CommentTime Total Time T 3,600 3,600 sec Performance MonitorInput Lines 24 24 lines Test SimulatorCompleted Sessions System Arrivals/Completions A (Co) 271 312 sessions System Log

Average Time Per Session 318.82 276.92 secondsAverage Time Per Session 5.31 4.62 minutes

Throughput System Throughput Xo 0.075 0.087 sessions/sec = A / TCPU Utilization Ucpu 2.61% 16.97% % = Bi / 3600

Busy Time Bcpu 94.07 611.07 sec = Si * CiAverage Service Time Scpu 3.33E-10 3.33E-10 sec/transaction 3.00 Ghz processorService Completions Ccpu 282,199,242,017 1,833,195,030,583 transactionsThroughput Xcpu 78,388,678 509,220,842 transactions/sec = Ui / Si Utilization LawVisits to CPU Vcpu 1,041,325,616.3 5,875,625,098.0 = Ci / CoService Demand Dcpu 0.347 1.959 sec = Ui / Xo Service Demand Law

Disk Utilization Udisk 0.0311% 0.0462% % Performance MonitorBusy Time Bdisk 1.12 1.66 sec = Ui * TAverage Service Time Sdisk 0.014300000 0.014300000 sec/byte = Ui / Xi StorageReview.com Seagate Data SheetService Completions Cdisk 78.37 116.28 bytes = Bi / SiThroughput Xdisk 5,108.29 4,585.89 bytes/sec Performance MonitorVisits to Disk Vdisk 0.29 0.37 = Ci / CoService Demand Ddisk 0.004135392 0.005329316 sec = Ui / Xo

Network Interface Bytes Sent/sec 356,432.42 403,856.06 bytes/sec Performance MonitorTotal Bits/sec 2,851,459.33 3,230,848.49 Performance MonitorEthernet Speed 100,000,000.00 100,000,000.00 100 MbpsUtilization Unet 2.85% 3.23% % = Total Bits per sec / Ethernet SpeedBusy Time Bnet 102.65 116.31 sec = Ui * TAverage Service Time Snet 0.00000001 0.00000001 sec 100 Mbps Network InterfaceService Completions Cnet 10,265,253,583.4 11,631,054,555.7 bits = Bi / SiThroughput Xnet 2,851,459.3 3,230,848.5 bits/sec = Ui / SiVisits to Network Vnet 37,879,164.5 37,279,021.0 = Ci / CoService Demand Dnet 0.379 0.373 sec = Ui / Xo

Improvement AnalysisImproved Open Queuing Network Solution

PCM Lines


System Completions

System Throughtput


Resource Throughput


Co Xo Di Ui Bi Si Xi Ni Ri'CPU 24 5.31 271.0 0.075 0.347 0.026 94.066 3.333E-10 78,388,678 0.032 0.432Disk 24 5.31 271.0 0.075 0.004 0.000 1.121 0.014 0.022 0.000 0.004Network 24 5.31 271.0 0.075 0.379 0.029 102.653 1.000E-08 2,851,459 0.030 0.403


VOIP Lines


System Completions

System Throughtput


Resource Throughput




Total Lines


System Completions

System Throughtput

Average Service Demand Utilizaton Busy Time Service Time

Resource Throughput

Queue Length

Average Residence Time



Improvement AnalysisPCM Throughput and Resource Utilization vs. Number of Lines

PCM Resource Utilization & System Throughput vs. Number of Lines

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Improvement AnalysisPCM Resource Utilization vs. System Throughput

PCM Resouce Utilization vs. System Throughput

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Improvement AnalysisVOIP Throughput and Resource Utilization vs. Number of Lines

VOIP Resource Utilization & System Throughput vs. Number of Lines

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Improvement AnalysisVOIP Resource Utilization vs. System Throughput

VOIP Resouce Utilization vs. System Throughput

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Improvement AnalysisImproved Throughput and Response Time vs. Number of Concurrent PCM Requests

Throughput and Response Time vs. Number of Concurrent PCM Requests

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Improvement AnalysisImproved Throughput and Response Time vs. Number of Concurrent VOIP Requests

Throughput and Response Time vs. Number of Concurrent VOIP Requests

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Improvement AnalysisImproved Maximum Workload


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Improvement AnalysisNumber of Lines for PCM and VOIP vs. System Throughput

Number of Lines for PCM and VOIP vs. System Throughput at 100% Resource Utilization

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Number of Lines System Throughtput

Number of Lines for PCM and VOIP vs. Response Time at 100% Resource Utilization

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Number of Lines Average Response Time

Improvement AnalysisNumber of Lines for PCM and VOIP vs. Response Time

CPU Utilization approaching 100%

Average Response Time at maximum workload is 446 seconds

Outstanding Issues• The theoretical line capacity depends on adding additional 24 channel

T1 cards to the system. The overhead associated with each T1 card will slightly reduce the actual maximum line capacity.

• A good return on investment may not be possible when configuring the interface units at their maximum capacity. Investment costs need to be returned via software license fees, requiring the sale of a predetermined number of units.

• Response Time when configured at maximum line capacity is beyond acceptable limits. It is recommended to configure units at 50% of maximum capacity. The average response time when configure at 50% CPU utilization is 1.7 seconds.

Outstanding IssuesNumber of PCM vs. VOIP lines at 50% CPU Utilization


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performance analysis of a call center interface …system description • the call center monitoring...

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