GL Communications Inc.
Telecom Test Solutions >  Case Study  >  Voice Quality

Call Quality Testing in the Contact Centres

Network diagram for call quality monitoring in call center


Audio quality is extremely important to large contact centers, irrespective of their infrastructure which can be TDM-based or VoIP based. Most contact centers have a hybrid TDM-VoIP infrastructure or are migrating towards All-IP transmission technology. A call center traffic includes receiving or transmitting a large volume of requests. An inbound call center administers incoming product support or information enquiries from customers. Outbound call centers are operated for telemarketing, market research or similarly other services. One of the challenges in receiving or transmitting a large volume of requests over integrated TDM and VoIP networks is to ensure service assurance and voice quality testing.

GL's QoS Test Suite provides different test tools to perform call quality monitoring and audio quality testing across a wide variety of networks (VoIP, TDM, PSTN, and Wireless).

GL’s VQuad™ Probe HD is one such test equipment that supports intrusive method to perform call quality assessment. The entire procedure of placing and receiving calls between end points is automated; quality is measured and reported centrally for verification. Thus, the test suite is ideally simulating conversations between customers and contact center executive, using ITU-standard male and female audio files combining with wide band (WB) and narrow band (NB) codec options (for HD and SD Audio). 

Once a test is scripted as per customer requirements, it can be reused for repeated future tests. The QoS test suite includes Voice Quality Testing software for measuring voice quality metrics per POLQA, PESQ, and MOS scores. The software also reports SNR, Jitter, Echo, and Delay measurements.
Besides intrusive test method, GL also offers other test tools such as Call Capture and Analysis for non-intrusive methods of signaling and audio quality assessment across a wide variety of networks (VoIP, TDM, PSTN, and Wireless).

Case Study

case study call quality monitoring in contact centers

As depicted in the test setup diagram above, GL’s VQuad™ Probe HD, and VQT test suite was recently deployed for a large contact center with multiple data centers at remote locations supported by T3 network infrastructure.

The FXO ports on GL's VQuad™ Probe HD were connected to two analog lines, commissioned by the contact center for testing purposes; FXO Port 1 is used for placing calls while FXO Port 2 is used for receiving the redirected call from the contact center, and recording the incoming call to perform measurements. In other words, once the call is generated from VQuad™, the contact center redirects the call back to the VQuad™ where the VQuad™ answers and begin the voice quality testing. This process continues for a multitude of calls cycling through all DS0s of the T3 T1 line of the call center (or multiple call centers).
During each established call the VQuad™ sends voice from one end, while recoding voice at the other end, and analyzes the recorded voice using the VQT POLQA algorithm.

Tests are performed using VQuad™ scripting for automation. Tests are repeated using both Male and Female ITU reference audio files to represent both low and high frequencies. Each call can be of any specified duration. The number of calls can also be specified within the script in order to test proper number of DS0s, and the script can be configured to call multiple Call Centers (either after first Call Center is complete, or round-robin multiple call centers). The VQuad™ scripting is extremely flexible for all scenarios.

The tests report a variety of measurements including VQT POLQA, RMS Power, Round Trip and/or One-Way Delay measurements, Signal/Noise Level measurements, and both Line Current and Line Voltage of the FXO analog ports.

All results/events/errors are available on the WebViewer™ (Central Database) with outputs going to PDF, Excel or CSV formatted files for combining with their own results. The results can be filtered and queried with Custom Reports generated (user-specified results/events). The Custom Reports can also be generated automatically using the WebViewer™ Scheduler with automated emails generated.


  • Scalable solution for unlimited number of FXO ports
  • Supported connectivity on Dual UTA HD – 2-Wire FXO, 4-Wire Balanced I/O, HSET Interfaces
  • Automated QoS Testing of Analog Network
  • Manual or Automatic operation of traffic generation and full call control
  • Wide Band (WB) and Narrow Band (NB) support (for HD and SD Audio)
  • Multiple Users and Tests per system
  • Run tests between systems
  • Fully automated and remote accessible via CLI
  • Remote accessible via Central Database
  • Full FXO Functionality and Analysis via flexible Scripts
  • Feature testing including Caller ID, 3-way call (conference call), call transfer, call forwarding, call waiting with Call ID
  • Send/Detect DTMF and user-specified single/dual-frequency tones
  • Both Tone and Pulse dialing supported
  • Fax testing supporting up to V34
  • Customized consolidated results along with the graphical report using WebViewer (web-based application)
  • Google Maps using the GPS co-ordinates saved in the database


Automated QoS Testing

  • Solution for testing analog 2-wire interfaces (PSTN, ATA, Media Gateway) and WB 4-wire Analog (Balanced headset, PTT, Mobile Phones)
  • Wide Band (WB) and Narrow Band (NB) support (for HD and SD Audio)
  • Automatic call control over several networks and supports transmit/capture of voice files in real-time from the various nodes.
  • Complete automation with enhanced scripting and remote operation including traffic generation, call control, and automated scheduling of operations

Remote Access to Events/Results

  • Current status of the entire test is displayed along with customized user statistics and results of the active tests
  • Real-time status of the entire network as well as remote accessibility of any node associated with the test network.
  • Remote monitoring with result query and real-time statistics
  • Identify different call types (Voice, SMS, Fax, Data test, Video …)
  • Customize criteria to drill down to required calls (3G, 4G, LTE, PSTN, VoIP call types)
  • Results, events, node status, and devices can be plotted on google map (GPS co-ordinates)
  • Customized report generation and report scheduling for the user specified filters

Voice Quality Analysis

  • Evaluate audio quality with MOS, E-Model, SNR, jitter, clipping, signal level, noise level, and delay measurements
  • Additional analytical metrics are also provided as a result of VQT Analysis (POLQA, PESQ test methods)
  • Analysis of uncompressed wav files consisting of narrow band, wide band and super wide band signals.
  • Measuring the effect of Packet Jitter in VoIP Network (requires GL PacketScan™)
  • Next generation voice quality testing (NB, WB, SWB)

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