Investigating Possible Causes of Voice Quality Issues

Communications Server 2007 R2

Topic Last Modified: 2009-05-22

Typically, Enterprise Voice quality issues are reported by users. Investigations of voice quality issues almost always start from examining the user’s report. Interviews with the user are often required to gather additional information about the user’s experience. The following table describes the most common issues that are reported by users and the most likely cause of each issue: the device, the network, or the PSTN. You can use the following table to begin your investigation of the most likely source of the issue.

It is possible to identify and resolve some issues before they become user-reported issues. Routine monitoring and evaluation of events can facilitate early identification and resolution of potential issues. For details, see Heading off Potential Problems with Enterprise Voice.

Table 4.   Possible causes of voice quality issues

Issue Possible cause: Likelihood Explanation

Low volume

Device : High

PSTN: Medium

Network: None

Device: Volume setting is too low or person speaking is too far from microphone.

PSTN: Phone volume is too low, IP/PSTN gateway gain settings are too low.

Missing words in conversations

Network: High

Device: Medium

PSTN: None

Network: Packet loss or jitter.

Device: Microphone volume is too low, or person speaking is too far from microphone or speaking too softly.


Network: High

Device: Medium

PSTN: None

Network: Packet loss or jitter.

Device: Audio enhancement hardware or software is interfering with audio processing in Office Communications Server, microphone or speaker is defective, or volume setting is too high resulting in clipping.

One-way audio

Network or PSTN: Medium

Device: Medium

Network: Improper network routing or severe one-way loss.

PSTN: Defective or incorrectly configured gateway, or errors in codec configuration.

Device: Audio input or output is muted or volume is turned down to 0.

Long call setup time

Network, PSTN, or Device: Medium

Network: High latency, IPSec, or packet loss.

Device: Slow device initialization.

PSTN: Slow PSTN signaling.

Audio delays

Network: High

PSTN or Device: Medium

Network: High latency or traffic shaping.

PSTN: Long PSTN segment, calls involving mobile phones or PSTN audio conference bridges.

Device: Signal processing or buffering is slow.


Device: High

PSTN: Medium

Network: None

Device: Incompatible devices (for example, an omni-directional microphone that picks up sound from the speakers, resulting in feedback) or devices that come as a set but are not used together (for example, a microphone and speaker that are designed to work together, but are not used together), microphone not well isolated from speakers, multiple microphones in the same room.

PSTN: Limited or no echo cancellation on phone line or PSTN audio conference bridges.

Loud static or background noise

Device: High

Network or PSTN: None

Device: device drivers, incorrect placement of device, faulty ground or cabling.

After you have identified the likely source, see the appropriate troubleshooting topic for information about how to resolve the issue, as follows:

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