The path between a client of Office Communications Server and
the PSTN includes the Mediation Server, the IP/PSTN gateway, and
the connection to the PSTN phone itself. For external users of the
Office Communicator or Live Meeting client, there is also the edge
server deployment in the perimeter network. If PC-to-phone calling
is part of a PSTN audio bridge conference, the PSTN bridge can also
part of the communication path. Any point in the path can be
affected by connectivity or configuration issues that can cause
voice quality to degrade. The following table describes
PSTN-related voice quality issues.
Table 3. PSTN-related voice
quality issues
| Issue |
Potential Symptoms and Causes |
|
Uncontrolled network hops between the Mediation Server and the
IP/PSTN gateway
|
- Latency can increase because of the extra distances in this
call leg.
- Losses of RTP packets between the Office Communications Server
2007 Mediation Server and the IP/PSTN gateway may not be
recoverable because the gateways have limited processing power and
jitter buffer memory.
|
|
Incorrect codec settings on the IP/PSTN gateway
|
- G.711a-law and G.711mu-law are similar enough that sound may be
audible, but distortion can be extremely high.
|
|
Outdated IP/PSTN gateway firmware
|
- Office Communications Server requires compliance with newer
RTP/RTCP, such as support for contributing source CSRC fields in
the header. Incorrect parsing by the IP/PSTN gateway can lead to
audio artifacts (that is, extraneous noises, such as pops and
clicks) or audio loss.
|
|
IP/PSTN gateway bugs
|
- A gateway that is experiencing a significant load can cause
one-way audio issues (that is, on either the transmission being
sent or the transmission being received).
|
|
Incorrect IP/PSTN gateway routing
|
- Errors in routing configuration can cause the audio stream to
loop multiple times, which can cause loss of volume.
|
|
Other IP/PSTN configuration issues
|
- Configuration errors of any IP or PSTN component can cause
audio issues, including high or low volume, latency, line echo, and
call setup delays.
|
|
IPSec
|
- Enabling IPSec between the IP/PSTN gateway and the Mediation
Server can cause call setup delays or timeouts.
|
|
Dual-tone multi frequency (DTMF) detection
|
- The Mediation Server relies on the IP/PSTN gateway, which
controls tone detection, to translate dual-tone multifrequency
(DTMF) audio tones to RTP packets with encoded DTMF information.
|
|
Defective telephone
|
- A defective telephone can cause audio distortion, volume
issues, buzzing noises from interference, and other audio artifacts
(for example, popping and clicking).
|
|
Mobile phones
|
- Voice quality issues with mobile phone networks can introduce
issues that are not related to Office Communications Server.
|
|
PSTN audio conference bridges
|
- Latency and echo can occur in a conference, particularly if the
conference is connected to VoIP or mobile phone endpoints.
|
See Also
See Also