TD 92685EN
28 June 2012 / Ver. A
Troubleshooting Guide
Ascom i62 VoWiFi Handset
47
6. Troubleshooting
Voice Activity Detection
Voice Activity Detection (VAD) detects if the spe
aker is silent. To save bandwidth, the
transmitting device refrains from transmitting RTP packets for the duration of the silent
period. However, total silence can also lead to problems such as a perception by the parties
that the call has been dropped, sudden jarring changes in noise levels as the conversation is
resumed, and a general choppiness to the overall conversation.
To ameliorate these effects, a synthetic backgroun
d or so called comfort noise may be used
to fill the silent periods and make them sound more natural.
When troubleshooting one way or no audio problems, check if one of the parties is using
VAD and comfort noise. If, for example, the other end is not being heard, then turn off VAD
at that end to see if that resolves the issue.
6.1.4 Name Pres
entation Problems
Names are presented in a header in SIP messages
, for example "Charlie"
<sip:Charlie@10.11.24.244>.
Name updates are an issue with transfers or call diversio
ns. The kinds of problems that arise
when names are missing from SIP headers are:
• The intended recipient of a call has moved t
emporarily or permanently but cannot be
reached by the calling party
• The called party details are not displayed in the call
ing party’s handset.
There are three methods of naming used by handsets that are used in
the following order of
priority:
1 P-Preferred-Identity/P-Asserted-Identity: A c
all from a handset uses P-Preferred-
Identity and then the PBX changes it to P-Asserted-Identity. It might also add a name
to the P-Asserted-Identity. For example, the user may also suggest a name in the
form "NAME"<SIP URI>.
2 Remote party ID (Cisco compatible na
ming).
3 From field. A SIP header From field is used, that is,
the "NNNN" part of the from field
where the field contains " NNNN" <SIP URI>.
Of importance to the support engineer is the c
ontent of these headers when they reach the
calling or called parties. The header information is sent in the 18x provisional messages and
200 OK messages.
6.2 WLAN Troubleshooting Scenarios
This section illustrates, through examples, the kinds of performance issues that may arise
when operating a handset in a WLAN. Because the characteristics of sites using VoWiFi and
the issues experienced by users are likely to be very different, it would be difficult to provide
a single definitive method for resolving issues. Instead, the information in this section
suggests an approach to investigating and solving common WLAN issues.
6.2.1 Voice Problems while Roaming
User experience voice problems, both poor voice qu
ality or audio gaps while moving through
the site.
Software
Check that the WLAN and handset have compatible so
ftware versions and are configured
properly:
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