TD 92685EN
28 June 2012 / Ver. A
Troubleshooting Guide
Ascom i62 VoWiFi Handset
49
6. Troubleshooting
13 Investigate whether load balancing or Call Admission Control (CAC) can be
Implemented to ensure that voice traffic has access to the RF. Use a protocol analyzer
to analyze RF traffic. Inspect the WLAN controller log for any errors or system
overloads.
14 In case RX is not set in UP6 (Voice AC), m
ake sure that both handset and system is
configured to utilize CAC. Before a client can send traffic of a certain priority type, it
must have requested to do so via the TSpec mechanism. For example when a handset
wants to use the voice AC it must first make a request for use of that AC via the
action frame type ADDTS. If the voice AC is controlled by TSpec, the system must
grant the handset access to the requested AC before it could be used. In case no
TSpec request is sent, all downlink traffic will be directed to BE. For additional
information, see section Figure 14. Traceroute Result on
page 39.
15 Perform an air trace to determine whether the ADDTS action fram
es are exchanged
successfully and that the system grants the handset access to the voice AC (Status
code: Admission accepted). For additional information, see Appendix A.
16 Does the handset display the message “Network busy” wh
en attempting to establish
a call?
Yes: There is no access to the m
edium, that is, the system is declining the clients
request to use the voice AC. Go to step 17.
No: Go t
o the section External Interference.
17 Check system utilization
If the system utilization is reaching the limit s
et for when a new call is allowed to be
established, then CAC/TSpec are functioning as they should by limiting the number of
calls accepted and thereby preventing the network from becoming congested
If the system utilization is low and the “Network busy” message is still displayed, this
i
ndicates that the thresholds for CAC/TSpec are incorrectly set.
External Interference
18 External interference may occur when VoWiFi devices are forced to share th
e RF
spectrum with other devices. Such devices often create interference for wireless LAN
users. Perform a site survey with a spectrum analyzer to identify sources of
interference.
Check RTP Traffic
19 Perform an air trace of a roam to determine whether or not RTP dat
a is both sent and
received by the handset. If RTP data isn't received by the handset investigate that
the LAN switch is routing the RTP to the AP correctly. For additional information, see
Appendix A.
Security
If Extensible Authentication Protocol
(EAP) security is used, check if the full EAP exchange is
performed during the roam with an air trace or log of the Radius server. Normally the key-
caching function in the WLAN system and handset prevent a full EAP exchange during roam.
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