Monitoring, Management & Location Tracking

How AOS calculate calculating quality parameters for a voice call from the corresponding RTP streams

The following quality parameters will be computed:

  1. Jitter
  2. Delay
  3. Packet Loss

 In a wireless network, a packet can be classified as upstream or downstream depending on whether it is transmitted to the AP or received from the AP.
 
By monitoring the incoming RTP stream on the AP, we will calculate upstream jitter and upstream packet loss. Similarly, by monitoring the downstream RTP packets in the AP’s queues we will calculate the downstream jitter and downstream packet loss. The downstream delay will be computed by measuring the delay between the transmission of the packet and the reception of the corresponding 802.11 ACK. Using all this information, we will calculate upstream and downstream rvalue of a call. 
 
To identify RTP packets on AP, the AP should either be in decrypt tunnel mode or split tunnel mode (remote AP). Downstream call quality will work only in decrypt tunnel mode and split tunnel mode.

 

At present, we get call quality information from the RTCP protocol. However, most voice phones do not support RTCP protocol. Also, currently, we only show average quality values which are not very useful. This limits our capability to troubleshoot voice-related issues.
 
A voice call or session has both signaling traffic and media traffic. When a user experiences quality issues during a call, they could be either due to signaling traffic or media traffic. Signaling issues are easy to debug because we generate enough signaling logs. However, it is very difficult to troubleshoot media issues. To troubleshoot media issues, we need periodic quality data for both upstream and downstream RTP traffic. This is where this feature comes in – it will generate periodicquality parameters from the RTP stream.

 

 

    Upstream Downstream
Encrypt tunnel   Data path will accumulate RTP header and send it to control path for processing. Control path will calculate jitter, packet loss and rvalue. AP cannot monitor traffic in encrypt tunnel. The only possible way to calculate downstream quality parameter and delay is by checking V tag in packet and monitoring them.
Decrypt tunnel   Data path will accumulate RTP header and send that to control path for processing. Control path will calculate jitter, packet loss and rvalue. AP will be able to deep inspect RTP packets. It will calculate jitter, packet loss and delay and sent the results to control path
  Clients on same AP RTP will get locally bridge and packets won’t hit controller's data path. ASAP firewall will accumulate RTP headers and send it to AP process. AP will then calculate jitter and packet loss and send the result to controller via VoIP lite AP will be able to deep inspect RTP packets. It will calculate jitter, packet loss and delay and sent the results to control path
Split tunnel Clients on different AP RTP packets will cross ASAP firewall and controller's data path. We will have to send a message to AP to stop analysis on AP. Controller will accumulate RTP header and send it to control path Same as above
Bridge   Not supported Not supported

 

The following quality metrics will be computed on the AP when RTP Analysis feature is enabled:

  • For downstream frames:
    • Transmission Delay: The transmission delay will be computed from the time the frame arrives on the AP till the time the hardware sends a notification to the driver that the frame was successfully received by the client
    • Jitter: The variance in transmission of successive frames
    • Packet Loss: The loss if any due to the instability of the wireless medium.
  • For upstream frames, it is not possible to determine the classical end-to-end delay. Rather, the upstream delay computed on the AP will be the sum of the time taken to process the frame on the AP and the time taken to send it to the controller.
    • The AP will compute:
      • Processing Delay: The processing delay will be computed from the time the frame is decrypted till the time it is enqueued onto the GRE tunnel.
      • Propagation Delay: This is the delay in propagating the frame from the AP to the controller datapath.

#show voice rtp-analysis
RTP analysis result table
-------------------------                                    
Id  Client(IP)   Client(MAC)        Direction   Jitter  Delay(ms)  Pkt loss(%)  rvalue
--  -----------  -----------------  ---------   ------  ---------  -----------  ------
01  10.16.66.21  11:22:33:44:55:66  Upstream    04.530  59         1.223        73
                                    Downstream  08.195  34         2.112        69
02  10.16.66.21  11:22:33:44:55:66  Upstream    15.122  165        0.111        82
                                    Downstream  16.934  97         5.092        61
03  10.16.66.21  11:22:33:44:55:66  Upstream    23.344  51         2.435        69
                                    Downstream  42.323  22         7.323        60
04  10.16.66.22  11:22:33:11:22:33  Upstream    04.331  105        1.343        79
                                    Downstream  08.246  25         0.323        84
05  10.16.66.22  11:22:33:11:22:33  Upstream    15.237  90         1.222        76
                                    Downstream  16.174  85         0.332        81  

show voice rtp-analysis id 1
Upstream RTP analysis for Client(MAC) 11:22:33:44:55:66
-------------------------------------------------------
Sample time      Jitter  Delay(ms)  Packet loss(%)  rvalue
---------------  ------  ---------  --------------  ------
Dec 16 01:02:55  01.000  45         1.222           78
Dec 16 01:02:50  03.102  68         1.424           78  
Dec 16 01:02:45  00.223  34         0.544           81
Dec 16 01:02:40  01.223  31         0.323           83
Dec 16 01:02:35  01.223  33         0.343           81
Dec 16 01:02:30  04.534  90         2.342           67
Dec 16 01:02:25  02.343  38         2.034           62 
Dec 16 01:02:20  07.324  04         2.343           60 
Dec 16 01:02:15  19.232  92         1.343           79
Dec 16 01:02:10  15.334  05         1.457           76
Dec 16 01:02:05  14.232  34         1.036           77
Dec 16 01:02:00  21.232  20         1.454           78
 
Downstream RTP analysis for Client(MAC) 11:22:33:44:55:66
---------------------------------------------------------
Sample time      Jitter  Delay(ms)  Packet loss(%)  rvalue
---------------  ------  ---------  --------------  ------
Dec 16 01:02:55  01.000  45         1.222           78
Dec 16 01:02:50  03.102  68         1.424           78  
Dec 16 01:02:45  00.223  34         0.544           81
Dec 16 01:02:40  01.223  31         0.323           83
Dec 16 01:02:35  01.223  33         0.343           81
Dec 16 01:02:30  04.534  90         2.342           67
Dec 16 01:02:25  02.343  38         2.034           62 
Dec 16 01:02:20  07.324  04         2.343           60 
Dec 16 01:02:15  19.232  92         1.343           79
Dec 16 01:02:10  15.334  05         1.457           76
Dec 16 01:02:05  14.232  34         1.036           77
Dec 16 01:02:00  21.232  20         1.454           78

 

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Last update:
‎11-04-2014 01:26 PM
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