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Configure MOS Score Monitoring

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Versa Operating SystemTM (VOSTM) devices can calculate a mean opinion score (MOS) to represent the user experience of audio, video, and voice applications. The MOS score is a measure of the quality of voice data traffic. When the traffic quality falls below the defined MOS score value, an alarm is logged. You define acceptable MOS scores when you configure an SLA profile for an SD-WAN traffic-steering policy.

You can use the MOS score as an SLA parameter in a policy-based forwarding (PBF) policy that is used to select the best path on which to forward real-time traffic between two SD-WAN branches. The best path is the one with the highest-priority SLA-compliant path for the codec. To calculate the MOS score, the VOS application identifier (AppID) software intercepts real-time protocol (RTP) and real-time transport control protocol (RTCP) traffic and uses the information in these packets to determine a path's MOS score.

To enable Layer 2 or Layer 3 SD-WAN traffic steering that uses a MOS score, you do the following:

  • Configure an SLA profile that includes MOS as the SLA parameter. Then, you associate the SLA profile with an SD-WAN forwarding profile, and you associate the forwarding profile with an SD-WAN traffic-steering policy. For more information, see Configure SD-WAN Traffic Steering.
  • Enable real-time flow monitoring. You can use real-time monitoring (RTM) to monitor real-time audio, video, and voice flows for quality and user experience. For more information and for a list of the applications and codecs for which MOS score–based monitoring is supported, see Configure Real-Time Monitoring.

Note that MOS score monitoring for Layer 2 SD-WAN traffic-steering policy is available for Releases 21.2.1 and later.

You can also use the MOS score in an SD-WAN traffic-steering forwarding profile to re-evaluate an SLA-violated link.

MOS-Based Path Selection

To calculate the MOS for a codec over a path, a traffic stream must flow over the path. This means that MOS-based path selection is reactive and that the MOS value of a path for a codec cannot be known in advance.

If there is no traffic stream over a path, the path is considered SLA-compliant and is assigned a MOS value of 5. (A MOS value can be from 0 through 5, where the value 5 is assigned to the best traffic quality.) Any path with a MOS value greater than or equal to the configured threshold is also considered SLA-compliant.

The MOS value for the path and codec is recorded. New paths can be selected at intervals based on the value of the recompute interval. This is the traditional way in which PBF performs path selection for all other SLA thresholds.

When deciding whether to select a new path, the VOS software considers the MOS score of that path. It calculates the path MOS value using the simultaneous localization and mapping (SLAM) metrics collected over that path. If a priority bucket contains multiple SLA-compliant paths, the VOS software always selects a path with the highest path MOS. Otherwise, precedence is based on path priority, and the VOS software select an SLA-compliant path with the highest priority.

When a path for codec violates the configured SLA, the path remains in the SLA-violated state, and it is not considered for forwarding traffic for the codec. To have the path be considered once again for forwarding, you can configure a path reevaluation interval. Then, a path whose MOS value does not meet the threshold remains in SLA-violated state for the duration of the reevaluation interval. During this period, the MOS value of the path increments slowly so that at the end of the reevaluation interval, the MOS value of the path may be greater than or equal to the configured threshold. At this point, a path MOS (PMOS), if available for the codec, is calculated and compared against the timer-updated MOS. (The PMOS is the MOS value calculated using the SLA metrics of the path.) If the PMOS value is less than the timer-updated MOS value, the MOS value of the path is updated to the value of the PMOS. If the PMOS value is greater than the threshold, the path is once again considered for traffic forwarding. This scheme prevents switching the flow to a path that is not optimal. Note, however, that the MOS value for a codec on a path is not kept forever and is eventually deleted.

For voice data, VOS devices use the MOS score to select the best available path for each voice stream. To calculate the MOS score, a VOS device uses the actual traffic, intercepting the Real-Time Transport Protocol (RTP) and RTP Control Protocol (RTCP) packets in a voice stream. From the RTP packets, it extracts jitter, loss, and delay (latency) information. The RTCP packets contain sender and receiver reports that include statistics about the quality of the voice stream. The VOS device calculates the MOS score continuously for every voice flow. You configure how often to check the MOS score and the threshold of acceptable MOS scores that are used to make the path-selection decision. The frequency of checking the MOS score affects how fast a voice steam can switch to a different path when the SLA for its path is violated. The SLA for a path is considered violated if the calculated MOS score for a voice flow is less than the threshold. You also configure the time interval after which a VOS device re-evaluates paths whose SLAs are violated.

The following figure illustrates the MOS path-selection process. Here, MOS path selection is enabled on the Site 1 branch device for traffic that Site 1 forwards to Site 2. Site 1 intercepts RTP and RTCP packets and uses the information in them to calculate the MOS score for the voice stream. Based on the score, Site 1 selects the best available path.

MOS_Path.png

Configure MOS Score Monitoring

Note that if you configure a MOS score in a profile, you do not have to configure other SLA parameters in the profile, because MOS considers delay, loss, and jitter.

To configure MOS score monitoring:

  1. Enable MOS score monitoring:
    1. In Director view, select the Configuration tab in the top menu bar.
    2. Select Templates > Device Templates in the horizontal menu bar.
    3. Select an organization in the left menu bar.
    4. Select a template in the main pane. The view changes to Appliance view.
    5. Select the Configuration tab in the top menu bar.
    6. Select Others > Organization > Settings in the left menu bar. The main pane displays panes related to organization settings.

      settings_page.png
    7. Click theedit_icon.png Edit icon in the Real-Time Flow Quality pane. In the Edit Configuration popup window, enter information for the following fields.

      edit_configuration.png
       
      Field Description
      Monitoring Click to enable MOS monitoring. Monitoring information is sent to the active collector of the default LEF profile. For information about configure a default LEF profile, see Configure Log Export Functionality. For information about associating a LEF profile with the configuration for a feature or service, see Apply Log Export Functionality.
      Compute interval Enter how often to log the MOS score. The minimum value is 2 seconds.
    8. Click OK.
  2. Configure an SLA profile that includes a MOS threshold:
    1. In Appliance view, select the Configuration tab in the top menu bar.
    2. For an SLA profile for Layer 2 traffic steering, select Services > Layer 2 SD-WAN > SLA Profiles in the left menu bar. The main pane displays the SLA profiles that are already configured.

      sla_profiles.png
    3. For an SLA profile for Layer 3 traffic steering, select Services > SD-WAN > SLA Profiles in the left menu bar. The main pane displays the SLA profiles that are already configured.

      sdwan_sla_profiles_page.png
    4. Click the add_icon.png Add icon, or select an existing SLA profile. The Add (or Edit) SLA Profile popup window displays.

      add_sla_profile.png
    5. For a Layer 3 SLA profile, select the General tab.
    6. In the Name field, enter a name for the SLA profile.
    7. In the MOS score field, enter a value for the MOS score. This is a value from 0 through 5, where 5 represents the best traffic quality.
    8. Configure the other fields, as described in Configure SLA Profiles for SD-WAN Traffic Steering (for Layer 3 traffic-steering policy).
    9. Click OK.
  3. Associate the SLA profile that includes the MOS threshold with a forwarding profile:
    1. In Appliance view, select the Configuration tab in the top menu bar.
    2. For an SLA profile for Layer 2 traffic steering, select Services > Layer 3 SD-WAN > Forwarding Profiles in the left menu bar.
    3. For an SLA profile for Layer e traffic steering, select Services > SD-WAN > Forwarding Profiles in the left menu bar.
    4. Click theadd_icon.png Add icon, or select an existing forwarding profile as shown below. The Add (or Edit) Forwarding Profile popup window displays.

      add_forwarding_profile.png
    5. Select the General tab, and enter information for the following fields.
       
      Field Description
      SLA Profile Select the SLA profile.
      SLA Violation Action Select Forward.
      Evaluate Continuously Click to enable continuous evaluation.
      Enable Symmetric Forwarding Click to enable symmetric forwarding.
    6. Configure the other fields, as described in Configure SD-WAN Traffic Steering (for Layer 3 traffic-steering policy).
    7. Click OK.
  4. Associate the forwarding profile with a Layer 2 or Layer 3 SD-WAN policy rule that matches RTP and RTCP traffic:
    1. In Appliance view, select the Configuration tab in the top menu bar.
    2. For a Layer 2 SD-WAN policy, select Services > Layer 2 SD-WAN > Policies > Rules in the left menu bar.
    3. For a Layer 3 SD-WAN policy, select Services > SD-WAN > Policies > Rules in the left menu bar.
    4. Click the add_icon.png Add icon to add a rule. The Add Rules window displays.
    5. Select the Enforce tab.

      add_rules_page.png
    6. In the Forwarding Profile field, select the forwarding profile you configured in Step 3 (here, Default-FP).
    7. Configure other fields in the popup window, as required. For more information, see Configure SD-WAN Policy.
    8. Click OK.

Verify the MOS Score Monitoring Information

To verify MOS score monitoring information:

  1. In Director view:
  2. Select the Monitor tab in the top menu bar.
  3. Select the organization from the left navigation panel.
  4. Select the Devices tab.

    device_page.png
  5. Select a device in the main pane. The view changes to Appliance view.
  6. To view the Layer 2 MOS score information:
    1. In the Services tab, select SD-LAN.
      sdlan_page.png
    2. Select the MOS tab, and then select a branch or Controller from the drop-down list.
      mos_page.png
  7. To view the Layer 3 MOS score information:
    1. In the Services tab, select SD-WAN.
    2. Select the MOS tab, and then select a branch or Controller from the drop-down list.

Troubleshoot MOS-Based Path Selection

This section describes the commands available to debug issues related to MOS-based path selection.

Troubleshoot the AppID Module

To troubleshoot the VOS application identifier software, use the following VTY commands:

  • To display the AppID modeule information, issue the show appid engine info command. The highlighted text in the output below shows that the MOS monitoring is enabled for Tenant 1 and disabled for Tenant 2 
    vsm-vcsn0> show appid engine info

Tenant ID = 1
    IxEngine Bypassed                = FALSE
    Firewall mode                    = nextgen_firewall
    ALG Bypassed                     = FALSE
    ALG Enable Bitmap                = 000000fe
    FTP ALG bounce check enable      = TRUE
    Num of app-sp-options tbl entry  = 0
    VQmon monitoring enabled         = TRUE
    VQmon reporting interval         = 2
Tenant ID = 2
    IxEngine Bypassed                = FALSE
    Firewall mode                    = nextgen_firewall
    ALG Bypassed                     = FALSE
    ALG Enable Bitmap                = 000000fe
    FTP ALG bounce check enable      = TRUE
    Num of app-sp-options tbl entry  = 0
    VQmon monitoring enabled         = FALSE
    VQmon reporting interval         = 5
  • To display statistics related to MOS-based events, issue the show appid stats debug command. The output displays statistics such as memory statistics and the number of events per traffic direction that were sent to PBF. 
    vsm-vcsn0> show appid stats debug

VQmon debug Information...

VQmon Memory usage :
        vqmon_mallocs  (M)                    : 306 (64976 bytes)
        vqmon_reallocs (R)                    : 0 (0 bytes)
        vqmon_frees    (F)                    : 304
        vqmon_create_stream_events            : 10
        vqmon_destroy_stream_events           : 10
        vqmon_indicate-pkt-events-fwd         : 15754
        vqmon_indicate-pkt-events-rev         : 14343
        vqmon_indicate-rtcp-pkt-events-fwd    : 75
        vqmon_indicate-rtcp_pkt-events-rev    : 72
        vqmon_report-events-fwd               : 144
        vqmon_report-events-rev               : 142
  • To view the MOS information for each session, issue the show vsf session handle extensive session-name command. The following output displays information about an RTP session. The highlighted text shows the latest MOS score reported to the PBF software as compared to the current time, to give an indication of when the next update will be sent to the PBF software. The RTCP Peered field displays Y, indicating that the corresponding RTCP session is successfully peered with the RTP session. This information must not be present in the VSF session command output when the session closes. If it is present, check the Created At and Destroyed At fields to determine the times between which to check the logs for issues. 
    vsm-vcsn0> show vsf session handle extensive 0x2000004

  Service Module Specific Information:
        SDWAN Session Ext: 7fa6cb8068f0
        SDWAN Flow info:
                Rule: r1
                Onward Flow:
                FP 235, RT gen 75 (current 75), tx ifindex 1053
                Prio 2, Win ID: 0, current 754269
                Codec G.711 u-law/PLC, mos score 420 path mos 0
        PBF Flow (Reverse) info
                Rule: None
    APPID Information:
      Appid = base.ip.udp.rtp
      ParentSessPresent = Y  Offload status  = No
      ALGInfoPresent    = N  FileNodePresent = N

     VQMon Information:
      Reporting Interval: 2000 ms
      RTCP Flow: N
      Forward direction:
       Stream Handle: 7fa6b58bfe00
       Created at: 2018-01-09 13:41:09
       Destroyed at: 1969-12-31 16:00:00
       MOS: 1074
       Last reported: 752872   Curr clock: 754270
       RTCP Peered: Y
      Reverse direction:
       Stream Handle: 7fa6b58c0c00
       Created at: 2018-01-09 13:41:10
       Destroyed at: 1969-12-31 16:00:00
       MOS: 1074
       Last reported: 753243   Curr clock: 754270
       RTCP Peered: Y

The following output the displays typical values for the fields in an RTCP ;session, for when the RTCP Flow field (highlighted) displays Y.

vsm-vcsn0> show vsf session handle extensive 0x2000004

  Service Module Specific Information:
        SDWAN Session Ext: 7fa6cb8069d0
        SDWAN Flow info:
                Rule: r1
                Onward Flow:
                FP 265, RT gen 75 (current 75), tx ifindex 1053
                Prio 2, Win ID: 0, current 900745
        PBF Flow (Reverse) info
                Rule: None
    APPID Information:
      Appid = base.ip.udp.rtcp
      ParentSessPresent = Y  Offload status  = No
      ALGInfoPresent    = N  FileNodePresent = N

     VQMon Information:
      Reporting Interval: 2000 ms
      RTCP Flow: Y
      Forward direction:
       Created at: 1969-12-31 16:00:00
       Destroyed at: 1969-12-31 16:00:00
       MOS: 0
       Last reported: 0   Curr clock: 900745
       RTCP Peered: N
      Reverse direction:
       Created at: 1969-12-31 16:00:00
       Destroyed at: 1969-12-31 16:00:00
       MOS: 0
       Last reported: 0   Curr clock: 900745
       RTCP Peered: N

Troubleshoot the Policy-Based Forwarding Module

You can view the MOS database maintained globally across all forwarding profiles using CLI and VTY commands.

To view the MOS score that is in the database, Issue the show orgs organization-name sd-wan path mos-score CLI command. The following output shows that there are two flows in the path, b1-w1, h1-w1, that they have the same MOS value of 3.57, and that they use codecs G.711 A-law and G.711 u-law, respectively.

admin@tcp-sdwan-br1-cli> show orgs org-services Customer2 sd-wan path mos-score
REMOTE       LOCAL    REMOTE
BRANCH       CIRCUIT  CIRCUIT  CODEC            MOS
------------------------------------------------------
Branch2      b1-w1    h1-w1    G.711 A-law/PLC  3.57
             b1-w1    h1-w1    G.711 u-law/PLC  3.57
             b1-w2    h1-w2    -                0.00
             b1-w3    h1-w3    -                0.00
controller1  b1-w1    c1-w1    -                0.00
             b1-w2    c1-w2    -                0.00             
             b1-w3    c1-w3    -                0.00

To view the same MOS score details from the database, issue the show sd-wan mos database-name detail VTY command. For example:

vsm-vcsn0> show sd-wan mos branch-database detail
Tenant    Branch     Local AC     Remote AC    Codec                MOS     Source
------    ------     --------     ---------    -----                ---     ------
1         16         b1-w1        c1-w1
                     b1-w2        c1-w2
                     b1-w3        c1-w3
1         102        b1-w1        h1-w1        G.711 u-law/PLC      3.57    VQMon
                                               G.711 A-law/PLC      3.53    VQMon
                     b1-w2        h1-w2
                     b1-w3        h1-w3
2         16         b1-w1        c1-w1
                     b1-w2        c1-w2
                     b1-w3        c1-w3
2         102        b1-w1        h1-w1
                     b1-w2        h1-w2
                     b1-w3        h1-w3

The VTY output has an additional field, Source, that identifies the source of the MOS value for that flow. The value for this field can be:

  • VQMon—MOS value was last updated as the result of a MOS event from the AppID module.
  • Timer—MOS value was last updated by the timer logic in the PBF module.
  • PMOS—MOS value was last updated because of a path MOS calculation.

To display the MOS database maintained for each forwarding profile, issue the following command:

admin@tcp-sdwan-branch1-cli> show orgs org-services customer2 sd-wan policies p1 rules app-state codec
      REMOTE       FORWARDING  SLA      LOCAL    REMOTE
NAME  BRANCH       PROFILE     PROFILE  CIRCUIT  CIRCUIT  CODEC            PRIORITY      MOS
-----------------------------------------------------------------------------------------------
r1    Branch2      fp1         slap1    b1-w1    h1-w1    G.711 u-law/PLC  SLA Violated  3.19
                                        b1-w2    h1-w2                     2             0.00
                                        b1-w3    h1-w3    G.711 u-law/PLC  2             3.57
      controller1  fp1         slap1    b1-w1    c1-w1                     2             0.00
                                        b1-w2    c1-w2                     2             0.00
                                        b1-w3    c1-w3                     2             0.00

The output above shows the state of a system in which an RTP session was initially flowing through path b1-w1, h1-w1 before it violated the MOS SLA and moved to path b1-w3, h1-w3.

You can view the same information from the VTY. The output below shows that there are two sessions on the path (b1-w1-, h1-w1) with codecs G.711 u-law and G.711 A-law, respectively. For both these streams, the path is at its configured priority of 2, because the MOS value meets the configured threshold of 3.25.

vsm-vcsn0> show sd-wan mos forwarding-profile Customer2/fp1 102 path-state
argc: 3 arg0: Customer2/fp1 arg1: 102 arg2: path-state
Branch     Local AC     Remote AC    Codec                MOS    Flows
------     --------     ---------    -----                ---    -----
102        b1-w2        h1-w2
           b1-w1        h1-w1        G.711 u-law/PLC      3.57   2
                                     G.711 A-law/PLC      3.57
           b1-w3        h1-w3

vsm-vcsn0> show sd-wan mos forwarding-profile Customer2/fp1 102 codec-state
Branch: 102
    Codec: G.711 u-law/PLC
        Priority: 2
        VLs: 17
    Codec: G.711 A-law/PLC
        Priority: 2
        VLs: 17

The highlighted text in the following VTY output shows an SLA-violated path for that codec, and it shows that there are no current session flows:

vsm-vcsn0> show sd-wan mos forwarding-profile Customer2/fp1 102 path-state
argc: 3 arg0: Customer2/fp1 arg1: 102 arg2: path-state
Branch     Local AC     Remote AC    Codec                MOS    Flows
------     --------     ---------    -----                ---    -----
102        b1-w2        h1-w2
           b1-w1        h1-w1        G.711 u-law/PLC      2.81   0
           b1-w3        h1-w3        G.711 u-law/PLC      3.57   1

vsm-vcsn0> show sd-wan mos forwarding-profile Customer2/fp1 102 codec-state
argc: 3 arg0: Customer2/fp1 arg1: 102 arg2: codec-state
Branch: 102
    Codec: G.711 u-law/PLC
        Priority: 2
        VLs: 51
        Priority: 11
        VLs: 17

To view the codec table created while booting up, issue the show sd-wan codec database VTY command. For example:

vsm-vcsn0> show sd-wan codec database
Codec Name                   Id      VQMON Id
-----------                 ----     --------

MPEG Audio Layer 1          1         1001
MPEG Audio Layer 2          2         1002
MPEG Audio Layer 3          3         1003
MPEG-2 AAC                  4         1004
AC-3 Audio                  5         1005
MPEG-4 AAC                  6         1006
MPEG-4 LD-AAC               7         1007
MPEG-4 HE-AAC               8         1008
WMA Professional            9         1009
MPEG-4 HE-AACv2             10        100a

Supported Software Information

Releases 20.2 and later support all content described in this article, except:

  • Release 21.2.1 adds support for configuring MOS score monitoring for Layer 2 SD-WAN traffic-steering policy.