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Pixelated, Jittery, or Shuttering Video Streams due to Flow Control

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TitlePixelated, Jittery, or Shuttering Video Streams due to Flow Control
Symptoms
  • Pixelated, Jittery, or Shuttering Audio/Video Streams
  • Traffic Loss
Environment
  • EXOS
  • UDP Audio/Video Streams (Multicast/Unicast)
  • FlowControl TX Pause Enabled
Cause
If Flow Control TX Pause is enabled on ports in the network, these ports could be sending pause frames to upstream devices.  When a pause frame is received by a device supporting the reception of pause frames (rx-pause is enabled by default in EXOS), the device blocks all traffic on the port for a period of time.  This can have a very negative impact if received on an uplink or inter-switch connection.

The "show ports flow-control tx-pauses" and "show ports flow-control rx-pauses" commands (first available in EXOS 15.6.2) can help to identify if these frames are being sent and received in the network.
 
X460G2-24t-G4.2 # show port flow-control tx-pauses no-refresh 
Flow Control Frames Transmitted
Port     Pause    PFC0    PFC1    PFC2    PFC3    PFC4    PFC5    PFC6    PFC7
          Xmts    Xmts    Xmts    Xmts    Xmts    Xmts    Xmts    Xmts    Xmts
==============================================================================
1            -       -       -       -       -       -       -       -       -
2            -       -       -       -       -       -       -       -       -
3            -       -       -       -       -       -       -       -       -
4            -       -       -       -       -       -       -       -       -
5            -       -       -       -       -       -       -       -       -
6            -       -       -       -       -       -       -       -       -
7            -       -       -       -       -       -       -       -       -
8            -       -       -       -       -       -       -       -       -
9            -       -       -       -       -       -       -       -       -
10           -       -       -       -       -       -       -       -       -
11           -       -       -       -       -       -       -       -       -
12           -       -       -       -       -       -       -       -       -
13           -       -       -       -       -       -       -       -       -
14           -       -       -       -       -       -       -       -       -
15           -       -       -       -       -       -       -       -       -
16           -       -       -       -       -       -       -       -       -
17           -       -       -       -       -       -       -       -       -
18           -       -       -       -       -       -       -       -       -
19           -       -       -       -       -       -       -       -       -
20           -       -       -       -       -       -       -       -       -
21           -       -       -       -       -       -       -       -       -
22           -       -       -       -       -       -       -       -       -
23           -       -       -       -       -       -       -       -       -
24           -       -       -       -       -       -       -       -       -
25           -       -       -       -       -       -       -       -       -
26           -       -       -       -       -       -       -       -       -
27           -       -       -       -       -       -       -       -       -
28           -       -       -       -       -       -       -       -       -
29           -       -       -       -       -       -       -       -       -
30           -       -       -       -       -       -       -       -       -
31           -       -       -       -       -       -       -       -       -
32           -       -       -       -       -       -       -       -       -
33           -       -       -       -       -       -       -       -       -
34           -       -       -       -       -       -       -       -       -
===============================================================================
">" Name truncated, "-" tx-pause not enabled, "." Counter not available



 
Resolution
In most scenarios, flow control tx-pause should be disabled on inter-switch connections.  This should be disabled, or the reason for the generation of the flow control pause messages should be determined.  Flow Control TX Pause is disabled by default on all ports in EXOS.

To disable:
disable flow-control tx-pause ports <PORT>



 
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