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Black screen when play back video record on IVS client

Publication Date:  2013-07-30 Views:  90 Downloads:  0
Issue Description
When playing back the video recording on IVS client, there is obvious half black screen, as below.
Alarm Information
None
Handling Process
Step 1: Capture the play back video steam on IVS client by wireshark tool. The analysis result shows that the packet loss rate is 13%. So, we can confirm now the root cause is packet loss and the next step is to find out where they’re lost.

Step 2: Connect the laptop directly to the S5328 and play back the video record. The video appears normal. So, we can make two conclusions: 1. the original video record in the storage is normal. 2. Packet loss happens between S5328 and the IVS client.
Step 3: Query the counter information on switches, like TOTAL ERROR, CRC. All such counter values are 0 and the port negotiation status is also normal, by which we can exclude the possibility of network cable or port failure.
Step 4: Using port mirror function to capture the S5328 output and S2328 input packets to analysis the packets loss rate. Both the packets loss rate are 0, which can prove that the packets are lost inside S2328.
Step 5: Re-analysis the packets captured in step 1. We find that the peak rate for I frame reaches 100 Mega-bit. Considering the input bandwidth is Giga-bit and the output bandwidth is 100 Mega-bit, we can confirm now the root cause is that the 100 Mega output port can’t process the instantaneous peak stream and the switch doesn’t have enough buffer to store the escaped packets.

There are two solutions:
1. Connect the IVS client to the Giga-bit port of the switch to evade the high-to-low stream model, which can prevent the packet escape.
2. Adjust the buffer mode of the switch: use the “burst-mode enable” command to enable the burst mode of the shared buffers, in which mode the switch will dynamically use all the buffer resource to the most emergent port rather than the default mode of sharing the buffer resource to all the ports evenly.
Screenshot after the problem solved:
Root Cause
Networking description:

IVS client is connected to an S2328 access switch and the port band width is 100Mega. S2328 and S5328 are connected by optical fiber. The media server is linked to S5328 directly with Giga bit port.
Usually, if the video appears as freezing, garbled or black screen, it’s always accompanied with packets loss in the network. So, we should start from checking packet loss on handling the problem, as below.
Suggestions
1. Due to the burst stream character of the IVS system, we must try to make sure the video stream can be transmitted with consistent bandwidth on all network components to prevent the packet loss caused by high-to-low stream model.
2. Some packets may be lost due to that the port doesn’t have enough buffer to store the escaped packets, in which case we can try to solve it by adjusting the buffer mode of the switch. However, different switch has different command for such function and we can refer to the product documents for that.

END