ZEC supports failover based unrecovered packet errors. The trigger for the failover includes unrecovered packets. Through ZEN Master and through the ZEC API it is possible to combine multiple triggers into a Boolean expression to determine when to the trigger the failover.

In addition ZEC features hitless failover for inputs, enabling undisrupted streaming when switching from one source to another. The hitless failover configuration involves grouping two or more inputs in a "Failover Group". If the inputs are identical (i.e. two or more binary-identical streams with synchronized RTP headers), whenever one of them is disrupted or interrupted completely, ZEC will seamlessly use the packets of the other input without any disruptions by "merging" the streams. The merging of the streams can be achieved using one of the following methods:

RTP headers (SMPTE 2022-7) – if the sources are RTP and the RTP headers were maintained, ZEC will use the SMPTE 2022-7 to compare and merge the two streams in order to allow hitless failover. This option is the most recommended as it will use the sequence and the timestamp in the packets to compare which packets are missing. This method is more accurate than methods that compare the entire payload or methods that use sophisticated DNA sequencing algorithm, which are more error prone, as the payload may have multiple matches.
RTP headers or TS content – if the sources do not have RTP headers, ZEC will try to merge using the MPEG-TS content itself.

Note

If the streams are not identical, the failover process will not be seamless and may take up to a second.

The following procedure describes how to configure inputs as a Failover Group in ZEC.

To create a Failover Group:

On the Input screen of ZEC, select the checkboxes of the relevant identical input streams.
At the top of the inputs list, click the Marked drop-down menu and then click Failover Group.
The Create a Failover Group window opens:
In the Stream ID field, type a new name for Failover Group. This name will appear in the list of Inputs.
In the Max Outputs field, type the number of desired concurrent outputs that can use the Failover Group. Default: Unlimited.
In the Search Window field, type the time frame in which the system can search for the relevant packets in a matching stream. If there is a latency difference between the streams in the group, the Search Window value should be higher than the latency difference between the streams.
In the Max Bitrate field, specify the maximum bitrate of the stream. Default: 8000. This is used for internal memory allocation and will not affect the transmitted bitrate. Recommended: double the bitrate of the highest bitrate stream.
In the Merge mode field, select one of the following:
- No merge – select this option if you want Zixi to treat the streams as different and not try to merge the streams. In case the Merge Mode is set to No Merge, the Search Window time specifies how long the stream will wait for packets before attempting to switch between streams. In this case, the time period specified in the Search Window field defines how long the stream will wait for packets before attempting to switch between streams.
- RTP headers (SMPTE 2022-7) – select this option if the sources are RTP and the RTP headers were maintained. In this case, Zixi will use the SMPTE 2022-7 to compare and merge the two streams in order to allow hitless failover. This option is the most recommended as it will use the sequence and the timestamp in the packets to compare which packets are missing. This method is more accurate than methods that compare the entire payload or methods that use sophisticated DNA sequencing algorithm, which are more error prone, as the payload may have multiple matches.
- RTP headers or TS content – select this option if you are not sure if the sources do have RTP headers. In this case, Zixi will try to merge using RTP and if not, using the MPEG-TS content itself
In the Keep RTP headers checkbox, enabling this option enables using SMPTE 2022-2 FEC and 2022-7 hitless failover together. The failover group will use 2022-7 and will merge streams based on sequence in the RTP header, and not on content with DNA matching. When creating the Failover Group select the Keep RTP Headers again (in the failover group screen) to keep the RTP headers after the merge. If it is not selected, Zixi will merge based on the headers (using SMTE 2022-7), but then drop the headers thereafter.
Under Candidates, if you want to configure one or more of the streams as back up, select the checkbox next to the relevant stream. Backup streams will be used only when all the "Primary" streams are down.
Configure additional parameters as required.
Click OK.
The Failover Group is added to the list of inputs, listing the sub-streams that are part of the group. The system will automatically detect the offset between the sub-streams and display it in milliseconds under Offset (ms).

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