> For the complete documentation index, see [llms.txt](https://docs.ceruleansonar.com/c/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.ceruleansonar.com/c/cerulean-ping-protocol/general-packet-definitions/set_sync_channel_number.md).

# SET\_SYNC\_CHANNEL\_NUMBER

### ID: 170

When operating multiple sonars together, it is usually important for them to ping simultaneously so that they do not interfere with each other. This can be accomplished using this SET\_SYNC\_CHANNEL\_NUMBER command to assign a channel number and a number of channels. Channel number 0 is the "master," so one of the channels must be assigned number 0 and the others should be assigned sequentially 1, 2, 3 etc. 

The devices synchronize their pinging via UDP messages. The master device sends a UDP broadcast message on port 51201, so all the devices must be on the same subnet. The "slave" devices acknowledge their readiness with a UDP message back to the specific master. This usually achieves synchronization within less than 100 uSec.

{% hint style="info" %}
NOTE: This functionality is currently only implemented on Omniscan, but the intention is to add support for other Ethernet capable sonars.
{% endhint %}

<table><thead><tr><th width="191">Data Type</th><th width="219">Name</th><th>Description</th></tr></thead><tbody><tr><td>u8</td><td>channel_number</td><td>channel number assigned to this device</td></tr><tr><td>u8</td><td>number_of_channels</td><td>number of sonars to be synchronized</td></tr></tbody></table>

Response is ACK. See [SYNC\_CHANNEL\_NUMBER](/c/cerulean-ping-protocol/general-packet-definitions/sync_channel_number.md) if you need to query a device for it's assigned sync channel number.&#x20;


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