Mesh-NOW supports group-scoped messaging. Only nodes that belong to the group receive the message; everyone else ignores it for delivery purposes.

Setting a Group

// Join group 42
mesh_now_set_group(42);

// Switch to group 0 (default / no group)
mesh_now_set_group(0);

The group ID is a single byte (uint8_t), so there are 255 usable groups. Group 0 is the default and means “no group filter.”

Sending Group Messages

// Send to group 42
mesh_now_send_group(42, "Hello, group!");

// Any node with group_id == 42 will receive this

Receiving Group Messages

When a MSG_TYPE_GROUP message arrives, the library checks the local group ID:

else if (mesh_msg.type == MSG_TYPE_GROUP)
{
    if (local_group_id != 0 && mesh_msg.group_id == local_group_id) {
        deliver(&mesh_msg);  // callback or message queue
    }

    // Relay regardless of group membership.
    if (mesh_now_can_relay(&mesh_msg)) {
        mesh_now_relay_broadcast(&mesh_msg, true);
    }
}

Group ID Reference

Use Cases

• Department channels: each department gets a group ID
• Event coordination: temporary groups for events
• Access control: nodes only process messages for their group
• Multi-tenant meshes: shared infrastructure, isolated communication

Limitations

• A node can only be in one group at a time
• Group membership is local (not advertised to peers)
• There is no group discovery or registration protocol