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In the LoRa frame,
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The field PHY payload carries the upper layer protocol. 
And in our case, the protocol carried by the LoRa
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packet is the LoRa MAC,
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so the LoRaWAN protocol.
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Let's see what's in there.
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If we look at the specification, we can see that the PHY payload is composed of three fields: A MAC Header,
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a MAC Payload, and a MIC.
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The MAC Header is used to indicate the type of frame (a Join, Data up or down, if it's confirmed or unconfirmed...
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and so on.)
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It's been calculated on the device and will be checked on the server.
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Great.
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So now, we can ask ourselves what is in the MAC payload?
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Well, in the MAC payload there is another header called Frame Header, a field called Frame Port, and
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the last field call Frame Payload.
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The Frame Header contains many useful information like the device adress for identification in the
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network.
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The Frame Counter that we explained earlier used for replay attack and a few other information to indicate
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if the device needs to use the ADR algorithm.
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If the frame is acknowledging a previous transmission and so on.
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But between all these fields, the most important one for the end user is the Frame Payload. Because
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it's the user data.
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So here, we have the overall LoRaWAN frame and the user data is in the top right corner of my figure.
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But there is one last thing to explain, because right now if we read the Frame Payload in this LoRa frame,
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then there is no way to understand its content because it's encrypted.
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That will be the job of the last layer, which is the Application Layer.
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And we'll see that in the next video.