Atmel LwMesh: How is the MAC layer implemented?

[agm30]

I'm confused about the implementation of MAC layer on Atmel's LwMesh Posts by @alexru says that 

1. "LwMesh uses IEEE 802.15.4 physical frames, but it does not follow IEEE 802.15.4 MAC specification, so it is "worse" than the real MAC in this sense. But LwMesh implements mesh routing, so it is "better" than plain MAC in that respect" . 
2. "LwMesh uses standard MAC header (to facilitate hardware frame filtering), but does not respond to the command frames"
3. "You don't need MAC with LwMesh"
 
Now the MAC protocol usually provides the fully functionalities
1. Framing - define the frame format and perform data encapsulation
2. Medium access - control which device can access the medium, avoid collisions etc using some modification of CSMA/CA
3. Reliability - ensure successful transmission through ACKs
4. Flow control - moderate buffers
5. Error control - error detection etc.

Questions.

1. How much of this does the LwMesh do?
2. Why doesn't LwMesh need MAC?
3. How is it handling channel access?
4. Can LwMesh be classified as a cross-layer protocol?[/li][/list]

 
The LWM architecture shows a HAL, PHY and then directly a NWK layer. The code base also has no mention of MAC layer.
 
Can somebody give a definitive answer to this? Thank you.

[ataradov]

Now the MAC protocol usually provides the fully functionalities
1. Framing - define the frame format and perform data encapsulation
2. Medium access - control which device can access the medium, avoid collisions etc using some modification of CSMA/CA
3. Reliability - ensure successful transmission through ACKs
4. Flow control - moderate buffers
5. Error control - error detection etc.

That is if you read a lot of school books. Actually all of that is done by the PHY / radio itself. MAC is a fancy abstraction on top of that, from people that like fancy abstractions. Separate MAC layer is needed when you try to specify a universal interface for any number of higher layers. In this case IEEE designed MAC interface and they don't care who uses it. LwMesh is all in one package, so MAC layer can be omitted.

Doing layers - is how you get bloat and happy academics.

1. How much of this does the LwMesh do?

All of the above.

2. Why doesn't LwMesh need MAC?
3. How is it handling channel access?

Though CSMA/CA performed by the transceiver.

4. Can LwMesh be classified as a cross-layer protocol?

Classifications are mostly pointless, so yeah, sure, why not.
 

The LWM architecture shows a HAL, PHY and then directly a NWK layer. The code base also has no mention of MAC layer.

Network layer is handling  everything.