[Year 12 SofDev] Software development key knowledge

[Timmer-Arends]

Hello again Heath

I didn't see the second question and since no one else appears to have responded (probably sensibly having a day off) I'll give it a go

Question: Is it possible to classify switches hubs and NICs into the physical layer because they are hardware and the cables plug into them, while the data travelling through these devices is on an upper level? Or is a NIC always on the data layer and switches somewhere between data and network layers?

Switches hubs etc cannot be placed in the physical layer simply because they are hardware - afterall the computer we transmit messages from is also hardware. It depends on what protocol issues they have to deal with (possibly via firmware programming). So
- hubs are purely layer 1 since all they do is send a received signal to all ports - they in effect just repeat the signal, they have no understanding of the content of that signal
- switches need to know which port to send received data down so they need to know about physical addressing within a network which means being able to read data link (layer 2) frames
- routers need to know about the end to end addressing so they operate up to the network layer (3)
- NICs transform computer 1's and 0's into whatever the transmission medium requires so they are definitely layer 1. But it could depend on the kind of network they connect into; for example, collision detection in Ethernet is done in hardware on the NIC, but I'm pretty sure that collision detection (and then dealing with it) is a layer 2 function - I stand to be corrected on this. Also NICs are responsible for MAC addresses which is a layer 2 function. 

I hope this is helpful

Regards
Robert T-A
Brighton SC


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