Ethernet can be divided into 2 sublayers; MAC and LLC. For WAN protocols like PPP, HDLC and frame relay, it is not discussed in regards to protocol sublayer for media access control. On serial interface, the encapsulation can be chosen from PPP, HDLC, frame relay, etc.
My question is, do WAN protocols like PPP, HDLC and frame relay have their own media access control protocol or do they use the same media access control protocol?
Best Answer
No, PPP, HDLC, FR do not have their own MAC. In the OSI model, MAC is associated with layer 2. PPP, HDLC, FR are on L2 as well. But LLC is associated with L1, the physical layer. MAC is not just a theoretical concept like a sublayer, MAC is a protocol by itself. There are many LLC protocols, but there is only one MAC, with the exception of a VLAN tag field.
Let us have a look at the third and the fourth field of a MAC portion of an Ethernet frame: Destination MAC Address; Source MAC Address. An address is 6 bytes long. In comparison, an HDLC address is 1 byte long. FR and PPP frames reach their destination very differently from MAC or HDLC.
In a nutshell, Ethernet formats network data on both L2 and L1, while PPP, HDLC, FR stay on L2. That is why none of them needs an extra sublayer.