Studying the seven layers of the OSI design, a decision to be taken is that the layer three, also referred to as the network layer is the one which WAN protocols operates on. The network layer carries out regular tasks as well as pinpoints end-to-end addressing and routing datagrams (Regan, 2004). There exists a unit known as brouter that some layers incorporate which works like a router and a bridge. Routers and switches work on layers 2-4 (data link layer, network layer as well as transport layer). As mentioned earlier, on layer two of the OSI model, network layer, is the place where the addressing and routing is carried out. On the transport layer of the OSI model is the place where the flow control and mistake handling works. Lastly, on layer four the synchronizations and assemblies are completed.
Being made up of various parts each layer has a unique function in the network. Additionally, each layer incorporates things to the data which is transmitted from one point to the other. The protocols which work on this layer are HDLC, PPP as well as the frame relay protocol. HDLC protocol means High-Level Data Link Control protocol. An additional protocol which works on layers of the OSI model is the Point-to-Point protocol (PPP) that is just like HDLS protocol. The frame relay protocol works at the data links layer of the OSI model (Cisco, 2008).