Computer Networks Framing

We will skip the physical layer and the detail of how communication signals are sent and received. In doing so, we are simply going to assume (a correct assumption) that we are capable of sending bits over a single link. Using this abstraction, the DLC layer becomes responsible for reliable transmission of packets over a single link. Reliable transmission of packets means that every packet is delivered once, only once, without errors, and in order. To achieve this goal, the DLC layer performs three operations: • Framing: determines start and end of packets (all we see is a string of bits) and their order by inserting packet headers • Error detection: determines when errors exist using packet trailers • Error correction: retransmits packets containing errors