The link layer is a fundamental layer in digital communications that manages data links between the physical level and upper layers. It handles simplex, half-duplex, and full-duplex data links using framing techniques and has two sublayers: LLC and MAC. The LLC deals with flow control and error correction, while the MAC identifies the physical address of the device and schedules data packet delivery.
The link layer is one of the lowest and most fundamental conceptual layers in digital communications. Basically, it’s where all the logic to manage a data link resides. It operates in a kind of hierarchy, serving as an interface, in this case, between the lowest level, the physical level that transmits the raw flow of ones and zeros, and the upper layers. In many cases, the term is used interchangeably with “link layer,” which typically refers to the second layer of the Open Systems Interconnection (OSI) model, the data link layer, used in computer networks. There are a number of communication protocols that operate at the link layer, but its essential functions are to prepare data packets for transport as well as interpret any input over the data link.
There are three types of data links that a link layer must handle: simplex, half-duplex, and full-duplex. With a simplex link, data travels in one direction, like a broadcast network, where there is a dedicated sender and receiver, and the receiver doesn’t need to return anything to the sender. With half-duplex, data can go in both directions, but not simultaneously. Full-duplex communications allow data to travel in both directions at the same time, which requires more effort from the link layer to sort out the communications that come and go.
To do much of its work, the link layer uses a technique known as framing. This involves adding an additional identifier indicating where the frame begins or ends in the bitstream. While there are other framing methods, in most cases, this is simply an extra bit added to the stream during specific increments. On the receiving end, the link layer synchronizes frame bits in the stream to help separate frames, extract the original packets, and pass them on to other layers as needed. Synchronization between the sending and receiving ends is important, because if the receiving link layer detects flow between frames, it can simply wait for the next frame to start, discarding any unusable bits that don’t belong in a frame.
The data link layer of the OSI model also perceives two sublayers to the link layer. One is referred to as logical link control (LLC), while the other is media access control (MAC). The top sublevel LLC deals with issues such as flow control and error correction in transmission. Depending on the type of communication, some error correction methods may not be used. For example, with wireless networking, the link layer has the ability to request bad packets to be sent, which is much rarer in wired communications where the link layer is only concerned with detecting errors and dropping bad packets. valid.
The lower MAC sublayer is then responsible for identifying the physical address of the device, commonly referred to as the MAC address. It is also able to maintain the possible queuing of data packets, as well as to schedule their delivery and guarantee the quality of the transmission. This is also where frame synchronization occurs, as well as protocols that prevent stream collisions.
Protect your devices with Threat Protection by NordVPN
