OSI Layer for Point to Point WANs

Point to Point WANs typically operate at the Data Link layer (Layer 2) of the OSI model. This is because point to point connections are established between two devices, and the Data Link layer is responsible for establishing and maintaining a reliable communication link between these devices.

The Data Link layer provides services such as framing, error detection and correction, flow control, and addressing. In the case of point to point WANs, these services are used to ensure that data is transmitted accurately and efficiently between the two connected devices.

Some common point to point WAN technologies that operate at the Data Link layer include High-Level Data Link Control (HDLC), Point-to-Point Protocol (PPP), and Serial Line Internet Protocol (SLIP). These protocols are used to encapsulate data packets into frames and provide the necessary control information for transmitting the frames across the point to point connection.

It is worth noting that some point to point WAN technologies may also operate at higher layers of the OSI model, depending on their specific implementation. For example, the MPLS VPN technology can operate at both the Data Link layer and the Network layer (Layer 3) of the OSI model.

WAN operates on layer 1 and 2 of the OSI model. PPP, HDLC etc.. all are Layer 2 protocols. Both WAN and LAN service arrange bits from the physical layer into logical sequences called frames. WANs implement the same OSI Layer 1 and Layer 2 functions with different mechanisms and details as compared to LANs.

Connection-oriented WAN data link protocols, in addition to framing, detect and may correct errors. They are also capable of controlling the rate of transmission. A WAN data link layer might implement a sliding window flow control and acknowledgment mechanism to provide reliable delivery of frames; that is the case for Synchronous Data Link Control (SDLC) and HDLC, and derivatives of HDLC such as LAPB and LAPD. The data link layer provides the functional and procedural means to transfer data between network entities and to detect and possibly correct errors that may occur in the physical layer. Originally, this layer was intended for point-to-point and point-to-multipoint media, characteristic of wide area media in the telephone system.