Editing Data link layer (section)

==Function==
The data link provides for the transfer of [[data frame]]s between hosts connected to the physical link. Within the semantics of the OSI network architecture, the protocols of the data link layer respond to service requests from the [[network layer]], and perform their function by issuing service requests to the [[physical layer]]. That transfer can be [[Reliability (computer networking)|reliable or unreliable]]; many data link protocols do not have acknowledgments of successful frame reception and acceptance, and some data link protocols might not even perform any check for transmission errors.  In those cases, higher-level protocols must provide [[flow control (data)|flow control]], error checking, acknowledgments, and retransmission.

The frame header contains the source and destination addresses that indicate which device originated the frame and which device is expected to receive and process it.  In contrast to the hierarchical and routable addresses of the network layer, layer 2 addresses are flat, meaning that no part of the address can be used to identify the logical or physical group to which the address belongs.

In some networks, such as [[IEEE 802]] local area networks, the data link layer is described in more detail with [[media access control]] (MAC) and [[logical link control]] (LLC) sublayers; this means that the [[IEEE 802.2]] LLC protocol can be used with all of the IEEE 802 MAC layers, such as Ethernet, [[Token Ring]], [[IEEE 802.11]], etc., as well as with some non-802 MAC layers such as [[FDDI]].  Other data-link-layer protocols, such as [[High-Level Data Link Control|HDLC]], are specified to include both sublayers, although some other protocols, such as [[Cisco HDLC]], use HDLC's low-level framing as a MAC layer in combination with a different LLC layer. In the [[ITU-T]] [[G.hn]] standard, which provides a way to create a high-speed (up to 1 Gigabit/s) [[local area network]] using existing home wiring ([[Power line communication|power lines]], phone lines and [[Ethernet over coax|coaxial cables]]), the data link layer is divided into three sub-layers (application protocol convergence, logical link control and media access control).