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Data link layer
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<p>The data link layer, or layer 2, is the second layer of the seven-layer <a href="/facts/OSI_model/oxN9Xhjz">OSI model</a> of <a href="/facts/Computer_network/3w5RM99p">computer networking</a>. This layer is the protocol layer that transfers data between nodes on a <a href="/facts/Network_segment/D0gAdNdR">network segment</a> across the <a href="/facts/Physical_layer/WuATCrVw">physical layer</a>. The data link layer provides the functional and procedural means to <a href="/facts/Transfer_(computing)/fgBCc5U9">transfer</a> data between network entities and may also provide the means to detect and possibly correct errors that can occur in the physical layer. </p><p>The data link layer is concerned with local delivery of <a href="/facts/Frame_(networking)/ltGCbJIq">frames</a> between nodes on the same level of the network. Data-link frames, as these <a href="/facts/Protocol_data_unit/UJMVQEt9">protocol data units</a> are called, do not cross the boundaries of a local area network. Inter-network routing and global addressing are higher-layer functions, allowing data-link protocols to focus on local delivery, addressing, and media arbitration. In this way, the data link layer is analogous to a neighborhood traffic cop; it endeavors to arbitrate between parties contending for access to a medium, without concern for their ultimate destination. When devices attempt to use a medium simultaneously, frame collisions occur. Data-link protocols specify how devices detect and recover from such collisions, and may provide mechanisms to reduce or prevent them. </p><p>Examples of data link protocols are <a href="/facts/Ethernet/nMfhU8tU">Ethernet</a>, the <a href="/facts/IEEE_802.11/ryEGu6Vq">IEEE 802.11</a> WiFi protocols, <a href="/facts/Asynchronous_Transfer_Mode/SzA8ewFL">ATM</a> and <a href="/facts/Frame_Relay/bFdv0qIP">Frame Relay</a>. In the <a href="/facts/Internet_Protocol_Suite/KNkxtSpw">Internet Protocol Suite</a> (TCP/IP), the data link layer functionality is contained within the <a href="/facts/Link_layer/pHRpQ3k7">link layer</a>, the lowest layer of the descriptive model, which is assumed to be independent of physical infrastructure. </p>