Editing Data link layer (section)

{{Use American English|date = March 2019}}
{{Short description|Second layer of the OSI networking model}}
{{Use mdy dates|date = March 2019}}

{{OSIModel}}

The '''data link layer''', or '''layer 2''', is the second layer of the seven-layer [[OSI model]] of [[computer network]]ing. This layer is the protocol layer that transfers data between nodes on a [[network segment]] across the [[physical layer]].<ref>{{cite web|title=What is layer 2, and Why Should You Care?|url=http://www.accel-networks.com/blog/2009/09/what-is-layer-2-and-why-should-you-care.html|archive-url=https://web.archive.org/web/20100218075030/http://www.accel-networks.com/blog/2009/09/what-is-layer-2-and-why-should-you-care.html|archive-date=2010-02-18|publisher=accel-networks.com|access-date=2009-09-29}}</ref> The data link layer provides the functional and procedural means to [[transfer (computing)|transfer]] data between network entities and may also provide the means to detect and possibly correct errors that can occur in the physical layer.

The data link layer is concerned with local delivery of [[Frame (networking)|frames]] between nodes on the same level of the network.  Data-link frames, as these [[protocol data unit]]s 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.

Examples of data link protocols are [[Ethernet]], the [[IEEE 802.11]]  WiFi protocols, [[Asynchronous Transfer Mode|ATM]] and [[Frame Relay]]. In the [[Internet Protocol Suite]] (TCP/IP), the data link layer functionality is contained within the [[link layer]], the lowest layer of the descriptive model, which is assumed to be independent of physical infrastructure.