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Information about Data Link Layer

OSI Model
7Application layer
6Presentation layer
5Session layer
4Transport layer
3Network layer
2Data link layer
1Physical layer
The data link layer is layer two of the seven-layer OSI model as well as of the five-layer TCP/IP reference model. It responds to service requests from the network layer and issues service requests to the physical layer.

This is the layer which transfers data between adjacent network nodes in a wide area network or between nodes on the same local area network segment. The data link layer provides the functional and procedural means to transfer data between network entities and might provide the means to detect and possibly correct errors that may occur in the Physical layer. Examples of data link protocols are Ethernet for local area networks and PPP, HDLC and ADCCP for point-to-point connections.

The data link is all about getting information from one place to a selection of other places. At this layer one does not need to be able to go everywhere, just able to go somewhere else. It is analogous to social interaction in that one needs to be able to talk to Bob to get a message to Fred or James.

The data link provides data transfer across the physical link. That transfer might or might not be reliable; many data link protocols do not have acknowledgments of successful frame reception and acceptance, and some data link protocols might not even have any form of checksum to check for transmission errors. In those cases, higher-level protocols must provide flow control, error checking, and acknowledgments and retransmission.

In some networks, such as IEEE 802 local area networks, the data link layer is split into MAC and 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 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

Logical Link Control Sublayer

The uppermost sublayer is Logical Link Control (LLC). This sublayer multiplexes protocols running atop the data link layer, and optionally provides flow control, acknowledgment, and error recovery. The LLC provides addressing and control of the data link. It specifies which mechanisms are to be used for addressing stations over the transmission medium and for controlling the data exchanged between the originator and recipient machines.

Media Access Control Sublayer

The sublayer below it is Media Access Control (MAC). Sometimes this refers to the sublayer that determines who is allowed to access the media at any one time (usually CSMA/CD). Other times it refers to a frame structure with MAC addresses inside. There are generally two forms of media access control: distributed and centralized. Both of these may be compared to communication between people:
  • In a network made up of people speaking, i.e. a conversation, we look for clues from our fellow talkers to see if any of them appear to be about to speak. If two people speak at the same time, they will back off and begin a long and elaborate game of saying "no, you first".
The Media Access Control sublayer also determines where one frame of data ends and the next one starts. In a snail-mail network, each letter is one frame of data, and one can tell where it begins and ends because it is inside an envelope. One might also specify that a letter will begin with a phrase like "Dear Sir", and ends with a phrase like "Yours faithfully".

List of Data link layer services

Examples

Interfaces

The data link layer is often implemented in software as a "network card driver". The operating system will have a defined software interface between the data link and the network transport stack above. This interface is not a layer itself, but rather a definition for interfacing between layers. Examples include:
  • ODI
  • NDIS
  • SANA II - Standard Amiga Networking Architecture, version 2
Open Systems Interconnection Basic Reference Model (OSI Reference Model or OSI Model for short) is a layered, abstract description for communications and computer network protocol design, developed as part of the Open Systems Interconnection (OSI) initiative.
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application layer is the seventh level of the seven-layer OSI model. It interfaces directly to and performs common application services for the application processes; it also issues requests to the presentation layer.
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presentation layer is the sixth level of the seven layer OSI model. It responds to service requests from the application layer and issues service requests to the session layer.
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session layer is level five of the seven level OSI model. It responds to service requests from the presentation layer and issues service requests to the transport layer.

The Session layer provides the mechanism for managing the dialogue between end-user application processes.
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transport layer is the second highest layer in the four and five layer TCP/IP reference models, where it responds to service requests from the application layer and issues service requests to the Internet layer.
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network layer is the third layer out of seven in OSI model and the third layer out of five in TCP/IP model. In the TCP/IP reference model it is called the Internet layer.
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Media Access Control (MAC) data communication protocol sub-layer, also known as the Medium Access Control, is a part of the data link layer specified in the seven-layer OSI model (layer 2).
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physical layer is level one in the seven-level OSI model of computer networking as well as in the five-layer TCP/IP reference model. It performs services requested by the data link layer.
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Open Systems Interconnection Basic Reference Model (OSI Reference Model or OSI Model for short) is a layered, abstract description for communications and computer network protocol design, developed as part of the Open Systems Interconnection (OSI) initiative.
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The TCP/IP model or Internet reference model, sometimes called the DoD model (DoD, Department of Defense) ARPANET reference model, is a layered abstract description for communications and computer network protocol design.
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network layer is the third layer out of seven in OSI model and the third layer out of five in TCP/IP model. In the TCP/IP reference model it is called the Internet layer.
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physical layer is level one in the seven-level OSI model of computer networking as well as in the five-layer TCP/IP reference model. It performs services requested by the data link layer.
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Wide Area Network (WAN) is a computer network that covers a broad area (i.e., any network whose communications links cross metropolitan, regional, or national boundaries [1]).
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local area network (LAN) is a computer network covering a small geographic area, like a home, office, or group of buildings. The defining characteristics of LANs, in contrast to Wide Area Networks (WANs), include their much higher data transfer rates, smaller geographic range, and
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A network segment is a portion of a computer network where in every device communicates using the same physical layer. Devices that extend the physical layer, such as repeaters or hubs, are also considered to extend the segment.
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Transfer may refer to:
  • Decal
  • Electron transfer
  • Jacoby transfer, a bidding device in contract bridge
  • ]
  • Knowledge transfer
  • Language transfer, where native language grammar and pronunciation influence the learning and use of a second language

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Ethernet is a family of frame-based computer networking technologies for local area networks (LANs). The name comes from the physical concept of the ether. It defines a number of wiring and signaling standards for the physical layer, through means of network access at the Media
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In networking, the Point-to-Point Protocol, or PPP, is a data link protocol commonly used to establish a direct connection between two nodes over serial cable, phone line, trunk line, cellular telephone, specialized radio links, or fiber optic links.
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In computer networking, a frame is a data packet of fixed or variable length which has been encoded by a data link layer communications protocol for digital transmission over a node-to-node link.
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Not to be confused with control flow.
In computer networking, flow control is the process of managing the rate of data transmission between two nodes.
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IEEE 802 refers to a family of IEEE standards dealing with local area networks and metropolitan area networks. More specifically, the IEEE 802 standards are restricted to networks carrying variable-size packets.
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IEEE 802.2 is the IEEE 802 standard defining Logical Link Control (LLC), which is the upper portion of the data link layer for local area networks. The LLC sublayer presents a uniform interface to the user of the data link service, usually the network layer.
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Token ring local area network (LAN) technology was conceived in the late 1960s by Olof Söderblom, then working for IBM [1] ). US Patents were awarded in 1981 and Token-Ring was developed and promoted by IBM in the early 1980s and standardized as IEEE 802.
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IEEE 802.11 is a set of standards for wireless local area network (WLAN) computer communication, developed by the IEEE LAN/MAN Standards Committee (IEEE 802) in the 5 GHz and 2.4 GHz public spectrum bands.

Although the terms 802.
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Fiber distributed data interface (FDDI) provides a standard for data transmission in a local area network that can extend in range up to 200 kilometers (124 miles). Although FDDI protocol is a token ring network, it does not use the IEEE 802.
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insufficient context for those unfamiliar with the subject matter.
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The introduction to this article provides insufficient context for those unfamiliar with the subject matter.
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In electronics, telecommunications and computer networks, multiplexing (short muxing) is a term used to refer to a process where multiple analog message signals or digital data streams are combined into one signal. The aim is to share an expensive resource.
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Media Access Control (MAC) data communication protocol sub-layer, also known as the Medium Access Control, is a part of the data link layer specified in the seven-layer OSI model (layer 2).
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