Data Link Layer | Layer 2 | The OSI-Model

OSI Layer 2 – Data Link Layer

The data link layer or layer 2 is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between adjacent network nodes in a wide area network (WAN) or between nodes on the same local area network (LAN) segment.[1] 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.

The data link layer is concerned with local delivery of frames between devices on the same LAN. Data-link frames, as these protocol data units are called, do not cross the boundaries of a local network. Inter-network routing and global addressing are higher-layer functions, allowing data-link protocols to focus on local delivery, addressing, and media arbitration. 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 for local area networks (multi-node), the Point-to-Point Protocol (PPP), HDLC and ADCCP for point-to-point (dual-node) connections. 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.Common hardware on this layer: Bridge, Switch (Multiport bridge)

Wikipedia

Services

• Encapsulation

• Frame synchronization

• Logical link control (Error & Flow control)

• Media access control (MAC, LAN switching, Physical addressing, QaS, VLAN, …)

Popular Data Link Layer Protocols

ARP

Address Resolution Protocol

ARCnet

ATM

CDP

Cisco Discovery Protocol

CAN

Controller Area Network

Econet

Ethernet

EAPS

Ethernet Automatic Protection Switching

FDDI

Fiber Distributed Data Interface

Frame Relay

HDLC

High-Level Data Link Control

IEEE 802.2

provides LLC functions to IEEE 802 MAC layers

IEEE 802.11

wireless LAN

I²C

LattisNet

LAPD

Link Access Procedures, D channel

LLDP

Link Layer Discovery Protocol

LocalTalk

MIL-STD-1553

MPLS

Multiprotocol Label Switching

NDP

Nortel Discovery Protocol

SDN

OpenFlow

PPP

Point-to-Point Protocol

Profibus

SpaceWire

SLIP

Serial Line Internet Protocol (obsolete)

SMLT

Split multi-link trunking

IEEE 802.1aq

Shortest Path Bridging

Spanning Tree Protocol

StarLan

Token ring

UDLD

Unidirectional Link Detection

UNI/O

1-Wire

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