The data link layer is the second layer of the OSI model. It handles the transmission of data frames over a physical link using flow control, error detection, and synchronization. The data link layer is divided into the media access control (MAC) sublayer, which regulates how data is moved between network interfaces, and the logical link control (MAC) sublayer, which controls frame synchronization, flow control, and error checking. Common data link layer protocols include Ethernet, Token Ring, Wi-Fi, ATM, and PPP.

1. By: Bharat Kunwar

2.  It is a second layer of the seven OSI layer
Model.
 It handles the moving of data in and out across
a physical link in a network.
 It provides reliable data transfer by transmitting
packets with the necessary synchronization,
error control and flow control.
 Data link layer is divided into two sub
layers: Media access control (MAC) and
Logical link control (LLC) layer.

3.  It is used to transfer data between network
nodes that are in a wide area network, or
between nodes which lie on the same local area
network segment.
 Provide service interface to the network layer
 Dealing with transmission errors
 Regulating data flow

4.  Ethernet
 Token Ring
 FDDI(Fiber Distributed Data Interface)
 IEEE 802.11 (WLAN, Wi-Fi)
 ATM(Asynchronous Transfer Mode)
 PPP(Point-to-Point Protocol)
 HDLC(High-Level Data Link Control)
 MPLS(Multiprotocol Label Switching)
 ADCCP (Advanced Data Communication
Control Procedures)

5.  Bridges
 Switches
 Hubs
 Router
 Distributed Interactive
Simulation protocol
data unit
 Frame (networking)
 MAC protocol data
unit
 Network packet
 Smart card
application protocol
data unit

6. The Media Access Control (MAC) sublayer:
o Media Access Control Layer is one of two
sublayers that make up the Data Link Layer of
the OSI model.
o The MAC layer is responsible for moving
data packets to and from one Network Interface
Card(NIC) to another across a shared channel.
The Logical Link Control (LLC) sublayer:
o Logical Link Control layer is one of two sublayers
that make up the Data Link Layer of the OSI
model.
o The Logical Link Control layer controls frame
synchronization, flow control and error checking.

7. Function of MAC:
 Protection against errors, generally by means of
generating and checking frame check
sequences
 Control of access to the physical transmission
medium
Function of LLC:
 Accepts data from higher layers and forms it into
standard frames
 Recognizes and deals with frame errors

8. Packets: Packet is one unit of binary data capable of
being routed through a computer network. To improve
communication performance and reliability, each
message sent between two network devices is often
subdivided into packets by the underlying hardware and
software.
Frame: Frame is data that is transmitted between
network points as a unit complete with addressing and
necessary protocol control information. A frame is
usually transmitted serial bit by bit and contains a
header field and a trailer field that "frame" the data.
(Some control frames contain no data.)

9. Segment: Segment is a specially-configured
subset of a larger network. The boundaries of a
network segment are established by devices
capable of regulating the flow of packets into and
out of the segment, including routers, switches,
hubs, bridges, or multi-homed gateways (but not
simple repeaters).