By: Bharat Kunwar

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.

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

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)

Bridges

Switches

Hubs

Router

Distributed Interactive

Simulation protocol

data unit

Frame (networking)

MAC protocol data

unit

Network packet

Smart card

application protocol

data unit

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.

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

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.)

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).