[ Computer Network ]
[ Unit 3 ]
[ Data Link Layer ]
In the OSI model, the data link layer is a 4 th layer from the top and 2nd layer from
the bottom.
The communication channel that connects the adjacent nodes is known as links, and
in order to move the datagram from source to the destination, the datagram must
be moved across an individual link.
The main responsibility of the Data Link Layer is to transfer the datagram across
an individual link.
The Data link layer protocol defines the format of the packet exchanged across
the nodes as well as the actions such as Error detection, retransmission, flow
control, and random access.
,The Data Link Layer protocols are Ethernet, token ring, FDDI and PPP.
An important characteristic of a Data Link Layer is that datagram can be handled
by different link layer protocols on different links in a path. For example, the
datagram is handled by Ethernet on the first link, PPP on the second link.
Sub-layers of Data Link Layer:
The data link layer is further divided into two sub-layers, which are as follows:
Logical Link Control (LLC):
This sublayer of the data link layer deals with multiplexing, the flow of data
among applications and other services, and LLC is responsible for providing error
messages and acknowledgments as well.
Media Access Control (MAC):
MAC sublayer manages the device’s interaction, responsible for addressing
frames, and also controls physical media access.
The data link layer receives the information in the form of packets from the
Network layer, it divides packets into frames and sends those frames bit-by-bit
to the underlying physical layer.
, Functions/services of the Data-link Layer :
1. Framing:
The packet received from the Network layer is known as a frame in the
Data link layer. At the sender’s side, DLL receives packets from the Network
layer and divides them into small frames, then, sends each frame bit-by-bit to
the physical layer. It also attaches some special bits (for error control and
addressing) at the header and end of the frame. At the receiver’s end, DLL takes
bits from the Physical layer organizes them into the frame, and sends them to the
Network layer.
2. Addressing:
The data link layer encapsulates the source and destination’s MAC address/
physical address in the header of each frame to ensure node-to-node delivery.
MAC address is the unique hardware address that is assigned to the device while
manufacturing.
[ Unit 3 ]
[ Data Link Layer ]
In the OSI model, the data link layer is a 4 th layer from the top and 2nd layer from
the bottom.
The communication channel that connects the adjacent nodes is known as links, and
in order to move the datagram from source to the destination, the datagram must
be moved across an individual link.
The main responsibility of the Data Link Layer is to transfer the datagram across
an individual link.
The Data link layer protocol defines the format of the packet exchanged across
the nodes as well as the actions such as Error detection, retransmission, flow
control, and random access.
,The Data Link Layer protocols are Ethernet, token ring, FDDI and PPP.
An important characteristic of a Data Link Layer is that datagram can be handled
by different link layer protocols on different links in a path. For example, the
datagram is handled by Ethernet on the first link, PPP on the second link.
Sub-layers of Data Link Layer:
The data link layer is further divided into two sub-layers, which are as follows:
Logical Link Control (LLC):
This sublayer of the data link layer deals with multiplexing, the flow of data
among applications and other services, and LLC is responsible for providing error
messages and acknowledgments as well.
Media Access Control (MAC):
MAC sublayer manages the device’s interaction, responsible for addressing
frames, and also controls physical media access.
The data link layer receives the information in the form of packets from the
Network layer, it divides packets into frames and sends those frames bit-by-bit
to the underlying physical layer.
, Functions/services of the Data-link Layer :
1. Framing:
The packet received from the Network layer is known as a frame in the
Data link layer. At the sender’s side, DLL receives packets from the Network
layer and divides them into small frames, then, sends each frame bit-by-bit to
the physical layer. It also attaches some special bits (for error control and
addressing) at the header and end of the frame. At the receiver’s end, DLL takes
bits from the Physical layer organizes them into the frame, and sends them to the
Network layer.
2. Addressing:
The data link layer encapsulates the source and destination’s MAC address/
physical address in the header of each frame to ensure node-to-node delivery.
MAC address is the unique hardware address that is assigned to the device while
manufacturing.
