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Presentation of computer network on data link layer
1. PRESENTATION OF
COMPUTER NETWORK
ON DATA LINK LAYER
& SERVICE PROVIDED BY LINK LAYER
Presented by :
Sumit Gyawali & Akrosh Tiwari
Roll No: 301&325
Level:Bsc csit /Third year/fifth sem
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2. OVERVIEW
• Definition of data link layer
• Layer of data link layer
• Data link layer design issues
• Service provided by link layer
• Implementation
• Reference
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3. DATA LINK LAYER
• It is the second layer in OSI model.
• It transfer data from network layer of one machine to the network layer of another.
• Convert the raw bit stream of the physical layer into group of bits(frames).
• It is used for the encoding, decoding and logical organization of data bits. Data
packets are framed and addressed by this layer, which has two sublayers.
• The data link layer's first sublayer is the media access control (MAC) layer which
is used for source and destination addresses. It allows the data link layer to
provide the best data transmission vehicle and manage data flow control.
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5. CONTINUE..
• The data link layer's second sublayer is the logical link control. It manages
error checking and data flow over a network.
• This layer frame includes source and destination addresses, data length, start
signal or indicator and other related Ethernet information to enhance
communication. This layer's main responsibility is to transfer data frames
between nodes over a network.
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7. DATA LINK LAYER DESIGN ISSUES
• Providing a well-defined service interface to the network layer.
• Dealing with transmission errors.
• Regulating the flow of data so that slow receivers are not swamped by fast
senders.
• It takes the packets it gets from the network layer and encapsulates them into
frames for transmission. Each frame contains a frame header, a payload field
for holding the packet, and a frame trailer.
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8. SERVICES PROVIDED TO THE NETWORK LAYER
• The function of the data link layer is to provide services to the network layer. The
principal service is transferring data from the network layer on the source machine
to the network layer on the destination machine.
• The data link layer can be designed to offer various services. The actual services
offered can vary from system to system. Three reasonable possibilities that are
commonly provided are:
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9. UNACKNOWLEDGED CONNECTIONLESS SERVICE
• Unacknowledged connectionless service consists of having the source
machine send independent frames to the destination machine without having
the destination machine acknowledge them.
• No logical connection is established before hand or released afterward. If a
frame is lost due to noise on the line, no attempt is made to detect the loss or
recover from it in the data link layer
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10. ACKNOWLEDGED CONNECTION-ORIENTED SERVICE
• Here, the source and destination machines establish a connection before any data are
transferred. Each frame sent over the connection is numbered, and the data link layer
guarantees that each frame sent is indeed received. Furthermore, it guarantees that
each frame is received exactly once and that all frames are received in the right order.
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11. ACKNOWLEDGED CONNECTIONLESS SERVICE
• When this service is offered, there are still no logical connections used, but
each frame sent is individually acknowledged.
• In this way, the sender knows whether a frame has arrived correctly. If it has
not arrived within a specified time interval, it can be sent again. This service
is useful over unreliable channels, such as wireless systems.
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12. SERVICE PROVIDED BY LINK LAYER
- Link layer protocol is used to move a datagram over an individual link.
- It defines the format of the packets exchanged between the nodes at the ends
of the link,as well as actions taken by these nodes when packets are sent and
received.
It includes following service:
• Framing:
The Group of physical layer bit stream into units called frames.Divides the
data from N/w layer into frames.
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13. It consists data field in which network layer datagram is inserted and header
files also include trailer fields.
• Physical Addressing:
Add a header to the frame to define the physical address of the source and
the destination machines.
• Flow control:
It is the traffic regulatory mechanism implemented by data link layer that
prevents the fast sender from drawning the slow receiver.
Prevent a fast sender from overwhelming a slower receiver.
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14. • Error control:
It provides the mechanism of error control in which it detects and retransmits
damaged or lost frames.
Sender checksums the frame and transmits checksum together with data.
Receiver re-computes the checksum and compares it with the received value.
Error Detecting : Include enough redundancy bits to detect errors and use
VRC,LRC,CRC and retransmissions to recover from the errors.
Error Correcting : Include enough redundancy to detect and correct errors.
The use of error-correcting codes is often referred to as forward error
correction.
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15. • Reliable delivery:
It guarantees to move each network layer datagram across the link without error.
It is used for links that are prone to high error rates ,such as wireless link with goal
of correcting an error locally where error occurs.
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16. • Half- duplex and full –duplex:
With full duplex transmission,the nodes at both ends of a link may transmit
packets at same time.with half-duplex transmission,a node cannot both
transmit and receive at same time.
• Feedback:
After Transmitting the frames,the system waits for the feedback.
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17. IMPLEMENTATION OF DATA LINK LAYER
• In each and every host link layer implemented in “ network adapter”, also known
as network interface card (NIC ).
• It implements link layer services such as framing, link access ,flow control, error
detection.
Ethernet card, PCMCI card, 802.11 card
implements link, physical layer
• attaches into host’s system buses
• combination of hardware, software, firmware
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