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data link layers in computer networks, Lecture notes of Computer Networks

Ahmadabad UniversityComputer Networks

This paper overview the data link layer or the 2nd layer the OSI Model along with some of its protocols such as ethernet, which is widely used in communication today.The article begins with introducing OSI Model,then emphasizing on DLL and the services provided by it to the network layer and various techniques used for the data encapsulation, flow and error control with few examples.Some elementary Data Link protocols are also discussed along with Internet protocols. Lastly, it is concluded that

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Term paper of Computer Communication Network(EC106203EC)
DATA LINK LAYER OF OSI REFERENCE MODEL AND SOME OF ITS
PROTOCOLS
Submitted by: Ayushi Kumari
Roll Number :19116013
Enrolment Number:190540
Email: 711ayushibhagat@gmail.com
Date of Submission:29th April,2022
Submitted to:
Dr.Ajay Singh Raghuvanshi Sir
HOD Dept. of Electronics and Communication Engg. NITRR
Contact Email:asraghuvanshi.etc@nitrr.ac.in
ABSTRACT:
This paper overview the data link layer or the 2nd layer the OSI Model along with some of its
protocols such as ethernet, which is widely used in communication today.The article begins with
introducing OSI Model,then emphasizing on DLL and the services provided by it to the network
layer and various techniques used for the data encapsulation, flow and error control with few
examples.Some elementary Data Link protocols are also discussed along with Internet protocols.
Lastly, it is concluded that DLL plays a very important role in the OSI model.
INTRODUCTION:
OSI refers to Open Systems Interconnection. It was developed by ISO – ‘International
Organization for Standardization‘ in 1984. It is basically a 7 layer architecture and each layer has
specific services to provide.
The data link layer manages the
node-to-node delivery of the message.
The main function is to make sure that
the data transfer is error-free over the
physical layer. When a packet enters a
network, it's the responsibility of DLL to
transfer it to the Host using its MAC
address. The Data Link layer is handled
by the NIC (Network Interface Card)
and device drivers of host machines.
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Partial preview of the text

Download data link layers in computer networks and more Lecture notes Computer Networks in PDF only on Docsity!

Term paper of Computer Communication Network(EC106203EC)

DATA LINK LAYER OF OSI REFERENCE MODEL AND SOME OF ITS

PROTOCOLS

Submitted by: Ayushi Kumari Roll Number : Enrolment Number: Email: 711ayushibhagat@gmail.com Date of Submission:29th April, Submitted to: Dr.Ajay Singh Raghuvanshi Sir HOD Dept. of Electronics and Communication Engg. NITRR Contact Email:asraghuvanshi.etc@nitrr.ac.in

ABSTRACT:

This paper overview the data link layer or the 2nd layer the OSI Model along with some of its protocols such as ethernet, which is widely used in communication today.The article begins with introducing OSI Model,then emphasizing on DLL and the services provided by it to the network layer and various techniques used for the data encapsulation, flow and error control with few examples.Some elementary Data Link protocols are also discussed along with Internet protocols. Lastly, it is concluded that DLL plays a very important role in the OSI model.

INTRODUCTION:

OSI refers to Open Systems Interconnection. It was developed by ISO – ‘International Organization for Standardization‘ in 1984. It is basically a 7 layer architecture and each layer has specific services to provide. The data link layer manages the node-to-node delivery of the message. The main function is to make sure that the data transfer is error-free over the physical layer. When a packet enters a network, it's the responsibility of DLL to transfer it to the Host using its MAC address. The Data Link layer is handled by the NIC (Network Interface Card) and device drivers of host machines.

DATA LINK LAYER:

Data Link Layer is classified into two sublayers:

  1. Logical Link Control (LLC)
  2. Media Access Control (MAC) The packet obtained from the Network layer is categorized into frames on the basis of the frame size of NIC(Network Interface Card). DLL encapsulates Sender’s and Receiver’s MAC address in the header of the frames. The Receiver’s MAC address is acquired by running an ARP(Address Resolution Protocol) request onto the wire and the destination node will answer with its MAC address. FUNCTIONS OF DATA LINK LAYER: ● Framing: It is a way for the sender to transfer a set of bits that is valid to the receiver. This is done by attaching special bit patterns to the beginning as well as end of the frame.DLL converts the physical layers bit steam into discrete units called frames.Receiver recognises the end of frame by : ○ Character count: A field in the header is used to specify the number of characters in a frame,hence the receiver knows the end of the frame.But the problem is that the count can be distorted by a transmission error. ○ Flag byte with byte stuffing: It uses particular characters to imply the start and end of the frame. ○ Starting and ending flag with bit stuffing :This method allows frames to contain arbitrary numbers of bits and permits character codes with arbitrary number of codes per character. ○ Encoding violations:It is used on only those networks in which encoding on the physical medium has redundancy.Hence,Manchester coding is used.i.e. High-low pair(10) is 1 and low-high pair(01) is 0. ● Physical addressing: The DLL adds physical addresses (MAC address) of the sender and receiver in the header of every frame.

○ Rate-based flow control: It limits the rate at which sender sends data ,without feedback from the receiver. ● Access control: When a single communication channel is shared by multiple devices, the MAC sub-layer of the data link layer helps to determine which device has control over the channel at a given time.

Elementary Data Link Protocol:

The protocols are generally implemented by programming languages: ● Unrestricted Simplex Protocol: Data is transmitted in one direction only.The transmitting(Tx) and receiving (Rx) hosts are always ready.Processing time can be ignored.It has infinite buffer space available.It has no damaged frames and no lost frames. ● Simplex Stop-and-wait Protocol: The receiver can only process the received information at a finite rate. ● Simplex Protocol for a Noisy Channel

Sliding Window Protocols:

Data Frame Transmission: Unidirectional assumption protocol with: a. Full Duplex and separate channels for sending data and receiving acknowledgement. It is costly and sometimes reverse channel bandwidth is wasted. b. Full Duplex with same circuit for both data and acknowledgement. c. Full Duplex by attaching acknowledgement to outgoing data frames ,called piggybacking. It utilizes higher channel bandwidth.

Common Data Link Protocols:

● Synchronous Data Link Protocol (SDLC) − SDLC is a communication protocol. It generally allows multipoint links even in error recovery and error correction also. It is also used to manage SNA (Systems Network Architecture) traffic and is the current precursor to HDLC. It was developed by IBM in 1975. It connects all of the remote devices to the mainframe servers at central locations which can be in point-to-point (one-to-one) or point-to-multipoint (one-to-many) connections. It ensures that the data units arrive correctly and with the correct flow from one network point to the next network point. ● High Level Data Link Protocol (HDLC) − HDLC is a SDLC based protocol and provides both unreliable service and reliable service and the basis of many Wide Area Protocols. It is a basically a bit – oriented protocol that is suitable for both point – to – point and multipoint communications. It is included as a part of the X.25 network. It was designed by ISO in 1979. ● Serial Line Interface Protocol (SLIP) − It is a very simple protocol for sending data units between an Internet service provider (ISP) and home user via a dial-up link. But it cannot detect or correct errors. SLIP is basically an older protocol that is employed to add a framing byte at the end of an IP packet. SLIP is an encapsulation of the TCP/IP developed exclusively to work with over serial ports and several router connections for easy communication. ● Point - to - Point Protocol (PPP) − This is used to transfer multiprotocol data between two directly connected (point-to-point) computers. It is basically a byte – oriented protocol which is popularly employed in broadband communications that includes heavy loads and high speeds. It is generally used to provide the same functionality as SLIP. It is one of the most robust protocols which is deployed to transport other types of packets and IP Packets. It is also useful for dial-up and leased router-router lines. It generally allows a framing method to create frames. It is a character-oriented protocol and therefore used for error detection. It provides two protocols i.e. NCP and LCP. LCP allows for bringing

REFERENCE:

[1]https://en.wikipedia.org/wiki/Data_link_layer [2]https://cs.uwaterloo.ca/~tozsu/courses/CS755/course_notes/4.Data%20Link.pdf [3]https://www.router-switch.com/faq/data-link-layer-protocols.html [4]https://www.geeksforgeeks.org/layers-of-osi-model/ [5]https://www.geeksforgeeks.org/examples-of-data-link-layer-protocols/