Graphic design python turtle 🐢

By Kajal Vishwakarma -
from turtle import * import colorsys bgcolor('black') pensize(0) tracer(50) h=0 for i in range(300): c=colorsys.hsv_to_rgb(h,1,1) h+=0.9 color(c) forward(300) left(100) fd(i) goto(0,0) down() rt(90) begin_fill() circle(0) end_fill() rt(10) for j in range(5): rt(30) done() Please follow my blog and subscribe my channel for more videos and newly updates 👍👍👍👍👍 import turtle as t import colorsys t.bgcolor('black') t.tracer(100) h=0.4 def draw(ang,n): t.circle(5+n,60) t.left(ang) t.circle(5+n,60) for i in range(200): c=colorsys.hsv_to_rgb(h,1,1) h+=0.005 t.color(c) t.pensize(2) draw(90,i*2) draw(120,i*2.5) draw()
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Data Link Layer & it's Design Issues

By Kajal Vishwakarma -

 

Data Link Layer

Data link layer is the second layer of the open system interconnection (OSI) reference model. The  data link layer together with physical layer and the interconnecting medium provide a data link connection for reliable transfer of data bits over an imperfect physical connection. It improves the bit transport service of the physical layer by controlling the errors. The data link layer includes error control, flow control and the associated link management functions. This layer receives the data from the next higher layer and adds some control bits to a block of data bits to transfer to the other devices. The block of data along with the control bits is called frame, which is handed over to the physical  layer. The physical layer convert the bit into an electrical signal for transmission over the interconnecting transmission medium. The electrical signal is converted back to bits form by the physical layer at the receiving side and the frame is handed over to the data link layer. The data link layer removes the control bits and checks for errors. It hands over the received data bits to the next layer when no error is found.

 

The design issues for data link layer are discussed below:-

  • 1)      Services Provided to the Network Layer

a)      Unacknowledged Connectionless Service

b)      Acknowledge Connectionless Service

c)       Acknowledge Connection-oriented Service

  • 2)      Framing
  • 3)      Error Control
  • 4)      Flow Control
  • 5)      Physical Addressing

 

  • 1)      Services Provided to the Network Layer:-The primary responsibility of data link layer is to provide services to the network layer. The principle service is transferring data from the network layer on the source machine to the network  layer on the destination machine. The two data link layers communicate with each other by data link control protocol.

         Following are the important services provided by data link layer to the network  layer:-

 

a)      Un acknowledge Connectionless Service:- As the name suggest it is unknowledge form of transmission. Here, the source machine sends the data to the destination machine without any acknowledgement. For this, no connection is either established or released. If the data is lost due to noise or interference, the lost data is not even recovered by the layer.

b)      Acknowledge Connectionless Service:-  In acknowledge connectionless service each data frame is acknowledge by the destination machine. If any data frame is lost or not arrived in time, the same can be transmitted again. In this service no connections are used.

c)       Acknowledge Connection-oriented Service:-  Acknowledge connection-oriented service establishes a connection prior to data transmission. Each frame is numbered before transmission and corresponding acknowledgement is also received. The transmission is  carried out in distinct phases.


  • 2)   Framing:- To service the network layer, data link layer uses the service provided to it by the physical layer. Physical layer accepts the raw bit stream and delivers it to destination. This bit stream may contain error i.e., number of bits received may not be equal to number of bits transmitted. various simple methods used for framing are-

a)      Character count

b)      Starting and ending character, with character stuffing

c)       Starting and ending flags, with bit stuffing.


  • 3)      Error Control:-  To ensure the proper sequencing and safe delivery of frames at the destination, an acknowledgement should be sent by the destination network. The receiver sends back special control frames bearing positive or negative acknowledgements about the incoming frames.

  • 4)      Flow control:-  When the sender is running on fast machine or lightly loaded machine and receiver is on slow or heavily loaded machine, then the transmitter will transmit frames faster than the receiver can accept them. Even if the transmission is error free at a certain point the receiver will simply not be able to handle the frames as they arrive and will start to lose some. The most common retransmission technique is known as Automatic Repeat request (ARQ).

  • 5)      Physical Addressing:-  If frames are to be distributed two different systems on the network, the data link layer adds a header to the frame to define the physical address of sender and/or receiver of the frame.

 

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