These are the following steps to design a 2 bit synchronous down counter using T Flip flop:

Step 1: To design synchronous down counter, we just require to change the order of present state and next state, just put 0 where is 1 in synchronous up counter. In other words, start from 11 (3) to 00 (0)

Step 2: After that, we need to construct a state table with excitation table.
Note: To construct excitation table from state table you should know the excitation table of respective flip flop, in this case, it is T flip flop. So check the excitation table forT flip flop Which is:

T Flip Flop Excitation Table

Present state	Next State	T
0	0	0
0	1	1
1	0	1
1	1	0

So, the above table is the excitation table for T Flip Flop.

State Table with  excitation  table

Present State		Next State		Flip Flop
Q2	Q1	Q'2	Q'1	T2	T1
0	0	1	1	1	1
0	1	0	0	0	1
1	0	0	1	1	1
1	1	1	0	0	1

Above the table is created as per follow :

When Q₂ =1 which is present state and Q₂‘=1 which is next state then T₂ become 0 [As per excitation table, have a look ]
Similarly, if Q₂ is 1and Q₂‘ is 0 then T_{2 becomes} 1.
In a similar way, it goes on.

Step 3: After making the excitation table the next thing to do is dig out the equation from the boolean algebra or K map for the design of the counter. So For T₁ and T₂ we got 1 and Q₁‘ .

K-Map

 

For T_{2  Flip flop,}

 

 

 

 

T₂= Q₁‘

For T₁ Flip flop,

 

T₁=1

Step 4: Lastly according to the equation got from K map create the design for 2 bit synchronous down counter.

In above design T₁ is getting high input  and T₂ is getting input from the output of the T₁ which is complement of the output.  A clock is attached to it which is always high in blue color.

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Design a 2 bit Synchronous up counter using T Flip flop?

These are the following step to design a 2 bit Synchronous up counter using T Flip flop

Step 1: To design a synchronous up counter, first we need to know what number of flip flops are required. we can find out by considering a number of bits mentioned in the question. So, in this, we required to make 2 bit counter so the number of flip flops required is 2 [2ⁿ where n is a number of bits].

Step 2: After that, we need to construct a state table with an excitation table.

Note: To construct an excitation table from the state table you should know the excitation table of the respective flip flop, in this case, it is T flip flop. So check the excitation table forT flip flop Which is:

T Flip Flop Excitation Table

So, the above table is the excitation table for T Flip Flop.

State Table with  excitation  table

Above the table is created as per follow :

When Q₂ =0 which is the present state and Q₂‘=0 which is the next state then T₂ becomes 0 [As per excitation table, have a look ]
Similarly, if Q₂ is 0 and Q₂‘ is 1 then T_{2 becomes} 1.
In a similar way, it goes on.

Step 3: After making the excitation table the next thing to do is dig out the equation from the boolean algebra or K map for the design of the counter. So For T₁ and T₂ we got 1 and Q₁ .

K-Map

For T_{2  Flip flop,}

For T₁ Flip flop,

Step 4: Lastly according to the equation got from K map create the design for 2 bit synchronous up counter.

In the above design, T₁ is getting high input and T₂ is getting input from the output of the T₁ flip flop.  A clock is attached to it which is in blue colour.

These are the following steps to Design a 3 bit synchronous up counter using T Flip flop:

Step 1: To design a synchronous up counter, first we need to know what number of flip flops are required. we can find out by considering a number of bits mentioned in the question. So, in this, we required to make 3 bit counter so the number of flip flops required is 3 [2ⁿ where n is a number of bits].

Step 2: After that, we need to construct state table with excitation table.
Note: To construct excitation table from state table you should know the excitation table of respective flip flop, in this case, it is T flip flop. So check the excitation table for T flip flop Which is:

T Flip Flop Excitation Table

Present state	Next State	T
0	0	0
0	1	1
1	0	1
1	1	0

So, the above table is the excitation table for T Flip Flop.

State Table with  excitation  table

Present State			Next State			Flip Flop
Q3	Q2	Q1	Q'3	Q'2	Q'1	T3	T2	T1
0	0	0	0	0	1	0	0	1
0	0	1	0	1	0	0	1	1
0	1	0	0	1	1	0	0	1
0	1	1	1	0	0	1	1	1
1	0	0	1	0	1	0	0	1
1	0	1	1	1	0	0	1	1
1	1	0	1	1	1	0	0	1
1	1	1	0	0	0	1	1	1

Above  table is created as per follow :

When Q₃ =0 which is present state and Q₃‘=0 which is next state then T₃ become 0 [As per excitation table, have a look ]
Similarly, if Q₃ is 0 and Q₃‘ is 1 then T₃  become 1.
In similar way it goes on .

Step 3: After making the excitation table the next thing  to do is dig out the equation from the boolean algebra or K map for the design of the counter. So, for T₁ , T₂ and T₃ we got 1,  Q₁ and Q₁.Q₂

K-Map

 

For T₃ Flip flop,

 

T₃= Q₁.Q₂

For T_{2  Flip flop,}

For T₁ Flip flop,

Step 4: Lastly according to the equation got from K map create the design for 3 bit synchronous up counter.

In above design, T₁ is getting input 1 and T₂ is getting input from the output of the T₁ flip flop and lastly, T₃ is getting input from the output of T₁  and T₂ . A clock is attached to it which is in blue colour.

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SELECT DISTINCT statement 

HDLC and PPP  protocols are the communication protocol responsible for transmitting information between nodes or points. It deals data in form of frames.

Both HDLC and PPP are the part of data link layer. The major difference between them is, HDLC refers to bit-oriented protocol, whereas, PPP is byte-oriented protocol.

Difference between High-level Data Link Control Protocol and Point-To-Point protocol

High-Level Data Link Control ( HDLC )

HDLC stands for High-level Data Link Control. HDLC is a type of WAN protocol which necessarily performs the encapsulation of data inside the data link layer. This is the type of encapsulation which changes the format of data and information.

Furthermore,it is used to exchange data between nodes. It transmits data in the form of frames over a network.

It allows the use of point to point and multipoint links. It provides two types of transfer modes that is:

• Normal Response Mode (NRM): In this, station’s configuration is unbalanced. NRM involves a primary station that is capable of sending commands and multiple secondary station that can only response.
  • It can be used as point to point that includes one primary station and a secondary station that communicate with each other.
  • Other is, point to multi-point, it involves one primary station and multiple secondary stations that communicate with one other.

•  Asynchronous Balanced Mode (ABM): In this, station’s configuration is balanced. It involves only point to point communication which means single primary station and a secondary station are the part of communication. The main difference is, every station can send and receive data.

Types of frames in HDLC

It generally supports three types of frames:

•  Information frames or I frames
•  Supervisory frames or S frames
• Unnumbered frames or U frames

Frame format of HDLC

It consists 6 types of fields:

• Flag: It used to verify beginning and end of a frame. It serves synchronisation pattern for receiver
• Address: It consists address of the receiving station
• Control: It is used for error control and flow control
• Payload :Contains users data
• FCS: It stands for frame check sequence that is dedicated to error detection

Point to Point Protocol ( PPP )

PPP stands for Point-To-Point protocol. PPP is also a type of WAN protocol, which comes up with loads of advancements over the HDLC protocol. PPP protocol does not need any physical addresses or any tangible wires, only the IP address is sufficient.

It defines format of frames, connection establishment, data exchange process, Authentication process and more. However, it doesn’t support flow control, addressing mechanism and efficient error control

Frame format of PPP:

• Flag: used to verify beginning and end of a frame. It serves synchronisation pattern for receiver
• Address: It consists address of the receiving station. A constant value is used to set the address field which is 11111111 that resembles broadcast address
• Control: A constant value is used to set the field which is 11000000 . Since, flow control is not supported and PPP has very limited error control. Tberefore, it is generally not needed
• Protocol : It decides the data that is going to transmit
• Payload field :Contains users data
• FCS: It stands for frame check sequence that is dedicated to error detection

It can have two types of CPU architecture, CISC and RISC. Both provides communication between hardware and software.

These CPU architectures are capable of carrying out primary CPU tasks, though, they follow different approaches. The main difference between them is, CISC supports more instruction sets than RISC.

Difference between RISC AND CISC in Tabular Form

RISC (Reduced Instruction Set Computer)

It stands for Reduced Instruction Set Computer.

It is basically conceptualized on the fact of making hardware simpler and less complex. And this is done by implementation of the Instruction set which reduces the load on processes like loading, storing and evaluating data.

In other words, it has an assembly language that enables each and every task to be split into simpler instructions which are then executed for each clock cycle. Its instructions are efficient but due to simplicity it processes more lines of code.

It focuses on reducing execution time by optimising and simplifying instruction set. It requires only single clock cycle to process results in uniform execution time. However, it reduces efficiency in case of large program size which leads to need of more RAM for storing instruction.

RISC architecture is often used in portable devices such as mobile phones.

CISC (Complex Instruction Set Computer)

It stands for Complex Instruction Set Computer.

It is basically based on complex hardware and all the importance is given to that always. This is done by implementing complex hardware which serves as a single instruction for all the processes like loading, storing and evaluating data.

In other words, It processes larger and more complex assembly instructions each time. One CISC instruction can do the task of multiple RISC instructions.

It focuses on reducing the number of instructions per program without considering the number of cycles per instruction. It relatively requires less RAM to store instructions. It is mainly used in desktops or laptops computer.

RISC and CISC example :

Multiplying two variables X*Y:

• CISC approach can be viewed as
  MULT X, Y
• RISC approach can be viewed as
  LOAD R1, X
  LOAD R2, Y
  PROD X, Y
  STORE R3, X

Key Differences:

1. RISC machine focuses more on software and less on hardware, whereas; CISC machine focuses more on hardware and less on software.
2. RISC machine has greater use of registers so, they use transistors for more registers, whereas; CISC machine uses a greater number of complex instructions, so they use transistors to store all their complex instructions.
3. In RISC machine, as it follows a software-based approach that is why, the code part is large, whereas; in CISC machine, as it is complex hardware driven, this makes the code part much smaller.
4. In RISC machine, due to its great and reliable software approach, an instruction can execute in a single clock cycle, whereas; in CISC machine, due to its more hardware driven approach, an instruction lags a little bit and takes more than one clock cycle.
5. The RISC instructions are quite handy and easy as they can fit in a single word, whereas; the CISC instructions are quite larger than a typical word.

What is Sum of Product form?

‘Sum of Product’ is commonly abbreviated as SOP form. When an expression is expressed in a sum of binary terms ( A term refers to a set of binary variables, where each binary variable is combined with an operation) called Minterms then it is said to be Sum of Products.

In other words, An expression consisting only of minterms is called Sum of the Product. For example, A.B+A’B is an SOP expression.
[other concept Maxterm, (A+B).(A’+B’)]

SOP can be categorized into two forms :

– Canonical or Standard SOP form: In this, each and every binary variable must have in each term. For example- A.B+A’B’

– Minimal SOP form: In this, the standard SOP expression is reduced up to the minimum possible expression.

A Sum of Products question can be asked in three ways:-

1) In the form Truth table
2) In the form of non-canonical Expression
3) In the form of Boolean function

Case 1: For the given table, simplify it in SOP expression

Points

• Always consider high output (1)
• In SOP, every term in the expression is referred to as Minterm
• A Minterm is represented as m (small m)

How do you find the SOP expression from truth table?

Solution :
Step 1. Since there are 2 variables, so, therefore, there would be 2ⁿ combinations which are 2² =4.
We consider a high output as minterm. a minterm is denoted as m.
Y= m₂+m₃
Y = A.B’ +A.B                            :- It is in Canonical SOP form

In Sum of Product each term is combined with OR operation and within each term, every variable combined with AND operation.

Step 2. Now narrow the founded expression down to minimal SOP form. In this, you should know the rules of Boolean expression or K-map

Y= A.( B’ + B)
Y= A.1
Y= A

OR

Considering, A= 1, A’=0

Y= A

A is your answer.

Case 2: Simplify any expression to SOP or Sum of product form, when Boolean function is given

Simplify the following Boolean function in SOP form
F(X,Y,Z) = Σm(1,4,5,6,7)

Points to Remember

• First, check the type of m, if m is small then it would Minterm, meaning we have to solve the boolean function in respect to Sum of Product form, whereas if m is capital then it would be Maxterm, means we need to solve it in respect to Product of Sum.
• On the left side, See how many binary variables are there, in the above case there are 3 binary variables, that’s 2³ possible combinations.

How do you find the SOP expression from the boolean function?

Step 1. Make the truth table, if you want to see the actual picture or skip the step.

X	Y	Z	F
0	0	0	0 (m0)
0	0	1	1 (m1)
0	1	0	0 (m2)
0	1	1	0 (m3)
1	0	0	1 (m4)
1	0	1	1 (m5)
1	1	0	1 (m6)
1	1	1	1 (m7)

In the above table, we put output as 1 or high at the mentioned position in the above Boolean function.
For example, in Boolean function  first value is 1, so we put the output high to respective place in the truth table as output 1 at  row 001  ( represents 1)
Similarly, we have 4 , so at row 100 (represents 4)  in the truth table, we put high output.

Step 2. Now make the expression as per the above table,

F= m₁ + m₄ + m₅ + m₆ + m₇
F=  X’Y’Z + XY’Z’ + XY’Z+ XYZ’ + XYZ                :- Canonical SOP form

Step 3. Now Solve the function to minimal SOP form using K map or Boolean rules
K-map is always considered the easiest and fastest way.

 

F= X + Y’Z                   :- Minimal SOP form

This your answer

 

Case 3: Simplify any expression in SOP form, when a is given

Simplify the following expression in SOP form
F= x’z’+y’z’+yz’+xy

 OR

Simplify the following non-canonical expression in SOP form

F= x’z’+y’z’+yz’+xy

Point to remember

• Put 1 in place of missing input and convert that 1 to the appropriate Boolean rule. Suppose in above term x’z’, y is missing ( replace 1 with (y+y’))
• Make sure the expression is in Canonical form

How do you find the SOP expression from the non-canonical expression?

Step 1.   First, check the given expression is in Canonical form or not, if yes simply make K-map (or jump to 4th step ) and simplify it, otherwise follow the steps.

Step 2. Now, the above expression isn’t in canonical form as there are three binary variables or inputs, x , y and z which can’t be together found in each and every term. So to do this, make it canonical form by doing the following:-

F =  (x’.y’. 1) + (y’z’ .1) + (y z’ .1) + ( x. y.1 )

Since, in each term, a variable is missing, to bring it, in each term we have to put 1 to get the expression.

Step 3.  Put relevant input in place of 1 on the basis of Boolean rules

There is a rule, where

x + x’ =1 in Boolean algebra, we will apply it.

In the first term, y is missing  (x’y’), similarly in the second one, x is missing (y’z’) and so one.

F =  x’z'( y +y’)  +  y’z'(x+x’) + yz'(x+x’)+ xy(z+z’)
F=  x’z’y+x’z’y’+y’z’x+y’z’x’+yz’x+yz’x’+xyz+xyz’

Now, Arranging in it alphabetical order for ease of understanding

F=x’yz’+x’y’z’+xy’z’+x’y’z’+xyz’+x’yz’+xyz+xyz’

It is now in Canonical SOP or Sum of Product form

Step 3. This is the last step, shrink the expression down to minimal SOP form using K-map
or Boolean algebra

Which gives, F = z’ + xy

 

The main difference between them is, Go-Back-N protocol retransmits all the frames starting from the damaged or corrupted frame, whereas Selective Repeat protocol only retransmits frames that are damaged.

Difference between Selective Repeat and Go-Back- N sliding window protocol:

Selective Repeat sliding window protocol:

Selective repeat is one of the sliding window protocols which is essentially responsible for detecting and correcting the error caused in the data link layer.

The Selective repeat protocol basically only retransmits the damaged or lost frame.

The retransmitted frame in the selective repeat protocol is always received out of sequence.

Go-back-N sliding window protocol:

Go-back-N is also one of the sliding window protocols. This protocol mechanism is essentially used to control and detect the errors occurring in the data link layer.

During the data transmission between the sender and the receiver; if the acknowledgement is lost or the frame has been damaged then the sender has to resend all the frames starting from the damaged or corrupted frame.

The main difference between them is, OSI reference model provides clear distinction between services,interface and protocols, whereas, TCP/IP doesn’t able to differentiate between them.

Difference between TCP/IP And OSI Reference Model in Tabular form

TCP/IP Model

TCP/IP model is older than OSI model and consists 4 layer initially ,later on one more layer were added.

It defines standardised rules that enables network communication between computer as the internet.

These are the layers :-

• Application Layer

It corresponds to Application, Presentation and Session Layer of OSI Model. It contains all the high-level protocols. It provides various services to perform user activities ranging from file transfer to internet surfing.

It consists of HTTP, SMTP, FTP protocols and more.

• Transport Layer

It ensures reliable transmission of data that is sent between hosts in the form of datagrams. It supports flow control and error control to make sure data is received at destination host reliably and correctly.

TCP(Transmission Control Protocol) and UDP(User Datagram Protocol) are protocols used in this layer.

• Internet Layer

It is responsible for transmitting data packets between hosts on a network. It routes independent data packets to correct host. It uses IP(Internet Protocol), ICMP (Internet Control Message Protocol) and ARP ( Address Resolution) protocol to achieve its function.

• Link Layer

It is a combination of the Data Link layer and Physical layer of OSI Model. It acts as an interface between transmission links and hosts. It uses a physical address to find hosts and send data.

OSI Reference Model

OSI Model stands for Open System Interconnection reference model which was developed by ISO. It facilitates open communication systems to communicate using Standard Protocols.

It is not a network architecture as it only states what a layer should do, but not describes the exact services and protocol to be used in each layer.

It follows certain principles on the basis of which it came to the decision of having 7 layers. Each and every layer has its own separate functionality.

These are the following 7 layers in OSI model :-

• Application Layer

It is the only layer that communicates with users for data directly. Network applications such as Skype, Chrome and other applications work in this layer.

They use application layer protocols such as HTTP, SMTP, FTP, POP3 to function. Application layer provides various services to perform user activities ranging from file transfer to internet surfing.

• Presentation Layer

It accepts data from the application layer in the form of a sequence of numbers or characters and transforms it into a machine-understandable form which is binary data (10101010).

After that, data compression is used to reduce the size of the data before handing it over to the next layer. It accelerates the data transmission speed and therefore, it helps in case of video calls.

Lastly, data encryption is used to encrypt data in order to maximise the integrity and security. It secures the transmitting data from intruders.

SSL protocol is one of the protocols used in this layer

Objective Highlights

• • Data Translation
  • Data Compression
  • Data Encryption

• Session layers

It establishes, maintains, manages, and terminates connection or sessions between hosts. It uses various APIs (Application Programming Interface) to connect computers.

When a client requests for connection setup, the server uses authentication and authorisation before allowing the client to use its resources. Authentication can be defined as a process of identifying a user.

The authorisation is a process of identifying the access rights of a user, deciding what resources are allowed to access. Session layer also keeps track of which data packets belong to which file.

Objective Highlights

• • Session Establishment
  • Session Management
  • Session Termination

• Transport Layer

It ensures communication reliability by performing segmentation, error control and flow control.

It accepts data from the session layer and divides it into various segments and each segment consists of the information of the source, destination port number and sequence number. This is known as segmentation.

Port number is used to deliver the data to correct application, whereas the sequence number is used to put the data into the correct sequence.

Further, flow control handles the amount or size of data to be transmitted. Error control comes handy when a data packets are dropped in between transmission & not reached to the destination, then using various techniques, it retransmits data again. It also uses a checksum to identify the received corrupted segment.

TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) are the protocols used in this layer.

Objective Highlights

• • Data Segmentation
  • Error Control
  • Flow Control

• Network Layer

This layer is responsible for transmitting received data segments from source host to destination host over a network.

It performs functions like logical addressing, routing and path determination. In this, each data unit is referred as data packets.

IP addressing done in this layer is called logical addressing. Each computer has an IP address to get uniquely identified on a network.

It assigns sender’s and receiver’s address to each segment, so, that they can reach at correct destination. Furthermore,
routing is also used to find an efficient and effective path from source to destination.

Lastly, path determination can be defined as a technique to select the best path for data delivery. OSPF, BGP, IS-IS are some protocols used in this layer.

Objective Highlights

• • Logical Addressing
  • Routing
  • Path Determination
• Data Link Layer

It accepts data from the network layer. It performs physical addressing that is used to assign MAC address of sender and receiver host to received data packets to form a frame.

It also ensures the data transmission from one node to other must be error-free. It also takes care of the problem of controlling access to the shared channel using a sublayer called medium access control.

• Physical Layer

It converts data received from the data link layer to bitstream and is responsible for actual connectivity between the devices.

It involves physical equipment ranging from cables to switches for data transfer.

The main difference between them is, Modem connects your computer with the internet whereas, router directs and examines data packets to destination devices.

Difference between Modem and Router in tabular form ?

Modem

It is used to connect a computer to internet. It establishes and maintains a dedicated internet connection with Internet Service Provider (ISP) that serves access to Internet.

The reason to have modem is because a computer can only deal with digital signals whereas signals present on internet are analog.

A modem demodulates incoming analog signals from internet to digital signal.

Similarly, a modem modulates the outgoing signals, coming from computer to analog signals. Cable and DSL modem are some examples.

A Modem stands for Modulator and DEModulator.

The main objective of the Modem is to convert digital signals to analog signals while transmitting and converting back analog signals to digital signals while receiving data.

Router

A Router can be defined as a networking device that is basically used to carry forward the data packets to various computer networks.

Routers are used while transmitting data so that they can efficiently direct the Internet traffic.

In other words, It routes a dedicated internet connection to various devices such as laptops, computers, mobile phones and others, so that, they can access the internet.

It comes up with multiple ports which can be used to connect devices using Ethernet cables, along with that, it also provides wireless points.

Key Differences:

1. Layer (in which it resides):

Modem resides in DATA LINK LAYER whereas, Router resides in NETWORK LAYER.

2. Form of data transmission:

In both the modem as well as routers, the data is transmitted in the form of PACKETS.

3. Device type:

A modem is an INTER-NETWORKING device whereas, a router is a NETWORKING device.

4. Ports:

Modem:    2 PORTS-

• One for ISP connection.
• Second for connecting to the router.

Router:     Can have MULTIPLE PORTS.

5. Security:

A Modem does not provide any kind of security whereas; Router provides security by protecting the network.

The communication that first requires establishing a proper connection before sending actual data is called as Connection-oriented communication.

This connection-oriented communication is similar to the telephone system.

CONNECTION-LESS COMMUNICATION:

The communication in which the actual packets of data are directly sent/transmitted from source to destination without establishing a connection first is called Connection-less communication.

This connection-less communication is quite similar to the postal system.

DIFFERENCE BETWEEN CONNECTION-ORIENTED AND CONNECTION-LESS COMMUNICATION:

1. Connection-oriented communication always guarantees a proper and reliable transfer of data. Connection-less communication can never guarantee a proper transfer of the data.

2. In Connection-oriented communication, there is no chance of any kind of congestion or obstructions what so ever while transferring the data. In Connection-less communication there is a greater chance and more often observed that there is congestion or any obstruction while transferring the data.

3. The virtual circuit and circuit switching are commonly used to implement Connection-oriented communication. The packet switching is commonly used to implement Connection-less communication.

4. DATA RE-TRANSMISSION( IN CASE OF DATA LOSS)-

In Connection-oriented communication, if the data is lost then the retransmission can be done and is very easily feasible. In Connection-less communication, if the data is lost then retransmission is not possible and feasible at all.

5. The Connection-oriented communication is most commonly used for steady and prolonged communication. The Connection-less communication is most commonly used for short distance communication.

6. In Connection-oriented communication, there is a need for firstly establishing a prior connection before the actual transmission could take place. In Connection-less communication there is no requirement of establishing any kind of prior connection before transmitting the data.

Key differences: