Explain Two-dimensional Parity check.

Question: What do you mean by error detecting codes? Explain Two-dimensional Parity check. 

Answer 

Error: 

A condition when the receiver’s information does not match with the sender’s information.
During transmission, digital signals suffer from noise that can introduce errors in the binary
bits travelling from sender to receiver. That means a 0 bit may change to 1 or a 1 bit may change to 0.

Error Detecting Codes (Implemented either at Data link layer or Transport Layer of OSI Model)

Whenever a message is transmitted, it may get scrambled by noise or data may get corrupted.
To avoid this, we use error-detecting codes which are additional data added to a given digital
message to help us detect if any error has occurred during transmission of the message.

Basic approach used for error detection is the use of redundancy bits, where additional bits
are added to facilitate detection of errors.

Some popular techniques for error detection are:

1. Simple Parity check

2. Two-dimensional Parity check

3. Checksum

4. Cyclic redundancy check

Two-dimensional Parity check

Parity check bits are calculated for each row, which is equivalent to a simple parity check bit.
Parity check bits are also calculated for all columns, then both are sent along with the data.
At the receiving end these are compared with the parity bits calculated on the received data.

What do you mean by error detecting codes? Explain Simple Parity Check with example.

Question: What do you mean by error detecting codes? Explain Simple Parity Check
with example. 

Answer 

Error: 

A condition when the receiver’s information does not match with the sender’s information.
During transmission, digital signals suffer from noise that can introduce errors in the binary bits
travelling from sender to receiver. That means a 0 bit may change to 1 or a 1 bit may change
to 0.

Error Detecting Codes (Implemented either at Data link layer or Transport Layer of OSI Model)

Whenever a message is transmitted, it may get scrambled by noise or data may get corrupted.
To avoid this, we use error-detecting codes which are additional data added to a given digital
message to help us detect if any error has occurred during transmission of the message.

Basic approach used for error detection is the use of redundancy bits, where additional bits
are added to facilitate detection of errors.

Some popular techniques for error detection are:

1. Simple Parity check

2. Two-dimensional Parity check

3. Checksum

4. Cyclic redundancy check

Simple Parity check

Blocks of data from the source are subjected to a check bit or parity bit generator form,
where a parity of :

• 1 is added to the block if it contains odd number of 1’s, and
• 0 is added if it contains even number of 1’s

This scheme makes the total number of 1’s even, that is why it is called even parity checking.

Explain CRC with Example.

CRC Example 

• In CRC, a sequence of redundant bits, called cyclic redundancy check bits, are appended to the end of data unit so that the resulting data unit becomes exactly divisible by a second, predetermined binary number.
• At the destination, the incoming data unit is divided by the same number. If at this step there is no remainder, the data unit is assumed to be correct and is therefore accepted.
• A remainder indicates that the data unit has been damaged in transit and therefore must be rejected.

Explain Types of Error with example.

Question: Explain Types of Error with example. 

Answer 

There are many reasons such as noise, cross-talk etc., which may help data to get corrupted
during transmission. Most of the applications would not function expectedly if they receive
erroneous data. Applications such as voice and video may not be that affected and with some
errors they may still function well.

Types of Errors

There may be three types of errors:

• Single bit error
  
  In a frame, there is only one bit, anywhere though, which is corrupt.
• Multiple bits error
  
  Frame is received with more than one bits in corrupted state.
• Burst error
  
  Frame contains more than1 consecutive bits corrupted.

Question: Explain DHCP in detail.

Question: Question: Explain DHCP in detail. 

Answer 

The DHCP protocol gives the network administrator a method to configure the network from a
centralised area. With the help of DHCP, easy handling of new users and reuse of IP addresses
can be achieved.

DHCP is a network protocol that is used to assign various network parameters to a device.
This greatly simplifies administration of a network, since there is no need to assign static
network parameters for each device.

DHCP is a client-server protocol. A client is a device that is configured to use DHCP to
request network parameters from a DHCP server. DHCP server maintains a pool of available
IP addresses and assigned one of them to the host. A DHCP server can also provide some
other parameters, such as:

• subnet mask
• default gateway
• domain name
• DNS server

Cisco routers can be configured as both DHCP client and DHCP server.

DHCP process explained:

DHCP client goes through the four step process:

DHCP port number for server is 67 and for the client is 68. It is a Client server protocol which
uses UDP services

1: A DHCP client sends a broadcast packet (DHCP Discover) to discover DHCP servers on the
LAN segment.

2: The DHCP servers receive the DHCP Discover packet and respond with DHCP Offer packets,
offering IP addressing information.

3: If the client receives the DHCP Offer packets from multiple DHCP servers, the first DHCP
Offer packet is accepted. The client responds by broadcasting a DHCP Request packet,
requesting the network parameters from the server that responded first.

4: The DHCP server approves the lease with a DHCP Acknowledgement packet. The packet
includes the lease duration and other configuration information.

Advantages – The advantages of using DHCP include:

• centralized management of IP addresses
• ease of adding new clients to a network
• reuse of IP addresses reducing the total number of IP addresses that are required
• simple reconfiguration of the IP address space on the DHCP server without needing to

  reconfigure each client

Disadvantages – Disadvantage of using DHCP is:

• IP conflict can occur

Explain ARP with an example.

Question: Explain ARP with an example.

Answer 

ARP (Address Resolution Protocol) is a network protocol used to find out the hardware
(MAC) address of a device from an IP address. It is used when a device wants to
communicate with some other device on a local network (for example on an Ethernet
network that requires physical addresses to be known before sending packets). The sending
device uses ARP to translate IP addresses to MAC addresses. The device sends an ARP
request message containing the IP address of the receiving device. All devices on a local
network segment see the message, but only the device that has that IP address responds
with the ARP reply message containing its MAC address. The sending device now has
enough information to send the packet to the receiving device.

ARP request packets are sent to the broadcast addresses (FF:FF:FF:FF:FF:FF for the
Ethernet broadcasts and 255.255.255.255 for the IP broadcast).

Here is the explanation of the ARP process:

Let’s say that Host A wants to communicate with host B. Host A knows the IP address of host
B, but it doesn’t know the host B’s MAC address. In order to find out the MAC address of host
B, host A sends an ARP request, listing the host B’s IP address as the destination IP address
and the MAC address of FF:FF:FF:FF:FF:FF (Ethernet broadcast). Switch will forward the
frame out all interfaces (except the incoming interface). Each device on the segment will
receive the packet, but because the destination IP address is host B’s IP address, only host
B will reply with the ARP reply packet, listing its MAC address. Host A now has enough
information to send the traffic to host B.

All operating systems maintain ARP caches that are checked before sending an ARP request
message. Each time a host needs to send a packet to another host on the LAN, it first checks
its ARP cache for the correct IP address and matching MAC address. The addresses will stay
in the cache for a couple of minutes. 

You can display ARP entries in Windows by using the arp -a command.

What is constellation diagram? Draw constellation diagram for ASK, BPSK, QPSK.

Question : What is constellation diagram? Draw constellation diagram for ASK,
BPSK, QPSK.

Ans:   

Constellation diagrams are 2D graphical representations of digitally modulated signals.

A constellation diagram can help us define the amplitude and phase of a signal element,
particularly when we are using two carriers (one in-phase and one quadrature).

The diagram is useful when we are dealing with multilevel ASK, PSK, or QAM (see next

section). 

In a constellation diagram, a signal element type is represented as a dot. The bit or combination
of bits it can carry is often written next to it.

The diagram has two axes. The horizontal X axis is related to the in-phase carrier; the vertical
Y axis is related to the quadrature carrier. 

For each point on the diagram, four pieces of information can be deduced. 

The projection of a point on the X axis defines the peak amplitude of the in-phase
component; the projection of a point on the Y axis defines the peak amplitude of the
quadrature component. 

The length of the line (vector) that connects the point to the origin is the peak amplitude
of the signal element (combination of the X and Y components); 

The angle the line makes with the X axis is the phase of the signal element.

For ASK, we are using only an in-phase carrier. Therefore, the two points should be on the X axis.

Binary 0 has an amplitude of 0 V; binary 1 has an amplitude of 1 V. 

BPSK also uses only an in-phase carrier.

BPSK creates two different signal elements, one with amplitude 1 V and in phase and the other
with amplitude 1 V and 180° out of phase.

QPSK uses two carriers, one in-phase and quadrature.

11 is represented by (1,1) and phase of 45

01 is represented by (-1,1) and phase of 135

00 is represented by (-1,-1) and phase of -135

10 is represented by (1,-1) and phase of -45

The same way QAM can be represented by  different values as mentioned below. 

What do you mean by sub netting? Explain with one example.

Question : What do you mean by subnetting? Explain with one example.

Ans:   

A subnetwork or subnet is a logical subdivision of an IP network. The practice of dividing a network into two or more networks is called subnetting.

Advantages of Subnetting: 

1. Improve network performance and speed:

A single broadcast packet sends out information that reaches every device connected to that network. 

Subnetting enables you to ensure that the information remains in the subnetted network or broadcast domain, which allows other subnets to maximize their speed and effectiveness.

2. Reduce network congestion:

Every computer would see broadcast packets from all the computers and servers on the network. This leads to increased congestion, reduced network performance, and slower response times.

Subnetting ensures that traffic destined for a device within a subnet stays in that subnet, which reduces congestion. 

3. Increasing the network security:

By splitting your network into subnets, you can control the flow of traffic using ACLs, QoS, or route-maps, enabling you to identify threats, close points of entry, and target your responses more easily.

Another option is to limit access to resources on wireless clients, ensuring that valuable information isn’t easily accessible in remote locations.

4. Control network growth:

Without subnetting there is a waste of thousands of IP Address. Subnetting allows you to create group as per your requirement. You can be more sure about the perfect utilization of all available hosts in your network.

5. Easy administration:

By subnetting, you can create networks as per your requirements. You can control easily all this logical group of networks. With careful planning and implementation, subnetted networks generally are easier to manage and troubleshoot.

Example of Subnetting: 

Divide the network 193.1.2.0 network with 2 subnetwork.

First thing, It is a class C IP so, there are 24 bits in the network id part and 8 bits in the host id part.

To divide a network into two ( 21=2 ) parts you need to choose one bit from host id part for each subnet i.e, (0,1).

For Subnet-1:

The first bit which is chosen from the subnetting bit  id part is zero.

So now range will:  193.1.2.00000000      (host all zero)

                                      193.1.2.01111111      (host all one)

Thus, the range of subnet-1: 193.1.2.0 to 193.1.2.127

For Subnet-2:

The first bit chosen from the subnetting bit id part is one.

So now range will: 193.1.2.100000000 

                                     193.1.2.11111111

Thus, the range of subnet-2: 193.1.2.128 to 193.1.2.255

And the subnet mask will be : 255.255.255.1000 0000        (subnetting bit 1 is added)

                                                          255.255.255.128

Kindly note that here in the subnet range first IP will be considered as a network IP address and last IP of that subnet range will be considered as a broadcast IP address.