Computer Networks | Subject Wise

Given
SAN switch have Number of ports = 24 ports
Channel capacity of each port = 8Gbps
Aggregate Bandwidth = Number of ports * Channel capacity of each port.
Aggregate Bandwidth = 24 * 8 = 192 Gbps

Bandwidth = 2.048 Mbps
Error bits = 512
Bit error rate is the number of bits sent per data in 10 hours , we sent 512 bit error
10 hours  = 512 bit error
36000 secs = 512 bit error
1 sec      = 512/36000
1 sec      = 0.0142 bit error.

Error rate = Total number of error bits / Bandwidth

Error rate =   (0.0142)/(2.048 x 10⁶)
Error rate = 6.944 x 10^-9

• The Lightweight Directory Access Protocol (LDAP) is an open, vendor-neutral, industry standard application protocol for accessing and maintaining distributed directory information services over an Internet Protocol (IP) network
• A common use of LDAP is to provide a central place to store usernames and passwords. This allows many different applications and services to connect to the LDAP server to validate users
• When an LDAP session is created, that is, when an LDAP client connects to the server, the authentication state of the session is set to anonymous. The BIND(authenticate) operation establishes the authentication state for a session.
• LDAP is often used by other services for authentication and/or authorization (what actions a given already-authenticated user can do on what service)

In synchronous mode of transfer we don’t require start and stop bits

• Total number of bits per character while transmitting is (7+1)=8 bits
• Bandwidth = 19.2 kbps
• Number of character transmitted in 1 second = (19.2 *1000)/8 = 2400

In Asynchronous transfer, we need start and stop bits in order to synchronize these bits are added to the number of bits in each character.

• Total number of bits per character while transmitting is (7 data bit + 1 parity bit + 1 start bit + 1 stop bit)=10 bits
• Bandwidth = 19.2 kbps
• Number of character transmitted in 1 second = (19.2 *1000)/10 = 1920

• IEEE 1394 is an interface standard for a serial bus for high-speed communications and isochronous real-time data transfer.
• It was developed in the late 1980s and early 1990s by Apple, which called it FireWire,
• FireWire is also available in Cat 5 and optical fiber versions.
• The 1394 interface is comparable to USB.
• USB was developed subsequently and gained much greater market share. USB requires a master controller whereas IEEE 1394 is cooperatively managed by the connected devices.

Refer : https://en.wikipedia.org/wiki/IEEE_1394

• The first field(Preamble) of 802.3 frame contains 7 bytes of alternating 0's and 1's that alerts the receiving system to the coming frame and enables it to synchronize its input timing
• Preamble belongs to the physical layer and are added at the physical layer only and is not part of the frame.

Switch act as a collision domain separator not not as a broadcast domain separator.

• Switch is a collision domain separator because it has lookup table associated with it
• Each lookup table entry contains a port associated with the switch and the MAC address of the concerned device(computer) associated with this port.
• Hence collisions domain is separate for each switch.
• Switch is nothing but an active hub.
• Switch is not a broadcast domain separator . But it can be made so using the concept of virtual switching.
• So in that case it will be a broadcast domain separator

T_t(data) : Transmission delay for Data packet
T_p(data) : propagation delay for Data packet

T_t = 20 ns.
T_p = 30 ns

Efficiency of stop and wait protocol =  [ 1 / (1 + 2a) ]

Where  a = T_p / T_t
T_p = propagation delay
T_t = transmission delay

Efficiency = 1 / (1 + 2(30/20))
Efficiency = 1/4 * 100
Efficiency = 25 %
option(B) is correct Answer

IPv6 support the following Addressing Modes:

• Unicast addressing : In unicast mode of addressing, an IPv6 interface (host) is uniquely identified in a network segment. A packet is delivered to one interface
• Multicast addressing : IPv6 supports multicast features as the single packet data can be sent to multiple destination hosts at a time.
• Anycast addressing :  A packet is delivered to the nearest of multiple interfaces. Multiple interfaces (hosts) are assigned same Anycast IP address.

Broadcast addressing is not supported by IPV6.

subnet mask is 255.224.0.0
Equivalent Binary representation will be

• 255 = 11111111
• 224 = 11100000
• 0      = 00000000
• 0      = 00000000

Subnet mask = 11111111.11100000.00000000.00000000

• First 8 1's Represent Class A
• Next 3 1's used for subnet.

Number of subnets possible with 3 bits = 2³=8 

• Leaky bucket algorithm is used to control transmission rate in a network.
• Leaky bucket algorithm is used to check data transmissions, in the form of packets to define limits on bandwidth.
• By setting the bucket size and output flow rate, the code can be refined to slow, medium and fast.
• It is implemented as a single-server queue with constant service time.
• If the bucket (buffer) overflows then packets are discarded.
• In this algorithm the input rate can vary but the output rate remains constant.
• Algorithm saves busty traffic into fixed rate traffic by averaging the data rate.

• Packet filtering firewalls operate at the network layer (Layer 3) of the OSI model.
• Packet filtering firewalls make processing decisions based on network addresses, ports, or protocols
• Packet filtering firewalls examine the packet headers that contain IP addresses and packet options and block or allow traffic through the firewall based on that information

The Protocol Data Unit is the unit of communication at a particular layer.

• Physical Layer PDU is the bit or, more generally, symbol
• Data Link Layer PDU is the frame.
• Network Layer PDU is the datagram.
• Transport Layer The transport layer PDU is  segment for TCP
• Application Layer PDU is the data or message.
• link layer PDU is the frame.

A layer lower in the Internet protocol suite, at the Internet layer, the PDU is called a packet, irrespective of its payload type.

For detecting d bit error, we need d+1 bits
Here d=2 So We require = 3 bits
For correcting d bit error we need 2d+1 bits
Here, d=1 bits So we require = 2 * 1 + 1 = 3 bits
∴ Total bits = 3 + 3 = 6

Port Address Translation (PAT) is an extension to network address translation (NAT) that permits multiple devices on a local area network (LAN) to be mapped to a single public IP address. The goal of PAT is to conserve IP addresses.

Network address translation (NAT)  designed for IP address conservation. Network address translation (NAT) is the process of modifying IP address information in IP packet headers while in transit across a traffic routing device. NAT operates on a router, usually connecting two networks together, and translates the private (not globally unique) addresses in the internal network into legal addresses, before packets are forwarded to another network

Address mapping (also know as pin mapping or geocoding) is the process of assigning map coordinate locations to addresses in a database. The output of address mapping is a point layer attributed with all of the data from the input database.

Port mapping or port forwarding is an application of network address translation (NAT) which redirects a communication request from one address and port number combination to another while the packets are traversing a network gateway, such as a router or firewall.

• Open Shortest Path First (OSPF) is a routing protocol for Internet Protocol (IP) networks.
• It uses a link state routing (LSR) algorithm to calculate the shortest route to a destination through a network based on an algorithm
• Routing Information Protocol (RIP) and Open Shortest Path First (OSPF) are Interior Gateway Protocol, i.e., they both are used within an autonomous system.
• RIP is an old protocol (not used anymore) based on distance vector routing.
• OSPF is based on Link State Routing.

Basic RSA Algorithm:
1. Choose two primes, p and q.
2. Compute n=p*q and z=(p-1)*(q-1).
3. Choose a number relatively prime to z and call it d.
4. Find e such that e*d=1 mod z.

Given two distinct prime numbers p = 5 and q = 11 and  encryption key, e = 27
Compute n = p * q = 5 * 11 = 55
Calculate the totient z = (p-1) * (q-1) = 4 * 10 = 40

Let the value of decryption key be ‘d’ such that :

e * d mod z = 1
27 * d mod 40 = 1
d = 3

Value of decryption key be  d = 3

HLEN = 5
Header length = 5 * 4 = 20 bytes
Total length field = 200
So payload size = 200 – 20 = 180
Starting number of first byte of fragment=100*8=800
Therefore, number of last byte in packet = 800 + 180 – 1 = 979

Given data
Bandwidth =50 kbps
Frame size = 1000 bits

Round trip time = 2 * Propagation time  = Propagation time =500/2= 250 ms
( A ----> satellite -----> B ) + ( B----> satellite --->A )  = 500 ms
A ---> satellite ----> B   equal to B ---->satellite ---->A  = 250ms

Transmission time = Message size / bandwidth  = 1000 bits / 50 kbps = 20 ms

Time to receive the frame by the receiver  = 250 + 20 = 270 ms

IP Packet header length = 20B to 60B
It is given in the question that Arrived Packet has 8 bits = 0100 0010
First 4 Bits  0100 Represents Version  = IPV₄
Next 4 Bits Represents Header Length ( /4) which is range between 20 to 60 bytes.

0010 represents header length  which  is equal to 2 * 4 = 8B
But header length between  20B to 60B

So Receiver will reject the packet because 8B < 20B it should between 20B ≤ x ≤ 60B

• For a browser to connect and access the web servers HTTP is used and HTTP works on a well defined port number 80.
• TCP is Underlying protocol of HTTP
• TCP is protocol at Transport Layer
• Transport layer which is responsible for creating the end to end Connection between hosts for which it mainly uses TCP and UDP.
• TCP is a secure and connection orientated protocol which uses a handshake protocol to establish a robust connection between two end hosts.
• TCP ensures reliable delivery of messages and is used in various applications.
• UDP  is a stateless and unreliable protocol which ensures best-effort delivery. It is suitable for the applications which have little concern with flow or error control and requires to send the bulk of data like video conferencing.

• Auto negotiation is a signaling mechanism and procedure used by Ethernet over twisted pair by which two connected devices choose common transmission parameters, such as speed, duplex mode, and flow control.
• Auto negotiation is defined in clause 28 of IEEE 802.3 and was originally a component of Fast Ethernet.

• Unicast: from one source to one destination. It means  unicast is One-to-One
• Broadcast: from one source to all possible destinations. It means Broadcast is One-to-All
• Multicast: from one source to multiple destinations stating an interest in receiving the traffic. It means Multicast is One-to-Many. A multicast addressed frame is either flooded out all ports (if no multicast optimization is configured) or sent out only the ports interested in receiving the traffic.
  Multicast MAC Address range of 01-00-5E-00-00-00 to 01-00-5E-7F-FF-FF

The broadcast address has the value of FFFF.FFFF.FFFF (all binary ones). The switch will flood broadcast frames out all ports except the port that it was received on.

Multicast frames have a value of 1 in the least-significant bit of the first octet of the destination address. This helps a network switch to distinguish between unicast and multicast addresses. One example of an Ethernet multicast address would be 01:00:0C:CC:CC:CC, which is an address used by CDP (Cisco Discovery Protocol).

130.34.12.64/26
2^32-26 = 2⁶ = So 64 hosts are possible.

IP Address      130.34.12 .0100 0000
Subnet Mask  255.255.255 .1100 0000

Dividing it into four subnets will give 16 per subnet

• 130.34.12.64 to 130.34.12.79
• 130.34.12.80 to 130.34.12.95
• 130.34.12.96 to 132.34.12.111
• 130.34.12.112 to 130.34.12.127

• Perform AND operation between the supernet Mask and the given IP addresses
• Result of the above AND operation matches with the first address of the supernet then given IP address is in the same supernet.

So above result is matching with first address of the supernet So given IP address is in the same supernet.

For Pure aloha Throughput  (S) = Ge^-2G.
For Slotted aloha Throughput  (S) = Ge^-G.

Given Time Period  = 100 ms
we know that Frequency is the inverse of Time Period.
Frequency = ( 1 / Time Period )
Frequency = 1 / 100ms
Frequency = 1/10^-1s   // 100*10^-3s = 10^-1s
Frequency = 10Hz  // 1 Hz = 10^-3 kHz
Frequency =10^-2KHz  // 10 * 10^-3 kHz  = 10^-2KHz

Given IPV4 address
10000001 00001011 00001011 11101111
(10000001)₂ = 2⁷+2⁰=(129)₁₀
(00001011)₂  = 2⁰+2³+2¹=(11)₁₀
(00001011)₂  = 2⁰+2³+2¹=(11)₁₀
(11101111)₂   = 2⁰+2¹+2²+2³+2⁵+2⁶+2⁷=(239)₁₀
Given IPV4 address which  is equivalent to 129.11.11.239

• option(A) : False
  The first generation (1G) of cellular mobile communication systems, called Advanced Mobile Phone System (AMPS) in North America, used analog FM in 30 kHz channels and accommodated multiple users through frequency division multiple access in the 800–900 MHz band allocated by the 1976 World Allocation Radio Conference
• option(B) : True IS – 95 is a second generation cellular phone system based on CDMA and DSSS.
• option(C) : True The Third generation cellular phone system will provide universal personnel communication.

DES: Data Encryption Standard)
DES(Data Encryption Standard) is an implementation of a Feistel Cipher. It uses 16 round Feistel structure. The block size is 64-bit. Though, key length is 64-bit, DES has an effective key length of 56 bits, since 8 of the 64 bits of the key are not used by the encryption algorithm (function as check bits only).

IDEA: International Data Encryption Algorithm (IDEA)
DEA operates on 64-bit blocks using a 128-bit key

BLOW FISH:  Blowfish Cryptosystem
BLOW FISH is the replacement for DES or IDEA,
64-bit block cipher with variable length key. The key length is variable ,
it can be in the range of 32~448 bits
Default 128 bits key length

AES: Advanced Encryption Standard
AES is based on is a symmetric key algorithm it means the same key is used for both encrypting and decrypting the data.
Advanced Encryption Standard (AES) uses block size 128 and key sizes 128, 192, 256

• Blowfish, AES, RC4, DES, RC5, and RC6 are examples of symmetric encryption. The most widely used symmetric algorithm is AES-128, AES-192, and AES-256.
• Asymmetric encryption Example are EIGamal , RSA, DSA, Elliptic curve techniques, PKCS, Diffie-Hellman, ECC,

option(A) : True
Three broad categories of Networks are
(i) Circuit Switched Networks
(ii) Packet Switched Networks
(iii) Message Switched Networks

option(B) : False
In Circuit Switched the Network resources need to be reserved during the setup phase; the resources remain dedicated for the entire duration of data transfer phase until the teardown phase.

option(C) : True
In Packet switching, there is no resource allocation for a packet. This means that there is no reserved bandwidth on the links, and there is no scheduled processing time for each packet. Resources are allocated on demand.

The shift cipher is sometimes referred to as the Caesar cipher.

In Caeser cipher algorithm encryption and decryption takes place. During encryption right shift takes place depending upon the key  and in  Decryption left shift takes place depending on key.

The message "WTAAD" is already encrypted. we need to decrypt it by simply shifting the keys by 15 places in reverse order.

Decryption
Use the shift cipher with key = 15 to decrypt the message “WTAAD.”

• We decrypt one character at a time.
• Each character is shifted 15 characters  up.
• Letter W is decrypted to H.
• Letter T is decrypted to E.
• The first A is decrypted to L.
• The second A is  decrypted to L.
• Finally D is decrypted to O.
• The plaintext is HELLO

Encryption
Use the shift cipher with key = 15 to encrypt the message “HELLO.”

• We encrypt one character at a time.
• Each character is shifted 15 characters characters down.
• Letter H is encrypted encrypted to W.
• Letter E is encrypted to T.
• The first L is encrypted to A.
• The second L is also encrypted encrypted to A.
• O is encrypted encrypted to D.
• The cipher text is WTAAD.

In question encryption of given message using Transposition Cipher with Given message is “HELLO MY DEARZ”
Key - Plain Text -> 2 4 1 3
Key - Cipher Text -> 1 2 3 4

According to key size divide number of character into blocks. Here, key size is 4. So, character block size is 4.

Step 1 : Given message is “HELLO MY DEARZ”  Now arrange them in group of 4
I.e. HELL OMYD EARZ
Step-2: Sort column as per given Plain key as shown in below matrix.
i.e. replace second character in above format to the first place and
fourth character to the first place ,
first character to the third place
third character to the fourth place.
Encrypted message will be :  ELHL MDOY AZER.
Read the matrix horizontally one by one row

• TTL field is used to limit the lifetime of a IP datagram and to prevent indefinite looping of IP datagrams.
• TTL may be implemented as a counter or timestamp attached to or embedded in the data.
• Once the prescribed event count or timespan has elapsed, data is discarded.

Direct Broadcast Address is represented as valid Network ID + all hosts bits will be 1's ( series of 1's )

201.15.16.31 = 201.15.00010000.00011111

last 5 bits are the host bits

Last octet of given DBA is 0001 1111.

So, in Subnet mask address all should be 1’s except last 5 digits, i.e., 27 bit for NID which is 255.255.255.224

So none of the options is correct

Given Time Period  = 100 ms
we know that Frequency is the inverse of Time Period.
Frequency = ( 1 / Time Period )
Frequency = 1 / 100ms
Frequency = 1/10^-1s   // 100*10^-3s = 10^-1s
Frequency = 10Hz  // 1 Hz = 10^-3 kHz
Frequency =10^-2KHz  // 10 * 10^-3 kHz  = 10^-2KHz

• HTTP may use different TCP connection for different objects of a webpage if non-persistent connections are used.
• FTP uses data and control connections used with two separate TCP connections
• TELNET and FTP can only use ONE connection at a time

Email uses various protocols like SMTP, IMAP and POP. The most prominent one used in application layer is SMTP

• TCP and UDP are two transport layer protocols. SMTP uses TCP as transport layer protocol as TCP is reliable.
• Since TCP is a reliable protocol, it’s more efficient to use TCP protocol for e-mail transfer. TCP also provides more security than other transport layer protocols.

Why TCP not UDP?
SMTP makes more sense to use TCP over UDP. SMTP is a mail transport protocol, and in mail every single packet is important. If you lose several packets in the middle of the message the recipient might not even receive the message and if they do they might be missing key information. This makes TCP more appropriate because it ensures that every packet is delivered.

The Internet Assigned Numbers Authority (IANA) reserves the following IP address blocks for use as private IP addresses:

• 10.0.0.0/8          IP addresses:  10.0.0.0 – 10.255.255.255
• 172.16.0.0/12     IP addresses:  172.16.0.0 – 172.31.255.255
• 192.168.0.0/16  IP addresses: 192.168.0.0 – 192.168.255.255

option(A) and option(D) are not valid IP's  because it is beyond 255. IP address ranges from [0 - 255]

option(B) is private IP address

only option(C) is correct

Message M = 1010001101
Divisor polynomial = x⁵ + x⁴ + x² +1
Divisor polynomial = 1.x⁵ +1.x⁴+0.x³+1.x²+0.x¹+1.x⁰
Divisor polynomial bit= 110101
Bits to be appended to message M= (divisor polynomial bits – 1) = 5
So, Append 5 zeros to message bits M
Modified Message M = 101000110100000

Now perform EX-OR between message M and  divisor polynomial bits.

So now add remainder to the original Message M
∴ M'= 101000110101110 and CRC = 01110.

A multipoint communication is established when three or many network nodes are connected to each other. Frame relay, Ethernet, token ring and ATM are some examples of multipoint connections.

• Bits per second is straightforward. It is exactly what it sounds like. If I have 1000 bits and am sending them at 1000 bps, it will take exactly one second to transmit them.
• Baud is symbols per second. If these symbols — the indivisible elements of your data encoding — are not bits, the baud rate will be lower than the bit rate by the factor of bits per symbol.

Refer : https://stackoverflow.com/questions/20534417/what-is-the-difference-between-baud-rate-and-bit-rate

In Network layer the TCP/IP model supports internetworking protocol in short known as IP. The IP uses four protocols internally: ARP, RARP, ICMP & IGMP.

ARP

• ARP stands for Address Resolution Protocol
• ARP finds the physical address(mac) by using the IP address.
• ARP protocol is used to find the physical address of a device whose internet address (IP address) is known.

RARP

• RARP stands for Reverse Address Resolution Protocol
• RARP protocol helps to find the internet address of a device whose physical address is known.

ICMP

• ICMP stands for Internet Control Message Protocol
• IP in network layer sends data in form of small packets known as datagrams.
• ICMP protocol sends the datagrams problems back to sender.
• It is used for query and error reporting messages.

IGMP

• IGMP stands for Internet Group Message Protocol
• IGMP protocol is used for simultaneous transmission of a message to a group of recipients.

• PAN or  Personal Area Network  is a computer network that enables communication between computer devices near a person.
• PANs can be wired, such as USB or FireWire, or they can be wireless, such as infrared, ZigBee, Bluetooth and ultrawideband, or UWB. The range of a PAN typically is a few meters

Protocol – A protocol is a set of rules that govern data communication following are the key elements of protocol

1. Timing refers to two characteristics.
2. When data should be sent and
3. How fast they can be sent.

Medium
Transmission medium is the physical path by which a message travels from sender to receiver

Link
A link (or edge) of a network (or graph) is one of the connections between the nodes (or vertices) of the network.

Protocol – A protocol is a set of rules that govern data communication following are the key elements of protocol

1. Timing refers to two characteristics.
2. When data should be sent and
3. How fast they can be sent.

Medium
Transmission medium is the physical path by which a message travels from sender to receiver

Routing
Routing is a process which is performed by network layer devices in order to deliver the packet by choosing an optimal path from one network to another.

Path
Connection between  nodes

The Application layer is present at the top of the OSI model. It is the layer through which users interact. It provides services to the users. What message is to be sent or the message format, syntax and semantics. A user has access to application layer for sending and receiving messages.

Point to Note

• Application Layer protocol
• TELNET
• FTP
• TFTP
• NFS
• SMTP
• LPD(Line Printer Daemon)
• X window
• SNMP
• DNS
• DHCP

• AMPS
  The first generation (1G) of cellular mobile communication systems, called Advanced Mobile Phone System (AMPS) in North America, used analog FM in 30 kHz channels and accommodated multiple users through frequency division multiple access in the 800–900 MHz band allocated by the 1976 World Allocation Radio Conference
• CDMA
  IS – 95 is a second generation cellular phone system based on CDMA and DSSS. IS-54 and IS-136 are second-generation (2G) mobile phone systems, known as Digital AMPS (D-AMPS)
• B-CDMA
  The Third generation cellular phone system will provide universal personnel communication.

Broadband code division multiple access (B-CDMA) is a CDMA-based cellphone technology that uses broadband transmission. It is an improvement over the first-generation CDMA, which uses narrowband transmission. This kind of technology allows for better deployment of transmitter signals.

Session layer provides dialog control, token management and Synchronization, as services.

1. Dialog Control : This layer allows two systems to start communication with each other in half-duplex or full-duplex.
2. Token Management: This layer prevents two parties from attempting the same critical operation at the same time.
3. Synchronization : This layer allows a process to add checkpoints which are considered as synchronization points into stream of data. Example: If a system is sending a file of 800 pages, adding checkpoints after every 50 pages is recommended. This ensures that 50 page unit is successfully received and acknowledged. This is beneficial at the time of crash as if a crash happens at page number 110; there is no need to retransmit 1 to100 page

Refer : https://www.studytonight.com/computer-networks/osi-model-session-layer

• Repeaters are network devices operating at physical layer of the OSI model that amplify or regenerate an incoming signal before retransmitting it.
• They are incorporated in networks to expand its coverage area. They are also known as signal boosters.

• Number of entries in lookup table = 2¹⁰ = 1024
• Size of each entry  in lookup table = 8 bits for R component + 8 bits for G component + 8 bits for B component = 24 bits = 3 Bytes
• Size of lookup table = Number of entries in  * size of each entry
• Size of lookup table =1024 * 3 = 3072 Bytes
• 3072 Bytes = 1024 +2048 (2¹⁰ + 2¹¹) bytes

UTP is the Unshielded Twisted Pair cable. It consists of two unshielded wires twisted together. These are used extensively in Local-Area-Networks LANs and telephone cables

• 26 letters ×2 (Capital letters and small letters) + 20 characters(10 symbols +10 numerals) = 52+20=72 .
• log₂72 = flor(6.something)= 7
• So minimum we require 7 bits to represent 72 symbols
• If you don’t want to codify both capital letters and small letters but only one family of 26 letters and be done with it, then you have 26+20=46 symbols = log₂46 =6 bits
• So minimum we require 6 bits to represent 46 symbols

option(A) : True
The firewall prevents unauthorized access to your internal, trusted network from outside threats.

option(B) : True
A virtual private network (VPN) extends a private network across a public network and enables users to send and receive data across shared or public networks as if their computing devices were directly connected to the private network. Applications running across a VPN may therefore benefit from the functionality, security, and management of the private network. Encryption is a common, although not an inherent, part of a VPN connection.

Serial-In Serial-Out Shift Register (SISO) 
The shift register, which allows serial input (one bit after the other through a single data line) and produces a serial output is known as Serial-In Serial-Out shift register.

Serial-In Parallel-Out shift Register (SIPO) 
The shift register, which allows serial input (one bit after the other through a single data line) and produces a parallel output is known as Serial-In Parallel-Out shift register

Parallel-In Serial-Out Shift Register (PISO) 
The shift register, which allows parallel input (data is given separately to each flip flop and in a simultaneous manner) and produces a serial output is known as Parallel-In Serial-Out shift register.

Parallel-In Parallel-Out Shift Register (PIPO) 
The shift register, which allows parallel input (data is given separately to each flip flop and in a simultaneous manner) and also produces a parallel output is known as Parallel-In parallel-Out shift register.

SNMP

• SNMP stands for Simple Network Management Protocol
• it is an application layer protocol which uses UDP port number 161/162.
• SNMP is used to monitor the network, detect network faults and
• SNMP is used to  to configure remote devices.

• TCP uses congestion window for congestion control and Advertisement window for flow control
• UDP does not handle congestion or flow control because no field are there in UDP header to control flow or congestion

255.255.255.248
11111111.11111111.11111111.11111000
255.255.255.248/29 mask
NID = 29 bits
Host ID =32-29=3 bits

• In transparent mode, the router is, essentially, invisible to the traffic. Traffic goes in one port and out the other "untouched" in the same way that it passes through a switch. It's more accurate to say that a transparent firewall is like a switch with an ability to inspect frames.
• In transparent mode, the firewall is an L2 device and not an L3 or routed hop. Since the transparent mode firewall is not a routed hop, it can be easily introduced into an existing network without IP readdressing

• Distance vector  is a  dynamic routing algorithm in which each router computes distance between itself and each possible destination i.e. its immediate neighbors.
• The router share its knowledge about the whole network to its neighbors and accordingly updates table based on its neighbors.
• The sharing of information with the neighbors takes place at regular intervals.
• It makes use of Bellman Ford Algorithm for making routing tables.
• Problems – Count to infinity problem which can be solved by splitting horizon.
  – Good news spread fast and bad news spread slowly.
  – Persistent looping problem i.e. loop will be there forever.

• Packet switching is a connectionless network switching technique.
• Message is divided and grouped into a number of units called packets that are individually routed from the source to the destination. There is no need to establish a dedicated circuit for communication.
• Each packet in a packet switching technique has two parts: a header and a payload.
• The header contains the addressing information of the packet and is used by the intermediate routers to direct it towards its destination. The payload carries the actual data.

• An IP address is a 32 bit number that uniquely identifies a network interface on a machine. An IP address is typically written in decimal digits, formatted as 4 (8 bit fields that are separated by periods)
• Each 8-bit field represents a byte of the IPv4 address.
• The bytes of the IPv4 address are further classified into two parts: the network address and the host address
• The size of the host address and network address depends upon the class of the address in classful IP addressing.
• Class A : 1       -  126 (N.H.H.H)
• Class B : 128  -  191 (N.N.H.H)
• Class C : 192  -  223 (N.N.N.H)
• Class D : 224  - 239
• Class E : 240   - 255

• Internet layer is a packet switching network based on connectionless communication
• Host send packets into the network and then the packets travel independently to their destination since the sender is not directly connected to the receiver
• it means IP is connectionless. Data packet can travel from sender to receiver without the recipient having to send an acknowledgement to the sender

Token bus is a network implementing the token ring protocol over a virtual ring on a coaxial cable. A token is passed around the network nodes and only the node possessing the token may transmit. If a node doesn't have anything to send, the token is passed on to the next node on the virtual ring. Each node must know the address of its neighbour in the ring, so a special protocol is needed to notify the other nodes of connections to, and disconnections from, the ring In a token-ring network, the token and data is passed to the next physical node along the line, but in a token bus network, it does not matter where the nodes are physically located since token-passing is done via a numeric sequence of node addresses.

Source : wiki

Following screenshot taken from : Silberschatz Galvin and Gagne

• Ethernet address is nothing but MAC Address which is present on NIC and is supposed to be unique. Thus it is unique over the Internet.
• The Main difference is IP address can change with the change in network but your device MAC address is unchanged in different networks.

Bias = 2^N−1 −1
N−Number of bits to represent exponent in binary

Given -40.1
(40)₁₀ = (101000)₂

For converting Fractional part into binary form just multiply with 2 until it get the same number

• 0.1 * 2 =0.2  - 0
• 0.2 * 2 =0.4  - 0
• 0.4 * 2 =0.8  - 0
• 0.8 * 2 =1.6   - 1
• 0.6 * 2 =1.2   - 1
• 0.2 * 2 =0.4  - 1 // stop coz 0.2*2 we already did it is repeating

(0.1)₁₀ =0.00011

(40.1)₁₀ = 101000.00011 =  1.0100000011 * 2⁵

• Biased exponent = actual + bias = 5+bias
• where bias=2⁸⁻¹−1=127
• Biased exponent = 5+127=132 = (1000 0100)₂
• sign = 1
• Mantisa = 010100000011 ....00

Therefore, number represented as 1  1000 0100  010100000011 ....00

on converting to hexadecimal we get (0xC2206666)₁₆

• The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switching network with distributed control and one of the first networks to implement the TCP/IP protocol suite.
• Both technologies became the technical foundation of the Internet.
• The ARPANET was established by the Advanced Research Projects Agency (ARPA) of the United States Department of Defense.

• Communication between a computer and a keyboard involves simplex transmission.
• In simplex transmission, data flows in single direction which in this case refers to the data flowing from the keyboard to the computer.
• Another Example would be of the mouse where the data flows from the mouse to the computer only.
•  No data flows from computer to keyboard.
• Simplex Transmission : Data can be transmitted in only one directions
• HALF DUPLEX : Data can be transmitted in both directions on a single carrier but not at the same time
• FULL DUPLEX : Data can be transmitted in both directions on a single carrier  at the same time

• PAN or  Personal Area Network  is a computer network that enables communication between computer devices near a person.
• PANs can be wired, such as USB or FireWire, or they can be wireless, such as infrared, ZigBee, Bluetooth and ultrawideband, or UWB. The range of a PAN typically is a few meters

IPv6 was developed by the Internet Engineering Task Force (IETF) to deal with the long-anticipated problem of IPv4 address exhaustion. IPv6 is intended to replace IPv4. In December 1998, IPv6 became a Draft Standard for the IETF, who subsequently ratified it as an Internet Standard on 14 July 2017

Symmetric key Encryption
Blowfish, AES, RC4, DES, RC5, and RC6
The most widely used symmetric algorithm is AES-128, AES-192, and AES-256.

Asymmetric Key Encryption
EIGamal, RSA, DSA, Elliptic curve techniques, PKCS, Diffie-Hellman, ECC(Ellipse Curve Cryptography)

DES: Data Encryption Standard)
DES(Data Encryption Standard) is an implementation of a Feistel Cipher. It uses 16 round Feistel structure. The block size is 64-bit. Though, key length is 64-bit, DES has an effective key length of 56 bits, since 8 of the 64 bits of the key are not used by the encryption algorithm (function as check bits only).

IDEA: International Data Encryption Algorithm (IDEA)
DEA operates on 64-bit blocks using a 128-bit key

BLOW FISH:  Blowfish Cryptosystem
BLOW FISH is the replacement for DES or IDEA,
64-bit block cipher with variable length key. The key length is variable ,
it can be in the range of 32~448 bits
Default 128 bits key length

AES: Advanced Encryption Standard
Advanced Encryption Standard (AES) uses block size 128 and key sizes 128, 192, 256

Domain Name System (DNS) maps human readable domain names (in URLs or in email address) to IP addresses and vice versa
For example, DNS translates and maps the domain academyera.com to the IP address 151.162.110.21

• Internet Protocol version 4 (IPv4) defines an IP address as a 32 bit number
• Internet Protocol version 6 (IPv6) using 128-bits for the IP address, was standardized in 1998

ACK number in TCP tells which byte it is expecting to receive next.

• If Initial sequence number was from 0, then ACK number is 1000 means 1000 bytes(0-999) are successfully delivered.
• If Initial sequence number was from 1, then ACK number is 1000 means 999 bytes are successfully delivered.

Initial sequence number is not given in the question so option(d) is correct
Option (C) is not possible because Initial sequence number cannot be negative(-1)

Convert the given decimal number into binary equivalent number and perform AND operation

IP address: 125.134.112.66
IP address: 01111101 10000110 01110000 01000010

Subnet Mask: 255.255.224.0
Subnet Mask: 11111111 11111111 11100000 00000000

Now Perform AND operations between IP and Mask we get

Subnet Mask:  11111111.   11111111.   11100000.00000000
IP address:       01111101. 10000110.01110000.01000010
___________________________________________________
NID :                    01111101.10000110.01100000.00000000
___________________________________________________

Network Address = 125.134.96.0

Convert the given decimal number into binary equivalent number and perform AND operation

IP address: 125.134.112.66
IP address: 01111101 10000110 01110000 01000010

Subnet Mask: 255.255.224.0
Subnet Mask: 11111111 11111111 11100000 00000000

Now Perform AND operations between IP and Mask we get

Subnet Mask:  11111111.   11111111.   11100000.00000000
IP address:       01111101. 10000110.01110000.01000010
___________________________________________________
NID :                    01111101.10000110.01100000.00000000
___________________________________________________

Network Address = 125.134.96.0

Convert the given decimal number into binary equivalent number and perform AND operation

IP address: 125.134.112.66
IP address: 01111101 10000110 01110000 01000010

Subnet Mask: 255.255.224.0
Subnet Mask: 11111111 11111111 11100000 00000000

Now Perform AND operations between IP and Mask we get

Subnet Mask:  11111111.   11111111.   11100000.00000000
IP address:       01111101. 10000110.01110000.01000010
___________________________________________________
NID :                    01111101.10000110.01100000.00000000
___________________________________________________

Network Address = 125.134.96.0

Given data
No. of requests generated = 70 request/sec
Time slot unit = 50 msec
Number of time slots in 1 second = 1000/50 = 20 seconds
Channel Load = No. of requests in 1 sec / No. of slots in 1 sec
Channel Load = 70/20 = 3.5

Given decimal value convert into binary
144. 16. 68. 117
144. 16. 68. 01110101

255.255.255.224
255.255.255. 11100000

Perform AND operation between 144. 16. 68. 117 and 255.255.255.224
144. 16. 68.      01110101
255. 255. 255.  11100000
------------------------------
144. 16. 68.      01100000(96)
-----------------------------
144.16.68.96 is not matching with Destination

Now Checking with 255. 255. 255. 0
Perform AND operation between 144. 16. 68. 117 and 255.255.255.0
144. 16. 68.      01110101
255. 255. 255. 00000000
------------------------------
144. 16. 68.     00000000
-----------------------------
144.16.68.0 is  matching with Destination

Given
Memory access time =100ns
One Frame Period = 125 us(1 us =1000ns)
In time division switches 2nT = 1 frame period,
where T = memory access time.
Max number of Lines = 125*1000/100*2=625

Given
Bandwidth B = 10 Mbps
Propagation time T_p= 25 microsec

For frame size to be minimum, its transmission time should be equal to twice of one way propagation delay.
T_FR = 2 x T_p
Let Minimum frame size is L bits.
T_FR = L / B
L=T_FR * B
where B is the bandwidth

Coming  into the problem

T_FR = 2 x 25 microsec
T_FR =  50 microsec
So In worst case a station needs to transmit for a period of 50 microseconds to detect the collision
Minimum size of the frame is 10 Mbps * 50 micro seconds = 500 bits or 63 Bytes
So this is actually the minimum size of the frame for standard Ethernet

IF 100 user are making 10 request per sec then total number of requests are 1000
∴ Total Number of Requests per second = 1000

Each SLOT is of 50 m sec then the number of slots in 1 second = 1/(50 * 10^-3) = 20 slots/sec
∴ Total Number of slots in 1 second = 20
Channel Load = Number of request in 1 sec / Number of slots in 1 sec
Channel Load = 100/20=50

Class B has 16384 (2¹⁴) Network addresses
Host addresses are 65534 (2¹⁶-2)

∴2^m = 2ⁿ-2 = 2¹⁴ = 2¹⁶-2
m=14, n=16
Now we have to check all the options
Substitute  8m and 7n
8*14 = 16 = 7*16
112=112

In class B (N.N.H.H) NID part is First 2 octet and remaining 2 octets are host id part
So, Here First 3 bits of the 3rd octet are used for subnet and remaining 10 bits for hosts
∴ Maximum number of subnets = 2³ = 8
∴ Total Number of host in each subnet = 16-3=13 bits
∴ Total Number of host in each subnet =2⁽¹³⁾-2 =8190
2 is subtracted because, 1st IP of this subnet will be subnet ID and last IP of this subnet will be the Direct Broadcast Address

Repeater
A repeater operates at the physical layer. Its job is to regenerate the signal over the same network before the signal becomes too weak or corrupted so as to extend the length to which the signal can be transmitted over the same network.

Hub
A hub is basically a multiport repeater. A hub connects multiple wires coming from different branches
Types of Hub : Active Hub , Passive Hub

Gateway
A gateway, as the name suggests, is a passage to connect two networks together that may work upon different networking models. They basically work as the messenger agents that take data from one system, interpret it, and transfer it to another system. Gateways are also called protocol converters and can operate at any network layer.

Routers
A router is a device like a switch that routes data packets based on their IP addresses. Router is mainly a Network Layer device. Routers normally connect LANs and WANs together and have a dynamically updating routing table based on which they make decisions on routing the data packets. Router divide broadcast domains of hosts connected through it.

Bridge
A bridge operates at data link layer. A bridge is a repeater, with add on the functionality of filtering content by reading the MAC addresses of source and destination. It is also used for interconnecting two LANs working on the same protocol. It has a single input and single output port, thus making it a 2 port device.
Types of Bridges : Transparent Bridges, Source Routing Bridges

Shannon Capacity (Noisy Channel)
In presence of Gaussian band-limited white noise, Shannon-Hartley theorem gives the
maximum data rate capacity
C = B log2 (1 + SNR)
where SNR Signal to noise ration
This theorem gives an upper bound of the data rate which can be reliably transmitted over a thermal-noise limited channel.

Given
Bandwidth = 3000 Hz
SNR = 30 db
Maximum data rate capacity C = B log2 (1 + SNR)
Maximum data rate capacity C= 3000 log2 (1 + 30)
Maximum data rate capacity C= 3000 log2 *(31) = 3000 * 4.9 =14,850 ≈ 15,000 

• Bit stuffing refers to inserting a 0 in user stream to differentiate it with a flag.
• Bit stuffing is required when there is a flag of bits to represent one of the incidents like start of frame, end of frame.
• If same flag of bits appear in the data stream, a zero can be inserted by the sender.
• When the receiver sees this  0 bit from the data stream, it automatically destuffs the 0 bit before sending the data to the network layer.

Shannon Capacity (Noisy Channel)
In presence of Gaussian band-limited white noise, Shannon-Hartley theorem gives the
maximum data rate capacity
C = B log2 (1 + SNR)
where SNR Signal to noise ration
This theorem gives an upper bound of the data rate which can be reliably transmitted over a thermal-noise limited channel.

Given
Bandwidth = 6 kHz
SNR = 16 db
Maximum data rate capacity C = B log2 (1 + SNR)
Maximum data rate capacity C= 6 log2 (1 + 16)
Maximum data rate capacity C= 6 log2 *(17) = 6 * 4.08 =24.74  

ARP

• ARP stands for Address Resolution Protocol
• ARP finds the MAC Address by using the IP address.
• ARP protocol is used to find the physical address(MAC Address) of a device whose internet address (IP address) is known.

RARP

• RARP stands for Reverse Address Resolution Protocol
• RARP protocol helps to find the internet address(IP Address) of a device whose MAC Address is known.

• A user datagram is encapsulated in an IP datagram.
• There are 2 fields in the IP datagram  that defines total length and length of the header.
• Subtract the length of a UDP datagram that is encapsulated in an IP datagram, then we get the length of UDP user datagram.

Congestion control refer to mechanism used to control congestion or prevent congestion.

Congestion control mechanism can be broadly classified into 2 categories :

1. Open Loop
2. Closed Loop Congestion Control

Open Loop Congestion Control
Open Loop Congestion Control applied to prevent congestion before it happens.
The congestion control is handled either by the source or the destination.

Open loop congestion control Policies are

• Retransmission Policy
• Window Policy
• Discarding Policy
• Acknowledgment Policy
• Admission Policy

Closed Loop Congestion Control
Closed loop congestion control technique is used to treat or alleviate congestion after it happens.

Some of techniques are :

• Backpressure Technique
• Choke Packet Technique
• Implicit Signaling
• Explicit Signaling
  (i) Forward Signaling
  (ii) Backward Signaling

• IEEE 802.11 standard for  wireless LANs use a media access control protocol called (CSMA/CA) stands for Carrier-Sense Multiple Access/Collision Avoidance
• While the name is similar to Ethernet's Carrier Sense Multiple Access with Collision Detection (CSMA/CD), the operating concept is totally different.

Pretty Good Privacy (PGP) is an encryption program that provides cryptographic privacy and authentication for data communication.

PGP is used for signing, encrypting, and decrypting texts, e-mails, files, directories to increase the security of e-mail communications. Phil Zimmermann developed PGP in 1991

Symmetric key algorithm used in PGP version 2 was IDEA

In cryptography, the International Data Encryption Algorithm (IDEA), originally called Improved Proposed Encryption Standard (IPES), is a symmetric-key block cipher designed by James Massey of ETH Zurich and Xuejia Lai and was first described in 1991.

The algorithm was intended as a replacement for the Data Encryption Standard (DES). IDEA is a minor revision of an earlier cipher Proposed Encryption Standard (PES).

IDEA was used in Pretty Good Privacy (PGP) v2.0 and was incorporated after the original cipher used in v1.0, BassOmatic, was found to be insecure. IDEA is an optional algorithm in the OpenPGP standard.

First 3 (N.N.N,H) octet of class C is NID bits and last octet is host bits
∴ Subnet Mask = 255.255.255.0
∴ In Binary 11111111.11111111.11111111.00000000
∴ Total Number of 1's = 24
∴ Total Number of 0's = 8

Acknowledgement field in a segment defines the sequence number of the byte which is to be received next
it means sequence number of byte that the sender should transmit next.

we need 5 subnets, each with at least 16 hosts.
∴ Subnet Mask = 255.255.255.240 provides 16 subnets with 14 hosts which is less than 15,
∴ Subnet Mask = 255.255.255.224 provides 8 subnets, each with 30 hosts
∴ Subnet Mask = 255.255.255.192 provides 4 subnets, each with 60 hosts
Comparing all the possible masks, 255.255.255.224 is better

NLSP
-NLSP stands for NetWare Link Services Protocol
-NLSP provides link-state routing.
-NLSP was developed by Novell to replace RIP routing protocols.

SAP
-SAP  stands for Service Advertisement Protocol
-SAP advertises network services.

NCP
-NCP stands for  NetWare Core Protocol
-NCP provides client-to-server connections and applications.

RIP
-RIP stands for Routing Information Protocol
-RIP is a dynamic routing protocol which uses hop count as a routing metric to find the best path between the source and the destination network
-RIP is a distance vector routing protocol.

Network support layers :
- The network support layers are Physical layer, Data link layer and Network layer.
- These deals with electrical specifications, physical connection, transport timing and reliability.

User support layers :
- The user support layers are: Session layer, Presentation layer, Application layer.
- These allow interoperability among unrelated software system.

Transport layer links these layers by segmenting and rearranging the data. It uses protocols like TCP and UDP.

-  Classful addressing is a concept that divides the available address space of IPv4 into five classes namely A, B, C, D and  E.

-  Nowadays, this concept has become obsolete and has been replaced with classless addressing because large ratio of the available addresses in a class(Class A, Class B, Class C, Class D)  in classful addressing is wasted.

-  IP addresses, before 1993 use the classful addressing where classes have a fixed number of blocks and each block has a fixed number of hosts.

-  In classless addressing, one can reserve the number of IP addresses required by modifying the CIDR value and make sure that not many addresses are wasted.

Given Ethernet destination Address = 07-01-12-03-04-05
Now to find the type of address we need to check first octant (07)
Convert given number into Binary
07 - 0000 0111

-If LSB bit 0 then Unicast
-If LSB bit 1 then Multicast
-If All Bits are 1 then Broadcast

So ( 07 - 0000 0111 ) LSB bit 1 so it is Multicast

-OTP stands for One Time Password
-OTP is more secure than a static password, especially a user-created passwords which can be weak and/or reused across multiple accounts.
-One-time password  is an automatically generated per Access and it cannot be brute forced

• In classless addressing  there are no classes, but the addresses are still granted in blocks.

• In classless addressing, when an entity, small or large, needs to be connected to Internet, it is granted a block or range of addresses.

• The size of the block (the number of addresses) varies based on the nature and size of the entry. For example, a household may be given only two addresses; a large organization may be given thousands of addresses. An ISP, may be given thousands or hundreds of thousands based on the number of customer it may serve.

• To simplify the handling of addresses, the Internet authorities impose three restrictions on classless address blocks:

1) The addresses in a block must be contiguous, one after the other.
2) The number of addresses in a block must be a power of 2 (1, 2, 4,8, …. ).
3) The first address must be evenly divisible by the number of address.

For example, a block of addresses (both in binary and dotted decimal notation) granted to a small business that needs 16 addresses.

Below figure contains certain restrictions are applied to this block.
The addresses in a block are contiguous
Number of addresses is a power of 2 (2⁴ = 16)
First address is divisible by 16.
The first address, converted to decimal number, is 3,440,387,360
which divided by 16 results in 215,024,210.

fragmentation is the process of breaking the IP packet into multiple packets of smaller size

- The main disadvantage of fragmentation is exit gateway, all the packets should exit via the same gateway.
- It requires overhead to repeatedly fragment and reassemble a large packet.
- When a large packets arrives at a gateway, it breaks the packet into fragments.
- Each fragment is then addressed to the same exit gateway. Because of fragmentation there may be chance of a DoS attack.
- Fragmentation is done at routers which make them complex to implement when routers take too much time to fragment packets this may lead to DOS attack to other packets

Wireless transmission can be categorized into 3 broad groups:
1.Radio waves
2.Microwaves
3.Infrared

-Electromagnetic waves ranging in frequencies between 3 KHz and 1 GHz are normally called radio waves.
-Electromagnetic waves ranging in frequencies between 1 and 300 GHz are normally called microwaves.
-Infrared signals have frequencies between 300 GHz to 400 THz. They are used for short range communication.

• SMTP stands for Simple Mail Transfer Protocol.
• SMTP is part of the application layer of the TCP/IP protocol.
• SMTP provides a mail exchange between users on the same or different computers
• SMTP Using a process called "store and forward" SMTP moves your email on your machine to other machine  across internet based on e-mail addresses
• SMTP works closely with something called the Mail Transfer Agent (MTA) to send your communication to the right computer and email inbox.

Bridges

• Connect two parts of the same network.
• Read only the destination address of each Ethernet packet or Token Ring frame for maximum speed and efficiency.
• Bridges operate at the Data-Link Layer of the OSI Model. They can distinguish between local and remote data, so data traveling from one workstation to another in the same segment doesn't have to cross the bridge.
• Bridges operate on MAC-Layer addresses.

Click this link for solution : https://academyera.com/data-structures-nielit-scentist

Client Machine that places the request to server machine to access the data
Server machine process the request and sends the response to the client machine

click this link for solution : https://academyera.com/nielit-scientific-assistance-it-15-10-2017-osi-tcp-layers-2

• A communication protocol is a system of rules that allow two or more entities of a communications system to transmit information via any kind of variation of a physical quantity.
• The protocol defines the rules, syntax, semantics and synchronization of communication and possible error recovery methods.
• Communicating systems use well-defined formats for exchanging various messages.
• Each message has an exact meaning intended to elicit a response from a range of possible responses pre-determined for that particular situation.

Source : Wifi

Refer this link for solution : https://academyera.com/kvs-2018-part-b-osi-tcp-layers-2

• Bandwidth in a network is the capacity of a wired or wireless network communications channel to transmit the maximum amount of data from one point to another over a computer network or internet connection in a given amount of time
• In other words Network Bandwidth is the maximum amount of data transmitted over an communications channel in a given amount of time

BUS provides the highest data rate to an individual device
BUS is a communication pathway connecting two or more devices

• X.25 is an ITU-T standard protocol suite for packet-switched data communication in wide area networks (WAN).
•  X.25 specification defines only the interface between a subscriber (DTE) and an X.25 network (DCE)
• The X.25 model was based on the traditional telephony concept of establishing reliable circuits through a shared network, but using software to create "virtual calls" through the network. These calls interconnect "data terminal equipment" (DTE) providing endpoints to users, which looked like point-to-point connections. Each endpoint can establish many separate virtual calls to different endpoints.
• One DTE-DCE interface to an X.25 network has a maximum of 4095 logical channels on which it is allowed to establish virtual calls and permanent virtual circuits

Refer this link for solution : https://academyera.com/kvs-2018-part-b-osi-tcp-layers-2

Question is not valid they have to mention which class type there using without that we cant determine the subnet even 100 is not a valid IP address

• Short for Media Access Unit, a MAU is also known as an Ethernet transceiver or MSAU (Multi Station Access Unit) is an adapter, connector, or stand alone device that enables a network device to be connected to a token ring network.
• A MAU is one form of fault tolerance that helps prevent issues if a network device or computer goes down and are commonly available as either active or passive.
• An active MAU is not powered and does not in any way strengthen the signal from a device.
• A passive MAU is powered and repeats and strengthens a signal.

In OSI network architecture, the routing is performed by network layer which is also called layer 3 with the help of intermediate routers

Refer this link for solution https://academyera.com/kvs-2018-application-layer-protocol-3

Given
Guard bands are 300 Hz
10 signals each require 3000  HZ
∴ 10 signals requires 10 x 3000 = 30000 Hz
9 (10-1) Guard bands (or gaps) needs =300 x 9 = 2700 Hz
So Minimum Bandwidth is required for the multiplexed channel =30000 + 2700 = 32700Hz

Given Time Period  is  1000 ms
we already know that Frequency is the inverse of Time Period. so
Frequency = ( 1 / Time Period )
Frequency = ( 1  / 1000 ms )
Frequency =  (1 / 1 s)   // 1000 ms = 1 sec
Frequency = 1Hz  // 1 Hz = 10^-3 kHz
Frequency =10^-3 KHz