D.Magdalene, AP/CSE

COMPUTER NETWORKS UNIVERSITY QUESTION

What is DNS?

The domain name system (DNS) is the way that Internet domain names are located and translated into Internet Protocol addresses. A domain name is a meaningful and easy-to-remember "handle" for an Internet address.

What is PGP?

Pretty Good Privacy (PGP) is a popular a technique developed by Philip Zimmerman used to encrypt and decrypt e-mail over the Internet. PGP is often used for signing, encrypting, and decrypting texts, e-mails, files, directories, and whole disk partitions and to increase the security of e-mail communications.

Define Kerberos

Kerberos  is a computer network authentication protocol which works on the basis of 'tickets' to allow nodes communicating over a non-secure network to prove their identity to one another in a secure manner. Kerberos was developed in the Athena Project at the Massachusetts Institute of Technology (MIT).

What is overlay networks?

An overlay network is a computer network which is built on the top of another network. Nodes in the overlay can be thought of as being connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network. For example, distributed systems such as cloud computing, peer-to-peer networks, and client-serverapplications are overlay networks because their nodes run on top of the Internet. 

What is MPEG?

The Moving Picture Experts Group (MPEG) is a working group of experts that was formed by ISO and IEC to set standards for audio and video compression and transmission. MPEG algorithms compress data to form small bits that can be easily transmitted and then decompressed. MPEG achieves its high compression rate by storing only the changes from one frame to another, instead of each entire frame.

What is IPV6?

Internet Protocol Version 6 (IPv6) is a network layer protocol that enables data communications over a packet switched network. IPv6 uses a 128-bit address, allowing 2128, or approximately 3.4×1038 addresses. IPv6 is often referred to as the "next generation Internet"

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because of it's expanded capabilities and it's growth through recent large scale deployments. IPv6 protocol was published by the Internet Engineering Task Force (IETF) in 1998.

What is internetworking?

 When two or more networks or network segments are connected using devices such as a router that provide a common method of routing information packets between the networks then it is called as internetworking. The resulting system of interconnected networks is called an internetwork, or simply an internet.

What is Computer Network?

A computer network is a group of computer systems and other computing hardware devices that are linked together through communication channels to facilitate communication and resource-sharing among a wide range of users.

What is bridge?

A bridge is a device that separates two or more network segments within one logical network (e.g. a single IP-subnet). A bridge is usually placed between two separate groups of computers that talk with each other, but not that much with the computers in the other group. A good example of this is to consider a cluster of Macintoshes and a cluster of UNIX machines.

What is flow control?

Flow control is the process of managing the rate of data transmission between two nodes to prevent a fast sender from overwhelming a slow receiver. It provides a mechanism for the receiver to control the transmission speed, so that the receiving node is not overwhelmed with data from transmitting node.

What is slow start?

Slow-start is part of the congestion control strategy used by TCP. Slow-start is used in conjunction with other algorithms to avoid sending more data than the network is capable of transmitting, that is, to avoid causing network congestion.

What is flooding?

Flooding is a simple routing algorithm in which every incoming packet is sent through every outgoing link except the one it arrived on. Flooding is used in bridging and in systems such as Usenet and peer-to-peer file sharing and as part of some routing protocols, including OSPF, DVMRP, and those used in ad-hoc wireless networks.

What is congestion?

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Congestion is a situation in Communication Networks in which too many packets are present in a part of the subnet, performance degrades. Congestion in a network may occur when the load on the network (i.e. the number of packets sent to the network) is greater than the capacity of the network (i.e. the number of packets a network can handle.)

What is congestion control?

Congestion Control refers to techniques and mechanisms that can either prevent congestion, before it happens, or remove congestion, after it has happened. Congestion control mechanisms are divided into two categories, one category prevents the congestion from happening and the other category removes congestion after it has taken place.

What is HTTP?

HyperText Transfer Protocol defines how messages are formatted and transmitted, and what actions Web servers andbrowsers should take in response to various commands. For example, when you enter a URL in your browser, this actually sends an HTTP command to the Web server directing it to fetch and transmit the requested Web page.

What is FDDI?

FDDI (Fiber Distributed Data Interface) is a set of ANSI and ISO standards for data transmission on fiber optic lines in a local area network (LAN) that can extend in range up to 200 km (124 miles). The FDDI protocol is based on the token ring protocol. FDDI is frequently used on the backbone for a wide area network (WAN).

What is HTML?

HTML or HyperText Markup Language is the main markup language for creating web pages and other information that can be displayed in a web browser. HTML is written in the form of HTML elements consisting of tags enclosed inangle brackets (like <html>), within the web page content. 

What is cryptography?

Cryptography is the practice and study of techniques for secure communication in the presence of third parties. it is about constructing and analyzingprotocols that overcome the influence of adversaries and which are related to various aspects in information security such as data confidentiality, data integrity, authentication, and non-repudiation.

What is subnetting?

Subnetting is the strategy used to partition a single physical network into more than one smaller logical sub-networks (subnets). Subnetting allows an organization to add sub-networks without the need to acquire a new network number via the Internet service provider (ISP). Subnetting

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helps to reduce the network traffic and conceals network complexity. Subnetting is essential when a single network number has to be allocated over numerous segments of a local area network (LAN).

What is subnet mask?

A Subnet mask is a 32-bit number that masks an IP address, and divides the IP address into network address and host address. Subnet Mask is made by setting network bits to all "1"s and setting host bits to all "0"s. Within a given network, two host addresses are reserved for special purpose. The "0" address is assigned a network address and "255" is assigned to a broadcast address, and they cannot be assigned to a host.

What is CIDR?

Classless Inter-Domain Routing is a method for allocating IP addresses and routing Internet Protocol packets. The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous addressing architecture of classful network design in the Internet. Its goal was to slow the growth of routing tables on routers across the Internet.

What is router?

A router is a device that forwards data packets alongnetworks. A router is connected to at least two networks, commonly two LANs or WANs or a LAN and its ISP's network. Routers are located at gateways, the places where two or more networks connect.

What is gateway?

A gateway is a node on a network that serves as an entrance to another network. In enterprises, the gateway is the computer that routesthe traffic from a workstation to the outside network that is serving the Web pages. In homes, the gateway is the ISP that connects the user to the internet.

What is switch?

A switch is a small hardware device that joins multiple computers together within one local area network (LAN). Ethernet switch devices were commonly used on home networks.

What is hub?

A hub is a device that connects PCs together. Hubs are commonly used to connect segments of a LAN. A hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.

What is a port?

A port is an application-specific or process-specific software construct serving as a communications endpoint in a computer's host operating system. A port is associated with an IP

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address of the host, as well as the type of protocol used for communication. The purpose of ports is to uniquely identify different applications or processes running on a single computer and thereby enable them to share a single physical connection to a packet-switched network like the Internet.

What is the purpose of subnetting?

The purpose of subnetting is

1. To divide a large network into smaller segments to reduce traffic and speed up the sections of your network.

2. To connect networks across geographical areas.3. To connect different topologies such as Ethernet, Token Ring, and FDDI

together via routers.4. To avoid physical limitations such as maximum cable lengths or exceeding the

maximum number of computers on a segment.

What are the functions of ARP

The function of Address Resolution Protocol is

To obtain the MAC address of a host, and then map that MAC address to the host's IP address.

To facilitates data exchange between computers on the same network.

What are the building blocks of network?

Client computers: The computers that end users use to access the resources of the network. 

Server computers: Computers that provide shared resources, such as disk storage and printers, as well as network services, such as e-mail and Internet access.

Network interface: An interface — sometimes called a network port — that’s installed in a computer to enable the computer to communicate over a network. 

Cable: Computers in a network are usually physically connected to each other using cable. 

Switches: Network cable usually doesn’t connect computers directly to each other. Instead, each computer is connected by cable to a device known as a switch.

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Wireless networks: In many networks, cables and switches are making way for wireless network connections, which enable computers to communicate via radio signals. 

Network software: Although network hardware is essential, what really makes a network work is software.

List the similarity between transport layer and DLL

Basically Data Layer provides error-free transmission across a single link ( 2 consecutive stations ) where as Transport layer ensures the communication between source and destination. (Provide end-to-end delivery, from one computer (host) to another.)

Thus to ensure the communication, both the layers will provide following services;

o 1. Flow Control (Which controls the flow of data ensuring no overhead to the destination)

o 2. Error Detection and Correction (Detect errors in the data and correct them if possible)

What are the features of datagram networks?

Data is transmitted from source to destination without guarantee of delivery Data is frequently divided into smaller pieces and transmitted without a defined

route or guaranteed order of delivery A datagram supports a maximum of 65,535 bytes at a time Datagram packet network is a any-to-any communication. Any device connected to such a network can inject a packet into the network

with the proper source and destination address, and the network will take it to its destination.

The network is also highly flexible. If a portion of the network fails (e.g. a link, a switching node), the surrounding

nodes can select a new path and subsequent packets will take the new route to the destination.

The datagram model is relatively simple to understand and implement. There is no complex call setup or call termination required, The system operates on the connectionless model.

List out the characteristics of frame relay.

Frame Relay Characteristics are

Preservation of the order of frame transfer from one edge of the network to the other

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Non-duplication of frames Small probability of frame loss IP Split Horizon Checking Ping Your Own IP Address on a Multipoint Frame Relay The Keyword broadcast Reconfiguring a Sub interface DLCI Limitations IP/IPX/AT Address RIP and IGRP Keepalive Serial Interfaces OSPF and Multipoint

What are the benefits of Frame Relay?

Reduced Internetworking costs Increased Performance with Reduced Network Complexity. Increased Interoperability via International Standards. Protocol Independence.

What is frame relay?

Frame relay is a telecommunication service designed for cost-efficient data transmission for intermittent traffic between local area networks (LANs) and between end-points in a wide area network (WAN). Frame relay puts data in a variable-size unit called a frame and leaves any necessary error correction (retransmission of data) up to the end-points, which speeds up overall data transmission. 

List out the advantages and disadvantages of bluetooth.

Advantages

This technology requires no cables and wires Simplicity of use Bluetooth is actually inexpensive Bluetooth is automatic Low interference Low energy consumption Sharing voice and data Upgradeable

Disadvantages

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Slow transfer speed Bluetooth only has a range of 15 to 30 feet depending on the device.  Bluetooth is much easier for a hacker to break into than secure wireless networks.

Compare IPV4 and IPV6

Description IPV4 IPV6Address 32 bits long (4 bytes).  128 bits long (16 bytes).

Address maskUsed to designate network from host portion.

Not used

Address prefix

Sometimes used to designate network from host portion.

Used to designate the subnet prefix of an address.

Address types

IPv4 addresses are categorized into three basic types: unicast address, multicast address, and broadcast address.

IPv6 addresses are categorized into three basic types: unicast address, multicast address, and anycast address.

IP headerVariable length of 20-60 bytes, depending on IP options present.

Fixed length of 40 bytes.

What is choke packet? How it is used for congestion control

A choke packet is a specialized packet that is used for congestion and flow control along a network.

A router detects congestion by measuring the percentage of buffers in use, line utilization and average queue lengths. When it detects congestion, it sends choke packets across the network to all the data sources associated with the congestion. The sources respond by reducing the amount of data they are sending.

How encoding can be done using NRZ-I techniques?

Non return to zero, inverted (NRZI) is a method of mapping a binary signal to a physical signal for transmission over some transmission media. The two level NRZI signal has a transition at a clock boundary if the bit being transmitted is a logical 1, and does not have a transition if the bit being transmitted is a logical 0. "One" is represented by a transition of the physical level. "Zero" has no transition.

What is 1-persistent CSMA?

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When the sender (station) is ready to transmit data, it checks if the transmission medium is busy. If so, it then senses the medium continually until it becomes idle, and then it transmits the message (a frame). In case of a collision, the sender waits for a random period of time and attempts to transmit again. 1-persistent CSMA is used in CSMA/CD systems includingEthernet.

What is P-persistent CSMA? 

This is a sort of trade-off between 1 and non-persistent CSMA access modes. When the sender is ready to send data, it checks continually if the medium is busy. If the medium becomes idle, the sender transmits a frame with a probability p. If the station chooses not to transmit (the probability of this event is 1-p), the sender waits until the next available time slotand transmits again with the same probability p. This process repeats until the frame is sent or some other sender starts transmitting. In the latter case the sender monitors the channel, and when idle, transmits with a probability p, and so on. p-persistent CSMA is used in CSMA/CA systems including Wi-Fi and other packet radio systems.

List some QOS parameters.

Bandwidth Latency or delay Jitter or variations Synchronization between multiple streams Packet loss ratio Packet error ratio

What are the difference between flow control and congestion control?

Flow control Congestion controlFlow control is a mechanism used in computer networks to control the flow of data between a sender and a receiver, such that a slow receiver will not be outran by a fast sender.

Congestion control is a mechanism that controls data flow when congestion actually occurs.

Mechanisms used in flow control could be categorized based on whether the receiver sends feedback to the sender.

Congestion control algorithms are classified based on the amount of feedback received from the network and the aspect of performance it aims to improve.

List out the advantages of DNS.

Achieves transparency without losing scalability Consistent on all hosts

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DNS is used on the internet Eliminate management of host tables.

Discuss the use of computer networks.

Allowing to share and exchange a variety of information File sharing Printer sharing Communication and collaboration

Write the categories of network.

The categories of network are

LAN (local area network) MAN (metropolitan area network) WAN (wide area network)

A network bandwidth of 10MBPS can pass only an average of 12,000 frames per minute with each frame carrying an average of 10,000 bits. What is the throughput of this network?

Solution

We can calculate the throughput as

The throughput is almost one-fifth of the bandwidth in this case.

What is the propagation time if the distance between the two points is 12,000 km? Assume the propagation speed to be 2.4 × 108 m/s in cable.

Solution

We can calculate the propagation time as

The example shows that a bit can go over the Atlantic Ocean in only 50 ms if there is a direct cable between the source and the destination.

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What are the propagation time and the transmission time for a 2.5-kbyte message (an e-mail) if the bandwidth of the network is 1 Gbps? Assume that the distance between the sender and the receiver is 12,000 km and that light travels at 2.4 × 108 m/s.

Solution

We can calculate the propagation and transmission time as shown:

Note that in this case, because the message is short and the bandwidth is high, the dominant factor is the propagation time, not the transmission time. The transmission time can be ignored.

What are the propagation time and the transmission time for a 5-Mbyte message (an image) if the bandwidth of the network is 1 Mbps? Assume that the distance between the sender and the receiver is 12,000 km and that light travels at 2.4 × 108 m/s.

Solution

We can calculate the propagation and transmission times as shown:

Note that in this case, because the message is very long and the bandwidth is not very high, the dominant factor is the transmission time, not the propagation time. The propagation time can be ignored.

Differentiate ARP and RARP

ARP RARP

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ARP is a computer network protocol used to convert network layer addresses to link layer addresses.

RARP is a networking protocol used in computer networks.

RFC 826 describes the ARP.  RARP is described in RFC 903 published by IETF. 

ARP maps IP addresses to hardware address

RARP maps hardware addresses to IP addresses

ARP is a logical address RARP is a physical address.

Draw the datagram format of udp

What is cipertext?

Cipher text is encrypted text. Cipher text is the result of encryption performed on plaintext using an algorithm, called a cipher. Cipher text is also known as encrypted or encoded information because it contains a form of the original plaintext that is unreadable by a human or computer without the proper cipher to decrypt it. 

List out the two modes of IP security.

IPsec supports two encryption modes:

Transport Tunnel. 

How is http related to www?

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The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web.

Define CSMA/CD.

Carrier Sense Multiple Access/Collision Detect (CSMA/CD) is the protocol for carrier transmission access in Ethernet networks. 

List the goal of QOS

The primary goal of QoS is to provide priority including dedicated bandwidth, controlled jitter and latency (required by some real-time and interactive traffic), and improved loss characteristics. The goal of QoS is to provide guarantees on the ability of a network to deliver predictable results. 

Differentiate UDP and TCP.

UDP TCPUDP has no inherent order as all packets are independent of each other. If ordering is required, it has to be managed by theapplication layer.

TCP rearranges data packets in the order specified.

UDP is faster because there is no error-checking for packets.

The speed for TCP is slower than UDP.

There is no guarantee that the messages or packets sent would reach at all.

There is absolute guarantee that the data transferred remains intact and arrives in the same order in which it was sent.

UDP Header size is 8 bytes. TCP header size is 20 bytesUDP does error checking, but no recovery options.

TCP does error checking

Eg. DNS, DHCP, TFTP, SNMP, RIP, VOIP etc...

Eg. HTTP, HTTPs, FTP, SMTP Telnetetc...

It is Connection-Less It is Connection-Oriented

Transmission Speed is very high.Transmission Speed is high but not as high as UDP.

Define Framing.

Frames Are The Small data Units Created By Data Link Layer And The Process Of Creating Frames By The Data Link Layer Is Known As Framing.

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Why are protocol needed?

Network Protocol are needed because the message or data send by our network have to reached on destination through different networks of different structure and different platform.

So network protocols are performing to duty to make the transmitted data well-suited to those new networks, which come in the way to destination.

What is the use of IP address?

An IP address is an Internet Protocol address. It is used to identify all the different computers and websites on the internet.

Each IP address is unique. It is what enables you to do things like send a message in a chat program to another computer, and out of all the millions of computers in the world, it arrives at the correct one. 

What is client Process?

The client is a process (program) that sends a message to a server process (program), requesting that the server perform a task (service).

Client programs usually manage the user-interface portion of the application, validate data entered by the user, dispatch requests to server programs, and sometimes execute business logic.

What are the two multiplexing strategies used in transport layer?

Upward multiplexing Downward multiplexing

Define security in networking.

Security is a specialized field in computer networking that involves securing a computer network infrastructure. 

Security in networking is typically handled by a network administrator or system administrator who implements the security policy, network software and hardware needed to protect a network and the resources accessed through the network from unauthorized access.

What is symmetric key algorithm?

Symmetric-key algorithms are a class of algorithms for cryptography that use the same cryptographic keys for both encryption of plaintext and decryption of cipher text.

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The keys represent a shared secret between two or more parties that can be used to maintain a private information link.

State why telnet uses network virtual terminal. Rather than having terminals and hosts communicate using their various native “languages”,

all Telnet clients and servers agree to send data and commands that adhere to a fictional, “virtual” terminal type call the Network Virtual Terminal (NVT).

The NVT defines a set of rules for how information is formatted and sent, such as character set, line termination, and how information about the Telnet session itself is sent.

What is meant by piggybacking? What are its advantages and disadvantages?

Piggybacking is a bi-directional data transmission technique in the network layer (OSI model). It makes the most of the sent data frames from receiver to emitter, adding the confirmation that the data frame sent by the sender was received successfully (ACK acknowledge). 

Advantages:

Improves the efficiency Better use of available channel bandwidth.

Disadvantages:

The receiver can jam the service if he/she has nothing to send.  Additional complexity.

How are errors caused in transmission lines?

Errors may be caused by a defect, usually understood either to be a mistake in design or construction, or a broken component.

Multiple reflections in transmission lines can cause an amplification of timing errors associated with the delay sensitivity to environment effects of the transmission lines. 

List out the function of router.

The main function of a router is

To enable the movement of data by a device from one network to another. Packet Forwarding Packet switching and Packet filtering

List the way to deal with congestion.

Determine what the traffic is

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Decide how to deal with the traffic Weigh your options

Discuss the issues in network security.

Authenticationo Process of verifying identity of a user

Integrityo Data that arrives is the same as that is sent

Confidentialityo Sensitive information should not be visible to eavesdropper - use

Encryption Non-repudiation

o Assurance that any transaction that takes place can subsequently be proved to

have taken place Authorization

Explain CRC

CRC (Cyclic redundancy check) – is often used to detect data transmission errors. It is transmitted together with the data and evaluated independently at the receiver side. If evaluated and received CRCs differ, data transmission error is indicated. If both CRCs are the same, there still exists other data provided the same CRC. Nevertheless the probability of such an error is usually very low. Transmitted data sequence can be interpreted as binary polynomial. E.g. the sequence 11000101 can be written as x7+x6+x2+1. CRC is being evaluated as a remainder after the division of data polynomial by so called generating polynomial.

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