Interview Questions.

Question 1. Define Distributed System?

Answer :

A distributed gadget is a set of impartial computers that looks to its customers as a unmarried coherent gadget.  A dispensed machine is one wherein components positioned at networked communicate and coordinate their movements most effective by passing message.

Question 2. List The Characteristics Of Distributed System?

Answer :

Programs are accomplished simultaneously 
There is not any worldwide time 
Components can fail independently (isolation, crash)
Question three. Mention The Examples Of Distributed System?

Answer :

The Internet
Intranets
Mobile and ubiquitous computing
Question four. What Is Mobile And Ubiquitous Computing?

Answer :

Mobile: Computing devices are being carried round.

Ubiquitous: Little computing devices are all around the vicinity.

Question 5. Mention The Challenges In Distributed System?

Answer :

Heterogeneity 
Openness 
Security 
Scalability 
Failure dealing with 
Concurrency 
Transparency
Question 6. What Are The Advantages Of Distributed Systems?

Answer :

Performance
Distribution
Reliability (fault tolerance)
Incremental boom
Sharing of statistics/assets
Communication
Question 7. What Are The Disadvantages Of Disadvantages Of Distributed Systems?

Answer :

Difficulties of growing dispensed software program
Networking issues
Security troubles
Question 8. Write The Difference Between Mobile And Ubiquitous Computing?

Answer :

Ubiquitous computing used in unmarried surroundings such as home or sanatorium. 
Mobile computing has gain while the usage of specific devices including laptops and printers.
Question nine. Why We Need Openness?

Answer :

The degree to which a laptop gadget can be prolonged and re-implemented. 

IEEE = Institute of Electrical and Electronic Engineers 

e.G., IEEE 802.Eleven WLAN, IEEE 802.3 Ethernet 

W3C = World Wide Web Consortium 

e.G., HTML Recommendations

Question 10. What Is The Security Mechanisms Used In Distributed Computing?

Answer :

Encryption: 

 E.G. Blowfish, RSA 

Authentication:

E.G. Password, public key authentication 

Authorization:

E.G. Get entry to manage lists

Question eleven. How We Provide A Security?

Answer :

Confidentiality:

 Protection towards disclosure to unauthorized person. 

E.G. ACLs (get right of entry to manage lists) to offer legal access to data. 

Integrity: 

 Protection against alternation or corruption. 

E.G. Converting the account range or amount value in a cash order 

Availability: 

Protection towards interference focused on access to the assets. 

E.G. Denial of provider (DoS, DDoS) attacks 

Non-repudiation:

Proof of sending / receiving an records.    

E.G. Virtual signature

Question 12. Define Scalability?

Answer :

System need to work successfully at many one of a kind scales, ranging from a small Intranet to the Internet. 

Challenges of designing scalable allotted systems: 

Cost of bodily resources 
Cost must linearly increase with device size 
Performance Loss 
For example, in hierarchically based statistics, seek overall performance loss due to facts growth need to not be beyond O (log n), wherein n is the dimensions of statistics. 

Preventing software program sources strolling out.

Numbers used to symbolize Internet deal with (32 bit->64bit), Y2K like hassle. Avoiding overall performance bottlenecks.

Use decentralized algorithms (centralized DNS to decentralized).

Question 13. What Are The Different Types Of System Model?

Answer :

Architecture version
Fundamental version
Interaction model 
Failure model 
Security version
Question 14. What Is The Use Of Middleware?

Answer :

Middleware a layer of software program whose motive is to masks heterogeneity and to offer a handy programming model to software programmers. Middleware is represented by way of processes or gadgets in a set of computer systems that interact with each different to implement communique and resource sharing support for distributed applications.

Question 15. Define Protocol?

Answer :

The time period protocol is used to refer to a well-known set of rules and formats to be used for communique among techniques with a view to carry out a given undertaking. 

The definition of a protocol has two essential parts to it: 

A specification of the collection of messages that need to be exchanged; 
A specification of the layout of the facts within the messages.
Question sixteen. What Is Meant By Internet Protocol?

Answer :

The IP protocol transmits datagram from one host to some other, if vital through intermediate routers. There are several header fields which can be used by the transmission and routing algorithms.

Question 17. Define Mobile Ip?

Answer :

Mobile IP is an Internet Engineering Task Force (IETF) standard communications protocol this is designed to permit cellular tool customers to move from one community to some other even as retaining their permanent IP cope with. Defined in Request for Comments (RFC) 2002, Mobile IP is an enhancement of the Internet Protocol (IP) that provides mechanisms for forwarding Internet traffic to mobile devices (known as cellular nodes) whilst they're connecting thru aside from their domestic network.

Question 18. What Is The Architectural Model?

Answer :

An architectural version defines the manner wherein the components of gadget interact with each other and the way in which they may be mapped onto an underlying network of computers.

Question 19. What Is The Fundamental Model?

Answer :

Fundamental models that help to show key troubles for the designers of distributed systems. Their purpose is to specify the layout troubles, problems and threats that ought to be resolved with a view to increase distribute systems that fulfill their responsibilities efficaciously, reliable and relaxed. The fundamental mode affords summary perspectives of just those characteristics of disbursed systems that have an effect on the dependability traits - correctness, reliability and protection.

Question 20. Write About The Parts Available In Routing Algorithm?

Answer :

Routing algorithm has  elements: 

It must make choices that determine the path taken by way of each packet as it travels thru the community. In circuit-switched community layers inclusive of X.25 and frame relay networks consisting of ATM the path is decided each time a virtual circuit or connection is mounted.
In packet-switched network layers which includes IP it's far determined separately for every packet, and the algorithm have to be mainly easy and green if it isn't always to degrade community overall performance.
It should dynamically replace its understanding of the network based totally on visitors tracking and the detection of configuration changes or disasters. This interest is much less time-critical; slower and greater computation-extensive strategies may be used.
Question 21. What Is Meant By Inter Process Communication?

Answer :

Inter method verbal exchange is concerned with the verbal exchange among strategies in a allotted gadget, both in its own proper and as guide for communique between allotted items.  The Java API for inter manner conversation in the internet offers each datagram and movement communication.

Question 22. What Is The Difference Between Rmi And Rpc?

Answer :

Remote Procedure Call or the RPC and the Remote Method Invocation or RMI are each message passing strategies inside the Inter Process Communication (IPC).

But there are  fundamental differences among the two methods:

RPC helps procedural programming. I.E. Handiest far off techniques may be invoked. Whereas RMI is item-primarily based. As the name suggests, it is invoked on faraway items.
In RPC, the parameters which might be surpassed are ordinary facts structures. Whereas in RMI, gadgets may be exceeded as parameters.
Question 23. Define Datagram?

Answer :

A datagram is, to cite the Internet's Request for Comments 1594, "a self-contained, impartial entity of information carrying sufficient statistics to be routed from the source to the destination pc without reliance on earlier exchanges between this source and destination computer and the transporting network." The time period is utilized in several well-known conversation protocols, together with the User Datagram Protocol and AppleTalk.

Question 24. What Is The Use Of Udp?

Answer :

The Domain Name Service (DNS), which looks up DNS names in the Internet, is applied over UDP. UDP datagram’s are now and again an appealing desire due to the fact they do no longer be afflicted by overheads associated with assured message shipping.

Question 25. What Is Meant By Client Server Communication?

Answer :

The customer–server version of computing is a dispensed software structure that walls duties or workloads between the vendors of a aid or provider, known as servers, and provider requesters, called clients.

Question 26. What Is Meant By Group Communication?

Answer :

Group communication is a multicast operation is greater suitable- this is an operation that sends a unmarried message from one system to every of the participants of a collection of process, usually in any such way that the membership of the group is transparent to the sender.

Question 27. What Is The Use Of Rmi Registry?

Answer :

The RMI registry is used to save a list of to be had offerings. A purchaser uses the registry to make it's proxy object, and the Registry is liable for giving appropriate records to the consumer in order that it could connect with the server that implements the service.

Question 28. Difference Between Synchronous And Asynchronous Communication?

Answer :

In synchronous shape of verbal exchange, the sending and receiving processes synchronize at each message. In this situation, both ship and receive are blocking off operations. Whenever a ship is issued the sending process is blocked until the corresponding get hold of is issued. Whenever get hold of is issued, the method blocks till a message arrives. 

In asynchronous shape of conversation, using the send operation is non-blockading in that the sending method is allowed to proceed as soon as the message has been copied to a nearby buffer and the transmission of the message proceeds in parallel with the sending procedure. The receive operation could have blockading and non-blocking versions.

Question 29. What Is Marshalling And Unmarshalling?

Answer :

Marshalling is the manner of taking a collection of records gadgets and assembling them right into a shape appropriate for transmission in a message. Unmarshalling is the procedure of disassembling them on arrival to supply an equal collection of information objects on the destination.

Question 30. What Is Cdr?

Answer :

CORBA CDR is the outside data representation defined with CORBA 2.Zero. CDR can constitute all the data types that can be used as arguments and go back values in faraway invocation in CORBA. It consists of 15 primitive kinds that include brief (sixteen-bit), long (32-bit), unsigned short, unsigned long, waft (32-bit), double (64-bit), char, Boolean (TRUE or FALSE), octet (eight-bit) and any constructed kinds.

Question 31. Define Xml?

Answer :

XML stands for Extensible Markup Language.
XML is a markup language similar to HTML.
XML changed into designed to hold information, no longer to show data.
XML tags aren't predefined. You should outline your own tags.
XML is designed to be self-descriptive.
XML is a W3C Recommendation.
Question 32. Define Operating System?

Answer :

An Operating System is the layer among the hardware and software.

An Operating System is responsible for the following capabilities:

Device control the usage of device drivers 
Process control the use of tactics and threads 
Interprocess communication 
Memory control 
File structures.
Question 33. List The Core Os Components With Diagram?

Answer :

Process manager: Handles the introduction of and operations upon processes. A system is a unit of aid control, which includes an address space and one or extra threads.

Thread supervisor: Thread creation, synchronization and scheduling. Threads are scheduled activities connected to strategies.

Communication manager: Communication between threads attached to exceptional methods at the same pc. Some kernels also assist communique among threads in remote procedures. Other kernels don't have any perception of other computers built into them, and an additional service is required for outside conversation. 

Memory supervisor: Management of physical and virtual reminiscence.

Supervisor: Dispatching of interrupted, machine name traps and other exceptions: manage of memory management unit and hardware caches; processor and floating point unit sign up manipulations. This is known as the Hardware Abstraction Layer in Windows NT.

Question 34. How Kernel Uses The Address Space?

Answer :

Often the kernel code and data are mapped into every cope with space at the identical location. When a technique makes a system name or an exception occurs, there may be no need to interchange to a new set of deal with mappings.

Question 35. What Is System Call Trap? How It Is Implemented?

Answer :

The invocation mechanism for assets controlled via the kernel A device call trap  is  applied by way of a machine-degree TRAP commands, which puts the processor into supervisor mode and switches to the kernel cope with space.

Question 36. What Is Execution Environment? What It Contains?

Answer :

An execution environment is the unit of resource control: a group of nearby kernel-managed sources to which its threads have get entry to.

An execution environment generally consists of: 

An cope with area; 
Thread synchronization and verbal exchange assets including semaphores and verbal exchange interfaces (for example sockets); 
Higher-level sources which includes open files and home windows.
Question 37. List The Two Types Of Thread Scheduling? Explain?

Answer :

There are two styles of thread scheduling. 

They are:

Preemptive scheduling: A thread can be suspended at any point to make manner for any other thread, even when the preempted thread could otherwise continue strolling.
Non-preemptive scheduling: A thread runs till it makes a name to the threading device, while the device may additionally de-agenda it and schedule another thread to run.
Question 38. List The Types Of Event That The Kernel Notified To The User Level Scheduler?

Answer :

There are four sorts of event that the kernel notified to the consumer stage scheduler are:

Virtual processor allocated.
Scheduler Activation blocked 
Scheduler Activation unblocked 
Scheduler Activation preempted
Question 39. Difference Between Monolithic And Micro Kernel?

Answer :

The microkernel based OS can provide potential to put in force modularity in the back of reminiscence safety barriers.
Microkernel-based OS, the variety of bugs is less than the monolithic based system.
The monolithis-primarily based OS can provide extra performance with which operations can be invoked.
Question 40. Write A Note On Lrpc With Diagram?

Answer :

An invocation of  methods on the identical gadget is known as as light weight Remote Procedure Call. 
Shared memory regions are green for patron server conversation with a one-of-a-kind region among the server and each of its neighborhood customers.
The same stack is used by purchaser and server stub.
Question forty one. What Is The Goal Of Security? List The Three Broad Classes Of Security Threats?

Answer :

The principal goal of safety is to restriction get entry to to data and assets to just those standards that are legal to have achievement. 

Security threads fall into three wide classes:

Leakage
Tampering
Vandalism
Question 42. What Are The Two Measures Taken By Jvm To Protect The Local Environment?

Answer :

The  measures taken by way of JVM to defend the neighborhood surroundings are:

The downloaded classes are stored one by one from nearby classes ,preventing them from changing nearby classes with spurious variations .
The byte codes are checked for validity. Valid java byte code is composed of java virtual machine commands from a specific set. The instructions also are checked to ensure that they'll not produce positive mistakes when this system runs such as gaining access to illegal reminiscence addresses.
Question forty three. What Is Cryptography? What Is The Use Of It?

Answer :

Cryptography is the art of encoding information in a format that best the meant recipients can get right of entry to. 

Uses:

Secrecy and integrity
Authentication
Digital signatures.
Question 44. Write A Note On Digital Signature?

Answer :

Requirement: 

To authenticate saved report files in addition to messages 
To guard in opposition to forgery 
To save you the signer from repudiating a signed document (denying their duty) 
Encryption of a file in a mystery key constitutes a signature: 

Impossible for others to carry out with out information of the important thing 
Strong authentication of file 
Strong safety towards forgery 
Weak against repudiation (signer may want to claim key was compromised).
Question forty five. What Are Credentials?

Answer :

Credentials are a hard and fast of evidence supplied with the aid of a principal when inquiring for get right of entry to to a useful resource.    
It is handy to require users to engage with the gadget and authenticate themselves on every occasion their authority is needed to perform an operation on a covered assets.
Question 46. Write A Note On X.500 Directory Service?

Answer :

It is a listing carrier. It can be in the same way as a traditional name provider but it is generally used to meet descriptive queries, designed to find out the names and attributes of different customers or machine sources.

Question 47. What Is Name Space?

Answer :

It is a set of all valid names identified by way of a selected carrier. For a call to be valid manner that the provider will try to appearance it up even though that name may also prove no longer to correspond to any object-to be unbound.

Example: The call “Two” could not probably be the name of UNIX system, whereas the integer “2’ is probably.

Question 48. What Is The Use Of Iterative Navigation?

Answer :

DNS supports the version referred to as iterative navigation. To remedy a name, a purchaser gives the call to the neighborhood call server, which attempts to remedy it. If the neighborhood name server has the call, it returns the end result right now.

Question 49. Define Multicast Navigation?

Answer :

A client multicast the name to be resolved and the required object kind to the organization of call servers. Only the server that holds the named attributes responds to the request.

Question 50. Write Short Notes On Directory Services?

Answer :

A provider that shops that shops series of binding between names and attributes and that looks up entries that match attribute based totally specification is referred to as directory provider.

Example: Microsoft’s active Directory services, X.500 and its cousin LDAP, Universe.

Question 51. What Is Clock Skew And Clock Drift?

Answer :

The immediate distinction between the readings of any  clocks is referred to as their skew.

Clock flow approach that they rely time at distinctive charges, and so diverge.

Question fifty two. What Are The Two Modes Of Synchronization? Write Their Format?

Answer :

The two modes are:

External synchronization: For a synchronization sure D>zero, and for a sourceS (t) –Ci (t)zero,real times t in I.
Question 53. How The Clock Synchronization Done In Christian’s Method?

Answer :

A unmarried time server might fail, so that they suggest the use of a collection of synchronized servers.

It does not address faulty servers.

Question fifty four. List The Design Aims And Features Of Ntp?

Answer :

To offer a carrier allowing consumer throughout the internet to be synchronized correctly to UTC.
To offer a dependable carrier that may be continue to exist lengthy losses of connectivity.
To permit customers to resynchronize sufficiently regularly to offset the prices of float determined in maximum computer systems.
To offer safety against interference with the time provider whether or not malicious or unintended.
Question fifty five. With Example Explain About Happened-before Relation?

Answer :

The passed off-earlier than relation is a partial order on events that displays a flow of information among them.

Question fifty six. Write The Rules For Updating The Clocks?

Answer :

The policies for updating the clocks are:

Initially, VI[j] =0, for i, j=1, 2...N
Just earlier than pi timestamps an occasion, it sets VI[i]:=VI[i] +1.
Pi includes the fee t=VI in every message it sends.
When pi gets a timestamp t in a message, it units Vi[j] ;=max(Vi[j],t[j]),for j=1,2..N.
Question 57. What Are The Issues Resolved By Berkeley’s Algorithm?

Answer :

The collections of computers whose clocks are to be synchronized are categorized as masters and slaves. The averaging of the clock values cancels out the individual’s clocks dispositions to run rapid or gradual. 

This overcomes the uncertainty due to message transmission time introduced inside the synchronized clock values lower back by way of the master.

Question 58. What Is Network Partition?

Answer :

The network partition may be used to split a group of reproduction managers into two or greater sub companies.

The participants of equal subgroup speak with one another but members of different subgroup can not speak with each other.

Question 59. Difference Between Reliable And Unreliable Failure Detector?

Answer :

Reliable failure detector is one that is constantly accurate n detecting a system failure. It answers methods queries with either a response of unsuspected-which, as before can simplest be a hint-or failed.

U Reliable failure detector might also produce one in every of two values whilst given the identification of a technique: Unsuspected or suspected. Both of those outcomes are suggestions, which can also or might not correctly replicate whether or not the system has truely failed.

Question 60. Define Election Algorithm? Mention The Different Algorithm?

Answer :

An algorithm for selecting a unique process to play a specific function is called an election algorithm. 

Ex: In a variant of relevant server algorithm for mutual exclusion, the server is selected from the various process.

The different algorithms are:

Ring primarily based election algorithm
Bully algorithm.
Question 61. Define Multicast Communication?

Answer :

It is the implementation of institution verbal exchange .Multicast verbal exchange requires coordination and settlement. The purpose is for members of a group to obtain copies of messages sent to the institution. Many one of a kind delivery guarantees are feasible 

Example: Agree at the set of messages received or on shipping ordering.

Question 62. List The Requirements Of Consensus Algorithm To Hold For Execution?

Answer :

The necessities of consensus algorithm to preserve for execution are:

Termination
Agreement
Integrity.
Question 63. Write A Note On Bully Algorithm?

Answer :

This set of rules permits procedure to crash all through an election. Although it assumes that message shipping among methods is reliable. It assumes that the machine is synchronous – it uses timeouts to locate a process failure.

Question sixty four. What Is Distributed Debugging?

Answer :

Distributed debugging is not anything but to check whether or not a transitory nation, in preference to a solid country has occurred in an real execution. 

This is achieved with the aid of recording a machine global state.