disributed systems

1. V V COLLEGE OF ENGINEERING
V V Nagar, Arasoor, Tisaiyanvilai
INTERNAL ASSESSMENT TEST – II
III CSE – VI SEMESTER (BATCH 2020-2024)
Department of Computer Science and Engineering
Sub Code /Name: CP4071/ BIO INFORMATICS Date: -03-2023 ( )
Sem/Branch : III/ CSE Duration: 1:30 hrs.
Max. Marks: 100
PART - A (5 x 4 = 20 Marks)
1. Compare centralized and distribued
2. Illustrate coupling
Coupling refers to the degree to which two or more processes are interdependent.
3. Identify consistent snapshot
A snapshot algorithm is used to create a consistent snapshot of the global state of a distributed system.
Due to the lack of globally shared memory and a global clock, this is not trivially possible.
4. State crown criterion theorem
The crown criterion states that an A-computation is RSC, i.e., it can be realized on a system with
synchronous communication, if and only if it contains no crown. - For an A-execution, A is RSC if and
only if A is an S-execution.
5. What is deadlock resolution

2. Deadlock resolution involves breaking existing wait-for dependencies between the processes to resolve
the deadlock. It involves rolling back one or more deadlocked processes and assigning their resources to
blocked processes so that they can resume execution.
PART-B(2x26=52)
11. (a)(i).Enlighten the examples of distributed systems.
System Components in a Distributed System
● primary system controller.
● system data store.
● database.
(ii).Summarize the significant issues and challenges of the distributed system.
Key characteristics of distributed systems
● Resource sharing.
● Openess.
● Concurrency.
● Scalability.
● Fault Tolerance.
● Transparency.
(b)(i)Summarize NTP for synchronizing system of physical clocks in distributed systems
NTP is an internet protocol used to synchronize with computer clock time sources in a network. NTP
leverages UDP protocol over port 123, to synchronize clocks within a few seconds of the UTC time.
Each computer(OS) comes with the NTP Package
There are two types of NTP servers that you can use to provide UTC time to your network: public servers
and local servers. A public time server is owned and operated by a third party who makes it available for
use over the internet
(ii).Explain logical time and logical clocks.
Logical Clocks refer to implementing a protocol on all machines within your distributed system, so that
the machines are able to maintain consistent ordering of events within some virtual timespan.

3. 12. (a)(i)How causal order and total order is implemented in synchronous
Reasons that may lead to violation of causal ordering of messages
1. It may happen due to a transmission delay.
2. Congestion in the network.
3. Failure of a system.
Distributed program logic greatly depends on the order of delivery of messages. Several orderings on
messages have been defined: (i) non-FIFO, (ii) FIFO, (iii) causal order, and (iv) synchronous order.
(ii).Point out the key areas of applications of group communication
Group communication has many benefits in the workplace, including:
● Providing a way for group members to generate ideas and solutions to achieve their common
goal.
● Encouraging members to make decisions as a group.
● Creating a way for the team to build rapport with one another.
b)(i).Illustrate realizable with synchronous communication(RSC) execution
Realizable Synchronous Communication (RSC)
An execution can be modeled to give a total order that extends the partial order (E, ≺). a linear extension
of the execution, such that each send event is immediately followed by its corresponding receive event
in this linear extension.
(ii).Analyze the channels to simulate an execution using synchronous primitives on an
asynchronous systems
Synchronous execution means the first task in a program must finish processing before moving on to

4. executing the next task whereas asynchronous execution means a second task can begin executing in
parallel, without waiting for an earlier task to finish
PART- C (1x28=28)
16.a. A user arrives at a railway station that she has never visited before, carrying a PDA that is
capable of wireless networking. Suggest how the user could be provided with information about the
local services and amenities at that station, without entering the station’s name or attributes. What
technical challenges must be overcome? Discuss in detail.
The user must be able to acquire the address of locally relevant information as automatically as possible.
One method is for the local wireless network to provide the URL of web pages about the locality over a local
wireless network. For this to work:
(1) the user must run a program on her device that listens for these URLs, and which gives the user sufficient
control that she is not swamped by unwanted URLs of the places she passes through; and
(2) the means of propagating the URL (e.g. infrared or an 802.11 wireless LAN) should have a reach that
corresponds to the physical spread of the place itself.
b. Consider a distributed system where every node has its physical clock and all physical clocks are
perfectly synchronized. Develop an algorithm to record global state assuming the communication
network is reliable.