FACULTY OF EGINEERING AND TECHNOLOGY
Distributed Systems(BCS-701)
LECTURE-05
Dr. Hariom Sharan
Professor & Dean
Computer Science & Engineering
OUTLINE
Limitation Of Distributed System
Fundamental Models
Interaction Model
Performance Of Communication Channel
References
Limitation of Distributed System
Distributed System is a collection of self-governing computer systems efficient of transmission and cooperation
among each other by the means of interconnections between their hardware and software. It is a collection of
loosely coupled processor that appears to its users a single systematic system. Distributed systems has various
limitations such as in distributed system there is not any presence of a global state. This differentiates distributed
system computing from databases in which a steady global state is maintained.
Distributed system limitations has the impact on both design and implementation of distributed systems. There are
mainly two limitations of the distributed system which are as following:
1. Absence of a Global Clock
2. 2. Absence of Shared Memory
Limitation of Distributed System
Absence of a Global Clock:
In a distributed system there are a lot of systems and each system has its own clock. Each clock on each system is
running at a different rate or granularity leading to them asynchronous. In starting the clocks are regulated to keep
them consistent, but only after one local clock cycle they are out of the synchronization and no clock has the exact
time.
Time is known for a certain precision because it is used for the following in distributed system:
Temporal ordering of events
Collecting up-to-date information on the state of the integrated system
Scheduling of processes
There are restrictions on the precision of time by which processes in a distributed system can synchronize their
clocks due to asynchronous message passing. Every clock in distributed system is synchronize with a more reliable
clock, but due to transmission and execution time lapses the clocks becomes different. Absence of global clock
make more difficult the algorithm for designing and debugging of distributed system.
Limitation of Distributed System
Absence of Shared Memory:
Distributed systems have not any physically shared memory, all computers in the distributed system have their own
specific physical memory. As computer in the distributed system do not share the common memory, it is impossible
for any one system to know the global state of the full distributed system. Process in the distributed system obtains
coherent view of the system but in actual that view is partial view of the system.
As in distributed system there is an absence of a global state, it is challenging to recognize any global property of
the system. The global state in distributed system is divided by many number of computers into smaller entities.
FUNDAMENTAL MODELS
Computation occurs within processes; the processes interact by passing messages, resulting in
communication (information flow) and coordination (synchronization and ordering of activities) between
processes. In the analysis and design of distributed systems we are concerned especially with these
interactions. The interaction model must reflect the facts that communication takes place with delays that are
often of considerable duration, and that the accuracy with which independent processes can be coordinated
is limited by these delays and by the difficulty of maintaining the same notion of time across all the computers
in a distributed system.
Failure: The correct operation of a distributed system is threatened whenever a fault occurs in any of the
computers on which it runs (including software faults) or in the network that connects them. Our model
defines and classifies the faults. This provides a basis for the analysis of their potential effects and for the
design of systems that are able to tolerate faults of each type while continuing to run correctly.
Security: The modular nature of distributed systems and their openness exposes them to attack by both
external and internal agents. Our security model defines and classifies the forms that such attacks may take,
providing a basis for the analysis of threats to a system and for the design of systems that are able to resist
them.
INTERACTION MODEL
The discussion of system architectures in indicates that fundamentally distributed systems are composed of
many processes, interacting in complex ways. For example:
• Multiple server processes may cooperate with one another to provide a service; the examples mentioned
above were the Domain Name System, which partitions and replicates its data at servers throughout the
Internet, and Sun’s Network Information Service, which keeps replicated copies of password files at several
servers in a local area network.
Two significant factors affecting interacting processes in a distributed system:
• Communication performance is often a limiting characteristic.
• It is impossible to maintain a single global notion of time.
Performance of communication channel
The communication channels in our model are realized in a variety of ways in distributed systems, for
example
By an implementation of streams
By simple message passing over a computer network
Communication over a computer network has the performance characteristics such as:
Latency The delay between the start of a message’s transmission from one process to the beginning
of its receipt by another.
Bandwidth The total amount of information that can be transmitted over a computer network in a
given time. Communication channels using the same network, have to share the available bandwidth.
Jitter The variation in the time taken to deliver a series of messages. It is relevant to multimedia data.
For example, if consecutive samples of audio data are played with differing time intervals then the
sound will be badly distorted.
References
https://www.javatpoint.com/digital-image-processing-tutorial
https://www.tutorialpoint.com/
https://www.geeksforgeeks.org/limitation-of-distributed-system/
Distributed Systems, Concepts and Design, George Coulouris, J Dollimore and Tim Kindberg, Pearson
Education, 4th Edition,2009.
Distributed Systems, Principles and paradigms, Andrew S.Tanenbaum, Maarten Van Steen, Second Edition,
PHI.
Distributed Systems, An Algorithm Approach, Sikumar Ghosh, Chapman & Hall/CRC, Taylor & Fransis
Group, 2007.
