distrbuted system

1. JINKA UNIVERSITY
COLLEGE OF NATURAL AND COMPUTATIONAL SCIENCE
DEPARTMENT OF COMPUTER SCIENCE
COURSE TITLE: Introduction Distributed System
Course code: CoSc40
Group assignment
Name Id
1. Melkamu Tsibika ………………………….. RU1708/12
2. Zena Sinshaw …………………………. RU0430/12
3. Melkamu Ermias ………………………… RU1826/12
4. Eshetu Jemberu …………………………. RU0381/12
5. Yeshwork Tesfaw ………………………….. RU0897/12
6. Fami Tahir ………………………….. RU1175/12
Instructor: Mengistu E. (M.sc.)
Subimission date 04/08/2023
Jinka, Ethiopia

2. Reliable group
communication
Such services guarantee that messages are
delivered to all members in a process group.

3. Basic Reliable-Multicasting
Schemes
• What is reliable multicasting?
• It means that a message that is sent to a process group
should be delivered to each member of that group.
• To cover such situations, a distinction should be made
between reliable communication when processes are
assumed to operate correctly.

4. • Underlying communication system means that a multicast
message may be lost part way and delivered to some, but
not all, of the intended receivers.
Basic Reliable-Multicasting
Schemes

5. Basic Reliable-Multicasting
Schemes

6. Basic Reliable-Multicasting
Schemes

7. Basic Reliable-Multicasting
Schemes
Detect missing
message

8. Return a negative
acknowledgment
Basic Reliable-Multicasting
Schemes

9. Scalability in Reliable
Multicasting
• The main problem with the reliable multicast scheme just
described is that it cannot support large numbers of
receivers
1. Swamped with such feedback messages (a feedback
implosion.)
2. Returning only negative acknowledgments, in theory,
will be forced to keep a message in its history buffer
forever.

10. Nonhierarchical Feedback
Control
• To resolve the key issue to scalable, the Scalable Reliable
Multicasting (SRM) protocol developed by Floyd et al. (1997) and works
as follows.
• In SRM
1. receivers never acknowledge the successful delivery
2. report only when they are missing a message
3. it multicasts its feedback to the rest of the group.
4. Allow another group member to suppress its own feedback.
=> only a single request for retransmission reaches S

11. Nonhierarchical Feedback
Control

12. Nonhierarchical Feedback
Control

13. Nonhierarchical Feedback
Control
Feedback suppression has shown to scale reasonably well,
But has a number of serious problems

14. • Ensuring that only one request for retransmission is
requires a reasonably accurate scheduling of feedback
messages at each receiver => not easy to archive
• Interrupts those processes to which the message has
been successfully delivered =>other receivers are force to
receive that are useless to them.
Nonhierarchical Feedback
Control

15. • Achieving scalability for very large groups of receivers
requires that hierarchical approaches are adopted.
Hierarchical Feedback Control

16. Hierarchical Feedback Control
Coordinator
at root

17. Hierarchical Feedback Control
• Coordinator at root
• Has its own history buffer

18. Hierarchical Feedback Control
Multicasting scheme
for small groups

19. Hierarchical Feedback Control
• If a member misses a
message m -> it asks
the coordinator to
retransmit m.

20. Hierarchical Feedback Control
• If the coordinator
acknowledgments for
message m from all
members -> remove m
from its history buffer.

21. • The main problem is the construction of the tree.
• A tree needs to be constructed dynamically.
• A local coordinator in the way just described is not easy to
do.
• It is a difficult problem -> no single best solution exists.
Hierarchical Feedback Control