1. Advanced Operating System
COMMUNICATION
Shrada Pradhan
Advanced Operating System
Csc CSC 8320

2. Content Flow Basic Reliable-Multicasting Schemes
Scalability in Reliable Multicasting
Nonhierarchical Feedback Control
Hierarchical Feedback Control
Atomic Multicast
Virtual synchronous multicast

3. Introduction
Services guarantee that messages are delivered to all members in a process group
Reliable multicast services are important
But reliable multicasting is not that easy.

4. Basic Reliable-Multicasting Schemes
A reliable communication in the presence of faulty process
If all the non-faulty group receive message.
A reliable communication when processes are assumed to operate correctly
Neither processes fail, nor process join or leave the group during transmission.
All the group memebers should receive the messages.

5. Contd.. Weaker multicast Unreliable multicast
Condition: The numbers of receivers are limited.
Unreliable multicast
Messages sent may be lost or not delivered to all the receivers.

6. Contd.. Solution for Unreliable Multicast
Assigning a sequence member to each message
Detect missing message
Send negative acknowledgement, requesting for retransmission
Sender retransmit the message.

7. Scalability in Reliable Multicasting
Problem
Cannot handle large number of receivers
Senders may be swapped with feedback messages
Solution
Receiver sending acknowledgement only for missing messages.
But overflows history buffer.
Removing messages after certain time.

8. Scalable multicast Non hierarchial feedback control (NHFC)
To reduce the number of feedback messages sent.
Feedback supression model is used.
Receiver sends negative acknowledgement as feedback.
Receiver multicasts its feedback to the rest of the group.
Schedules feedback messages with random time delay.

9. Scalable Multicast Hierarchial Feedback Control
Large group of receivers
Each group is partitioned into smaller subgroups in a tree
Each subgroup has a local coordinator responsible for handling retransmission requests.
Local coordinaters have own buffer history

10. Hierarchaial Feedback control

11. Contd.. Asks its parent subgroup if coordinator misses message.
If message and acknowledgement received,
clears its history buffer.

12. Limitation NHFC: HFC: Reasonable accurate scheduling is not easy.
Other receivers are forced to receive useless messages.
HFC:
Construction of tree is not easy.

13. Automatic Multicast
Message is either delivered to all or not essayed at all.
Reliable multicast with process failures.
Believes in group membership for correctly operating replicas.

14. Contd. If one process breaks then it leaves the group
After repair can join the group
And then update with the state of the rest of the members.
This maintains non-faulty process maintains consistent view
Forces reconciliation when replica recovers and rejoins the group

15. Atomatic Multicast

16. Virtual synchronous Reliable multicast property
If sender of the message crashes, it is either delivered to remaining process or ignored.

18. Different Ordering Unordered Multicast FIFO Multicast
No guarantee concerning order of delivery of messages
FIFO Multicast
Should deliver incoming messages from the same process in the same order
For eg. M1 is always delivered before M2

19. Contd. Casually Ordered Multicast Totally Ordered Multicast
Preserves potential casuality between messages
Even though m1 preceeds m2, communication layer delivers m2 after m1.
Totally Ordered Multicast
Messages should be delivered in the same ordered to all group members.

20. Contd. Casually Ordered Multicast Totally Ordered Multicast
Preserves potential casuality between messages
Even though m1 preceeds m2, communication layer delivers m2 after m1.
Totally Ordered Multicast
Messages should be delivered in the same ordered to all group members.

21. Latest Relevant knowledge
Optimistic Atomic Multicast[2]
Is expensive in terms of message delays
a protocol that combines reduced latency
increased throughput
Messages are delivered optimistically in a single communication step.
Does not rely on spontaneous message ordering for fast delivery

22. Future Work Atomic multicasts if not occurred between database nodes
Instead transaction ordering is exposed as a service that is provided by a dedicated set of nodes.
Improves transaction throughput and latency [3]
So studies can be done in such fields to enhace performance.

23. References
1. Andrew S. Tanenbaum , and Maarten Van Steen. Distributed Systems Principles and paradigms. Second Edition, 2007
2. Optimistic Atomic Multicast, Distributed Computing Systems (ICDCS), 2013 IEEE 33rd International Conference on 8-11 July 2013.
3. An Atomic-Multicast Service for Scalable In-Memory Transaction Systems, Cloud Computing Technology and Science (CloudCom), 2014 IEEE 6th International Conference on Date Dec. 2014