1. Advanced Operating System
Group Communication
Hello! Everyone,
My name is Shinya Kobayashi. Today, I am going to present our paper titled “Inter-Cluster Job Coordination Using Mobile Agents” on behalf of the first author, Munehiro Fukuda. Munehiro was hoping to show up and present the paper at AMS2001, however he got to wait in Japan until he will get an H1B visa. Since I received the presentation materials from him quite recently, please allow me to present this paper using this script.
I can respond to your questions as far as I know, however you can also ask Munehiro by . His address is on the title page of our paper.
(time 1:05)
7/6/2018
Advanced Operating System

2. Advanced Operating System
Group Communication
Communication types:
One-to-many: broadcast
Many-to-one: synchronization, collective communication
Many-to-many: gather and scatter
Group addressing
Multicast address
Broadcasting
One-to-one communication
Performance drawback on bus-type networks
Simpler for switching-based networks
Semantics
Send-to-all, bulletin-board semantics
0-, 1-, m-out-of-n, all-reliable
7/6/2018
Advanced Operating System

3. Advanced Operating System
Atomic Multicast
Send-to-all semantics and all-reliable
Simple emulation:
A repetition of one-to-one communication with acknowledgment
What if a receiver fails
Time-out retransmission
What if a sender fails before all receivers receive a message
All receivers forward the message to the same group.
A receiver discard the 2nd or the following messages.
7/6/2018
Advanced Operating System

4. Advanced Operating System
Message Ordering
R1 and R2 receive m1 and m2 in a different order!
Some message ordering required
Absolute ordering
Consistent ordering
Causal ordering
FIFO ordering S1 R1 R2 S2 m2 m1 m1 m2
7/6/2018
Advanced Operating System

5. Advanced Operating System
Absolute Ordering
Rule:
Mi must be delivered before mj if Ti < Tj
Implementation:
A clock synchronized among machines
A sliding time window used to commit message delivery whose timestamp is in this window.
Example:
Distributed simulation
Drawback
Too strict constraint
No absolute synchronized clock
No guarantee to catch all tardy messages
Ti < Tj Ti mi Tj mi mj mj
7/6/2018
Advanced Operating System

6. Advanced Operating System
Consistent Ordering
Rule:
Messages received in the same order (regardless of their timestamp).
Implementation:
A message sent to a sequencer, assigned a sequence number, and finally multicast to receivers
A message retrieved in incremental order at a receiver
Example:
Replicated database updation
Drawback:
A centralized algorithm
Ti < Tj Ti Tj mj mj mi mi
7/6/2018
Advanced Operating System

7. Advanced Operating System
Causal Ordering
Rule:
Happened-before relation
If eki, eli ∈h and k < l, then eki → eli,
If ei = send(m) and ej = receive(m), then ei → ej,
If e → e’ and e’ → e”, then e → e”
Implementation:
Use of a vector message
Example:
Distributed file system
Drawback:
Vector as an overhead
Broadcast assumed S1 R1 R2 R3 S2 m4 m1 m1 m4 m2 m2 m3
From R2’s view point m1 →m2
7/6/2018
Advanced Operating System

8. Advanced Operating System
FIFO Ordering
Rule:
Messages received in the same order as they were sent.
Implementation:
Messages assigned a sequence number
Example:
TCP
This is the weakest ordering. S R m1
Router 1 m2 m1 m3 m2 m4 m3
Router 2 m4
7/6/2018
Advanced Operating System