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 email. His email address is on the title page of our paper. (time 1:05) 7/6/2018 Advanced Operating System

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

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

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

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

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

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

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