Logical Data Modelling

Last Class: RPCs and RMI
• Case Study: Sun RPC
• Lightweight RPCs
• Remote Method Invocation (RMI)
– Design issues

Computer Science

CS677: Distributed OS

Lecture 1, page 1

Today: Communication Issues
• Message-oriented communication
– Persistence and synchronicity

• Stream-oriented communication

Computer Science

CS677: Distributed OS

Lecture 1, page 2

Persistence and Synchronicity in Communication
•

General organization of a communication system in which hosts are connected through a network

2-20

Computer Science

CS677: Distributed OS

Lecture 1, page 3

Persistence
• Persistent communication
– Messages are stored until (next) receiver is ready
– Examples: email, pony express

Computer Science

CS677: Distributed OS

Lecture 1, page 4

Transient Communication
• Transient communication
– Message is stored only so long as sending/receiving application are executing
– Discard message if it can’t be delivered to next server/receiver
– Example: transport-level communication services offer transient communication
– Example: Typical network router – discard message if it can’t be delivered next router or destination

Computer Science

CS677: Distributed OS

Lecture 1, page 5

Synchronicity
• Asynchronous communication
– Sender continues immediately after it has submitted the message
– Need a local buffer at the sending host

• Synchronous communication
– Sender blocks until message is stored in a local buffer at the receiving host or actually delivered to sending
– Variant: block until receiver processes the message

• Six combinations of persistence and synchronicity
Computer Science

CS677: Distributed OS

Lecture 1, page 6

Persistence and Synchronicity Combinations

2-22.1

a)
b)
Computer Science

Persistent asynchronous communication (e.g., email)
Persistent synchronous communication
CS677: Distributed OS

Lecture 1, page 7

Persistence and Synchronicity