1. Communication
Chapter 2

2. Stream –Oriented Communication
RPCs and Messages focus on exchanging independent and complete units of information
Communication timing does not affect correctness
It may however affect the performance
Timing is crucial for certain applications
Continuous media
Temporal relationships are critical to correctness
Discrete media
Timing is not critical to correctness

3. Data Streams Sequence of data units – E.g. Unix Pipes, TCP/IP
Three transmission modes
Asynchronous – Orderly transmission of data units
Synchronous – Maximum end-to-end delay is specified
Isynchronous – Data units are transferred on time
Simple and Complex streams

4. Data Stream Architecture

5. Streams and Quality of Service
Properties for Quality of Service:
The required bit rate at which data should be transported.
The maximum delay until a session has been set up
The maximum end-to-end delay .
The maximum delay variance (jitter)
The maximum round-trip delay.

6. Network Level Solutions
Differentiated Services
Expedited forwarding
Assured forwarding

7. Buffering to Reduce Jitter

8. Handling Packet Loss
Forward error correction codes
Interleaving

9. Interleaving to Handle Packet Loss

10. Synchronization Mechanisms (1)
Figure The principle of explicit synchronization on the level data units.

11. Synchronization Mechanisms (2)
Figure The principle of synchronization as supported by high-level interfaces.

12. Multicast Communication
Sending data to multiple recipients
Important for several distributed applications
IP-level multicasting
Setting up communication path is complex
Most ISPs do not support multicasting
Next-best alternative – Supporting multicast at the middleware level
Also known as application-level multicasting or overlay-based multicasting

13. Application-Level Multicasting
Multicast groups
Nodes of a multicast group organize into an overlay
Collaboratively disseminate data
Tree-based overlays
Simple and (relatively) more efficient
Susceptible to node and link failures
Mesh-based overlays
Provides better failure resilience
Scribe system

14. Performance Issues with Overlay-based Multicast

15. Metrics for Application-level Multicast
Link stress
Stretch
Tree cost

16. Epidemic-style Communication
Low overhead techniques to achieve multicasting
Mimics how diseases spread
Infected, susceptible and removed
Anti-entropy technique
Rumor spreading/gossiping