Communication

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 4-29. The principle of explicit
  synchronization on the level data units.

11
Synchronization Mechanisms (2)

• Figure 4-30. 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