11-10-2012, 04:45 PM
Stream-Oriented Communication
Communication3.ppt (Size: 4.17 MB / Downloads: 68)
Media: means by which information is conveyed
Types of media
Discrete media
No temporal dependence between data items
ex) text, still images, object code or executable files
Continuous media
Temporal dependence between data items
ex) Motion - series of images
For example, a movie composed of
A video stream of low-quality images of 320x240 pixels, i.e., 76,800 bytes video data units;
A audio stream: audio samples group into units of 11,760 bytes, each corresponding to 33 ms of audio;
If the input process can handle 2.5 MB/sec, lip synchronization is achieved by alternating between reading an image and reading a block of audio samples every 33 ms.
Multicast application examples
Financial services
Delivery of news, stock quotes, financial indices, etc
Remote conferencing/e-learning
Streaming audio and video to many participants (clients, students)
Interactive communication between participants
Data distribution
e.g., distribute experimental data from Large Hadron Collider (LHC) at CERN lab to interested physicists around the world
Pros and Cons
Scalability
Routers do not maintain per-group state
End systems do, but they participate in very few groups
No need for globally consistent naming, allow application specific naming
Potentially simplify support for higher level functionality
Leverage computation and storage of end systems
Leverage solutions for unicast congestion, error and flow control
Efficiency concerns
redundant traffic on physical links
increase in latency due to end-systems
System structure
The overlay comprises of :
A central source (may be replicated for fault tolerance)
A number of overcast nodes (standard PCs with lot’s of storage)
- organized into a distribution tree rooted at the source
- bandwidth efficient trees
Final Consumers – members of the multicast group
- allows unmodified HTTP clients to join