Transcript Neelofer Tamboli - ReliableMulticastGroup

Reliable Multicast Group
Oct 25, 2007
Neelofer T.
CMSC 621
What is Reliable Multicasting?
• Reliability could mean messages are
delivered:
• In order
• In timely manner
• No duplicates
• Processes may enter/leave the group
• Processes may fail while communicating
Reliable Multicasting Issues
• Protocol
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TCP is point-to-point
Multicast is not connection oriented
Protocols based on IP Multicast
Applications over UDP
• Reliable multicasting can cause network
congestion:
• Large amounts of data transmission since
multiple recipients
• Control messages for reliability
Small Scale Group
• For small scale group:
• Reliable, connection oriented, point-to-point
connections are feasible
• Messages have sequence numbers
• Receivers acknowledge messages
• Request retransmission of missing messages
• Large scale groups cause:
• Feedback implosion
• Congestion due to repair messages
Hierarchical Feedback Control
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RMTP (reliable multicast transport
protocol)
Designated receivers act as coordinators
for sub-groups
Receivers unicast feedback to DR
DRs retransmit data to sub-group
Hierarchy of DRs reduces load on original
sender
http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_1-2/reliable_multicast.html
SRM (Scalable Reliable Multicast)
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Receivers help each other
Receiver multicasts retransmission request
after a specific time period
Closest neighbor with requested data will
multicast the message
Distant neighbors timeout later than the
closest ones
If data is not retransmitted by anyone
when a node timesout, then it multicasts
the data
PGM (Pragmatic General Multicast)
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Ensures that all receivers can get reliable,
ordered, duplicate data or can detect
message loss
NACK based protocol
Suited for applications where messages
can join and leave group at any time
Uses routers for group control
References
• Tanenbaum and Steen, “Distributed Systems
Principles and Paradigms”
• Peled and Vardi, “Formal Techniques for
Networked and Distributed Systems”
• http://rmt.motlabs.com/
• C. Kenneth Miller, “Reliable Multicast Protocols
and Applications”
• Gemmel et al, “The PGM Reliable Multicast
Protocol”
• RFC 3940, “NACK-Oriented Reliable Multicast
Protocol (NORM)”
• Wu, “Verification analysis of Reliable
Multicast protocol”
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