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IP Multicast Channels: EXPRESS Support for Large-scale Single-source Applications. Authors: Hugh W. Holbrook and David R. Cheriton Presenter: Mridul Sharma. Contents. Introduction IP Multicast Channels ECMP Multi-source Multicast Applications Cost and Scalability - PowerPoint PPT Presentation
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IP Multicast Channels: EXPRESS Support for Large-scale Single-source Applications
Authors: Hugh W. Holbrook and David R. Cheriton
Presenter: Mridul Sharma
Contents
• Introduction
• IP Multicast Channels
• ECMP
• Multi-source Multicast Applications
• Cost and Scalability
• Costing Overhead and Proactive Counting
• Conclusion
Focus
Provide explicit support for large-scale multicast applications by extending the IP Multicast service model to support multicast channels
IP Multicast: Group Model
• Hosts aggregated into groups with single address
• Good for multicast discovery & small scale meetings over the internet
Problems
• Strained for very large scale multicast applications such as Internet TV– Violates common ISP billing models– Provides no indication of group size– No restriction on allowed senders– World-wide unique multicast address– Scaling IP multicast routing for conventional
group semantics remains an issue
IP Multicast Channels
• A multicast channel is a datagram delivery service identified by a tuple (S, E) where S is the sender’s source address and E is a channel destination address.
• Only the source host S may send to E.
Channel vs. Group Addressing
S S
(S,E)
G
Single-source IP Multicast Addresses
• 224 class D addresses allocated by IANA
• Routers identify a channel multicast datagram by its destination address
• Same service interface as IP Multicast for packet transmission to, and reception on, a channel
222.0.0.0 239.255.255.255
IP Multicast addresses
Single-source multicastAddresses (232.*.*.*)
EXPRESS Service Interface Extensions
• Source service interface– Count = CountQuery(channel, countId,
timeout)
– channelKey(channel, K(S, E) )
• Subscriber service interface– Result = newSubscription(channel [, K(S, E) ]),
– Count(channel, countId, count)
Advantages
• Source– 224 channels per source– Address management is simplified– Authenticated subscription option– CountQuery mechanism (number of subscribers
or subscriber vote)
Advantages (Contd.)
• Subscriber– Receives traffic only from the source it
designates– Ability to provide feedback
Advantages (Contd.)
• ISP– Provides basis for charging– Counting facility increases revenue– EXPRESS is relatively simple to implement
and manage
EXPRESS Count Management Protocol
• A single common management protocol
• Maintains both the distribution tree and supports source-directed counting and voting
• RPF is used to route subscriptions and unsubscriptions towards the source
ECMP
• Generic Counting Operation– CountQuery– Count– CountResponse– A router can initiate a query without source co-
operation
ECMP (Contd.)
• Distribution Tree Maintenance– New subscription– Unsubsciption– Router can use either TCP or UDP mode for
ECMP
ECMP: Subscription
ECMP (Contd.)
• Neighbor Discovery– Periodic CountQuery message– countId: neighbors; all channels
• EXPRESS Packet Forwarding– Forwarding Information Base entries at each
router– Forwarding procedure is nearly identical to IP
Multicast
ECMP (Contd.)
• Authenticated ECMP vs. End-to-end Encryption– Authentication provides restricted access while
encryption provides confidentiality
ECMP Advantages
• Simple integrated protocol– Supports subscription, multicast channel
maintenance and counting
• No change in host OS if it supports IP Multicast
• Multicast traffic travel only along paths from source to subscribers
Multi-source Multicast Applications
• Multiple channels, one per source– Applicable when new source is going to transmit for
extended period of time
• Several sources sharing a channel using higher level relaying through the channel’s source host – Supported by middleware layer for session
management
The Session Relay Approach
Advantages of SR Approach
• Appropriate placement of SRs to minimize communication is under application control
• Applications can have additional backup SRs for fault tolerance, placement, switching over etc– “Hot” and “cold” standby
• SR can provide application-specific functionality
Session Relaying
• As an ISP Service
• For other applications
• Cost/ Performance
Cost and Scalability
• Cost of router FIB memory for channels
• Cost of management-level router state
• Cost of maintaining this state
Counting Overhead & Proactive Counting
• Counting Overhead– Small for large-scale channels if approximated
over long time periods– Excessive use of counting is expensive
• Proactive Counting– Receivers and routers proactively send count
messages upstream
Related Work
• Service Models and Routing
• Accounting
• Counting
Conclusions
• Straightforward extension to the conventional IP multicast
• Simple implementation
• Additional capabilities like access control, accounting and local-to-host multicast address allocation
• Almost single source and truly multi source multicast applications can be implemented