Author Topic: Hybrid Multicast  (Read 455 times)


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Hybrid Multicast
« on: September 25, 2013, 06:23:32 PM »
Hybrid Multicast

To reduce the performance penalty of OM, Zhang proposed a hybrid multicast
framework called Universal Multicast (UM). The basic idea is to fully utilize native IP
multicast wherever available and automatically construct an overall multicast session via
unicast tunnels between regions of the network supporting native IP multicast, called
islands. Isolated IP multicast islands in LANs, especially in enterprise networks and
campus networks, exist, even though universal deployment has been slow. To take
advantage of the IP multicast performance gain, these available IP multicast islands can
be utilized to build an UM wherever possible. To provide ubiquitous multicast delivery
services, unicast tunnels between IP multicast islands are built. Multicast messages are
transmitted via native IP multicast protocols within the islands and encapsulated in
unicast packets to transmit through the tunnels from one island to another. Since native
group management protocols donít extend beyond the islands, a mechanism to coordinate
the membership across the islands is needed. For hybrid multicast, typically at least two
types of protocols are needed: an intra-island and an inter-island group management
protocol. P2P OM protocols can be utilized as the inter-island multicast protocol; the
Internet Group Management Protocol (IGMP) may be used for the intra-island subgroup
multicast. An alternative or even complementary approach to using multicast tunneling is
to use an overlay to adaptively combine native multicast regions with overlay multicast.
Peers that are members of a multicast group that are in a common native multicast region
can map their multicast paths to the native multicast protocol. He and Ammar have
analyzed a hybrid architecture combining host-group multicast with multi-destination
multicast. Combining these elements, we can see a hybrid multicast architecture that uses
native multi-destination routing for small groups for overlay performance enhancement,
native host-group routing for larger groups, and overlay multicast to combine native
islands into single group sessions. To leverage performance and cost, today the
information technology (IT) industry and the telecommunications industry are also
looking into the feasibility of hybrid peer-to-peer system for Internet video and IPTV
services. Some popular approaches include content popularity weighted and managed
overlay-based approaches. In a content popularity weighted approach, popular content is
offloaded from the server and the low-cost peer-to-peer overlay is used to improve
system scalability. The long tail content, on the other hand, is served primarily by the
content server to ensure reliability and QoS. Managed overlay takes control of content
delivery via server or content delivery networks (CDNs). The servers act like the
supernodes in hybrid P2P networks. Consumers (peers) supply bandwidth and storage
when needed.