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CORE BASED TREES CBT MULTICAST ROUTING ARCHITECTURE PDF

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its place in the range of multicast solutions, just as each of the unicast routing protocols has its we also present an overview of Protocol Independent Multicast (PIM) 21] { the Section 4 introduces the Core Based Tree (CBT) architecture. protocol. Besides CBT's capability to authenticate tree-joining host's and routers, . the CBT multicast protocol for IP networks based on this new architecture. Finally, Part D o ers a general architectural overview and discussion on the CBT. Core Based Trees (CBT) Multicast Routing Architecture. Status of this Most multicast algorithms build one multicast tree per sender (subnetwork), the tree being rooted at the sender's subnetwork. 11 Bootstrap Mechanism Overview.


Core Based Trees Cbt Multicast Routing Architecture Pdf

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Core Based Trees (CBT version 2) Multicast Routing. -- Protocol The CBT architecture is described in [1]. This document is CBT Functional Overview. Trees. (CBT). An Architecture for Scalable. Inter-Domain. Multicast. Routing . routing protocol. (CBT) for 1P net- works based on this new architecture .. of the unicast address space. A diagram showing a single-core. CBT tree is shown. We proceed to present a new multicast architecture, designed for best-effort, we also present an overview of P rotocol I ndependent Multicast (PI M) [21] - the .. A core-based tree involves having a single node, or router, which acts as a.

Source-based multicast trees are either built by a distance-vector style algorithm, which may be implemented separately from the unicast routing algorithm as is the case with DVMRP , or the multicast tree may be built using the information present in the underlying unicast routing table as is the case with PIM-DM [ 7 ].

The other algorithm used for building source-based trees is the link-state algorithm a protocol instance being M-OSPF [ 8 ]. Distance-Vector Multicast Algorithm The distance-vector multicast algorithm builds a multicast delivery tree using a variant of the Reverse-Path Forwarding technique [ 9 ]. The technique basically is as follows: when a multicast router receives a multicast data packet, if the packet arrives on the interface used to reach the source of the packet, the packet is forwarded over all outgoing interfaces, except leaf subnets with no members attached.

A "leaf" subnet is one which no router would use to reach the souce of a multicast packet.

Core-based trees

If the data packet does not arrive over the link that would be used to reach the source, the packet is discarded. The receiving router then checks its leaf subnets for group membership, and checks whether it has received a prune from all of its downstream routers downstream with respect to the source. If so, the router itself can send a prune upstream over the interface leading to the source.

State that expires in this way is referred to as "soft state". Interestingly, routers that do not lead to group members are incurred the state overhead incurred by prune messages.

For wide-area multicasting, which potentially has to support many thousands of active groups, each of which may be sparsely distributed, this technique clearly does not scale.

Link-State Multicast Algorithm Routers implementing a link state algorithm periodically collect reachability information to their directly attached neighbours, then flood this throughout the routing domain in so-called link state update packets.

Deering extended the link state algorithm for multicasting by having a router additionally detect group membership changes on its incident links before flooding this information in link state packets. Each router then, has a complete, up-to-date image of a domain's topology and group membership. On receiving a multicast data packet, each router uses its membership and topology information to calculate a shortest-path tree rooted at the sender subnetwork.

Provided the calculating router falls within the computed tree, it forwards the data packet over the interfaces defined by its calculation. Hence, multicast data packets only ever traverse routers leading to members, either directly attached, or further downstream. That is, the delivery tree is a true multicast tree right from the start.

However, the flooding reliable broadcasting of group membership information is the predominant factor preventing the link state multicast algorithm being applicable over the wide-area.

The other limiting factor is the processing cost of the Dijkstra calculation to compute the shortest-path tree for each active source. The Motivation for Shared Trees The algorithms described in the previous sections clearly motivate the need for a multicast algorithm s that is more scalable. CBT was designed primarily to address the topic of scalability; a shared tree architecture offers an improvement in scalability over source tree architectures by a factor of the number of active sources where source is usually a subnetwork aggregate.

Shared trees eliminate the source S scaling factor; all sources use the same shared tree, and hence a shared tree scales O G. The implication of this is that applications with many active senders, such as distributed interactive simulation applications, and distributed video-gaming where most receivers are also senders , have a significantly lesser impact on underlying multicast routing if shared trees are used.

Secondly, routers between a non-member sender and the delivery tree are not incurred any cost pertaining to multicast, and indeed, these routers need not even be multicast-capable -- packets from non-member senders are encapsulated and unicast to a core on the tree. This was an important design decision, and one, we think, was taken with foresight; once multicasting becomes ubiquitous, router state maintenance will be a predominant scaling factor.

For example, a broadcast- type lecture with a single sender or limited set of infrequently changing senders could have its core placed in the locality of the sender, allowing the CBT to emulate a shortest- path tree SPT whilst still maintaining its O G scaling characteristic.

More generally, because CBT does not incur source-specific state, it is particularly suited to many sender applications. This is the so-called "data driven" approach -- there is no set-up protocol involved.

Ballardie Experimental [Page 7] RFC CBT Multicast Routing Architecture September It is not as easy to achieve the same degree of robustness in shared tree algorithms; a shared tree's core router maintains connectivity between all group members, and is thus a single point of failure.

Protocol mechanisms must be present that ensure a core failure is detected quickly, and the tree reconnected quickly using a replacement core router. This simplicity can lead to enhanced performance compared to other protocols.

To achieve this, a host first expresses its interest in joining a group by multicasting an IGMP host membership report [ 5 ] across its attached link. For example, if a router's upstream neighbour becomes unreachable, the router immediately "flushes" all of its downstream branches, allowing them to individually rejoin if necessary.

Transient unicast loops do not pose a threat because a new join message that loops back on itself will never get acknowledged, and thus eventually times out. There is no concept of "incoming" or "outgoing" interfaces, though it is necessary to be able to distinguish the upstream interface from any downstream interfaces. In CBT, these interfaces are known as the "parent" and "child" interfaces, respectively.

With regards to the information contained in the multicast forwarding cache, on link types not supporting native multicast transmission an on-tree router must store the address of a parent and any children.

On links supporting multicast however, parent and any child information is represented with local interface addresses or similar identifying information, such as an interface "index" over which the parent or child is reachable.

When a multicast data packet arrives at a router, the router uses the group address as an index into the multicast forwarding cache. A copy of the incoming multicast data packet is forwarded over each interface or to each address listed in the entry except the incoming interface. Each router that comprises a CBT multicast tree, except the core router, is responsible for maintaining its upstream link, provided it has interested downstream receivers, i.

A child interface is one over which a member host is directly attached, or one over which a downstream on-tree router is attached. One keepalive message is sent to represent entries with the same parent, thereby improving scalability on links which are shared by many groups. On multicast capable links, a keepalive is multicast to the "all-cbt-routers" group IANA assigned as If a parent link does not support multicast transmission, keepalives are unicast.

This group-carrying echo reply is not prompted explicitly by the receipt of an echo request message. A child is notified of the time to expect the next echo reply message containing group information in an echo reply prompted by a child's echo request. The frequency of parent group reporting is at the granularity of minutes. Also, in the paper, multicast routing protocols are briefly summarized and optical burst switched WDM networks are investigated with the proposed multicast schemes.

Core-Based Tree (CBT)

Introduction In our century, internet is an indispensable technology and the main reason of the increasing internet traffic is the ever growing demands of the users. Thus, new technologies are needed for high-bandwidth intensive applications to provide enough bandwidth. WDM optical network is proposed to deal with this problem. Optical network occupies local to wide area, connects millions of users, and offers high data rates and capacities exceeding those of familiar networks.

WDM technology well utilizes the high-bandwidth characteristic of the fiber-optic links. In the concept of WDM over fiber-optic link, the laser beams travel over a single fiber where each laser beam travels over a different optical wavelength [ 1 ]. Hence, on these days, WDM networks become the most preferred architecture for backbone networks with the many advantages they own. The first one is the ability of building robust multicast trees with the optical layer topology instead of electronic layer.

The other one is the ability of light-splitting which is more efficient than copying IP packets.

1. Introduction

The last one is the bit-rate transparency in optical multicast. Furthermore, multicast services' needed applications are also gaining great concern. Multicasting is a way of sending information from a single or multiple sources to many destinations. Recently, multicasting in optical domain gains much more attention than multicasting in electronic domain because of the light-splitting capability of optical switches and because these optical switches present excellent solutions instead of duplicating data in electronic domain [ 2 — 4 ].

The paper is organised as follows. In Section 2 , WDM networks' general structure is presented.

Optical WDM networks and main topics about multicasting are briefly summarized in Section 3. In the last section, a new multicasting protocol for OBS is proposed.

General Properties of WDM Networks As the bandwidth intensive application usage increases, the bandwidth demand increases too. Therefore, WDM is presented to meet this increasing need for very-high-bandwidth transport networks. With the WDM technology, it is easy to build very large wide-area networks. Thus, internet, video-on-demand, distributed interactive simulation, graphics and visualization, worldwide web browsing, e-commerce, medical image access and distribution, shared whiteboards, teleconferencing, and many more bandwidth intensive applications demand multicast services.

On the other hand, these multicast applications belong to the category of multipoint applications. Furthermore, multicast services' needed applications are also gaining great concern. Multicasting is a way of sending information from a single or multiple sources to many destinations.

WDM Network and Multicasting Protocol Strategies

Recently, multicasting in optical domain gains much more attention than multicasting in electronic domain because of the light-splitting capability of optical switches and because these optical switches present excellent solutions instead of duplicating data in electronic domain [ 2 — 4 ]. The paper is organised as follows.

In Section 2 , WDM networks' general structure is presented. Optical WDM networks and main topics about multicasting are briefly summarized in Section 3.

In the last section, a new multicasting protocol for OBS is proposed. General Properties of WDM Networks As the bandwidth intensive application usage increases, the bandwidth demand increases too.

Therefore, WDM is presented to meet this increasing need for very-high-bandwidth transport networks. With the WDM technology, it is easy to build very large wide-area networks. Thus, internet, video-on-demand, distributed interactive simulation, graphics and visualization, worldwide web browsing, e-commerce, medical image access and distribution, shared whiteboards, teleconferencing, and many more bandwidth intensive applications demand multicast services.

On the other hand, these multicast applications belong to the category of multipoint applications. The first service is one-to-many which includes most of the applications such as on-demand video distribution, network news distribution, file distribution, and document distribution.

The second service, many to one, includes resource discovery, data collection at a central location, auctions, group polling, and accounting. The last service many to many applications are multimedia conferencing, distance learning, and distributed simulations. The transmission rates of these applications are on the order of subwavelength rates. This means that some of the applications do not need the whole transmission rates of a lightpath.

Therefore, for this kind of applications, traffic grooming is required. In the traffic grooming technique, different traffic streams are switched into higher-speed streams. There are many traffic grooming models in the literature but most of them are designed for unicast traffic. It is obvious that the network design and traffic structures of unicast traffic and a multicast traffic are different from each other.

For example, in order to support a multicast traffic, the packets need to be duplicated but in a unicast traffic there is no need for packet duplication. In unicast connections, a path should be routed from source to destination.The sending of the acknowledgement causes the router to add the interface to its child interface list in its forwarding cache for the group, if it is not already.

A core router need not be configured to know it is a core router. Ballardie Experimental [Page 7] RFC CBT Multicast Routing Architecture September It is not as easy to achieve the same degree of robustness in shared tree algorithms; a shared tree's core router maintains connectivity between all group members, and is thus a single point of failure.

Default: 3. With the WDM technology, it is easy to build very large wide-area networks. We followed by describing the features and components of the architecture, illustrating its simplicity and scalability.

Bootstrap Message Format 8.