One year before Tim Berners-Lee’s proposals for the World Wide Web.

World Wide Web still has less than 100 pages.

Traffic is routed through unicast-encapsulated tunnels between members.

Used broadcast and prune, but:

no pruning at all in the beginning, and RPF checks on neighbors to select output interfaces.

A big concert with The Rolling Stones is broadcasted.

links appear in Russia & Antarctica.

Hardware support & new protocols.

• Uses whatever unicast routing table is available (protocol independent).
• Does not do RPF checks on neighbors.

• Broadcasts group membership info within an AS.
  • Allows each router to have a complete picture.
  • Requires more state to be maintained per router.
• Shortest path trees per group are build using Dijkstra.
• Data streams is only sent to group members.

Engineers start rolling out PIM-SM in response.

Uses (like PIM-DM) the underlying unicast routing table, but introduces the concept of a rendezvous point (RP), or core,

and requires goup members to send explicit join messages.

Similar to PIM-SM, but:

Uses a single tree for all groups, resulting in less state to maintain at the cost of less optimal trees.

The tree is bidirectional, meaning that traffic from source to RP can be sent down the tree by any node. This avoids the same packets traveling in both directions at the cost of slightly higher complexity.

To manage larger networks, route aggregation and hierachical routing is needed.

There was no protocol to manage information across domain boundaries, causing routing problems to spread throughout the topology.

MBGP/PIM-SM/MSDP

Allows multicast routing across domains by exchange of reachability information.

With MBGP each AS advertises the set of routes it can reach with associated costs. Border routers can compute the set of ASs to traverse to reach any given network.

MBGP does not carry information about groups or sources, only reachable multicast-enabled networks.

Representatives (a RP) in each domain announce active sources.

Information is flooded, and each receiving peer uses RPF checks to avoid loops.

A RP is needed in each AS, serving receivers within the domain.

When a source is advertised, a join message is sent towards the source if the RP has any members for the group.

Once data is received from the source, it is forwarded down the local shared tree.

This may be solved by having MSDP peers cache SA messages, at the cost of extra complexity.

The original packets may never reach receivers since forwarding state may not yet be established.

Established state may be dropped between bursts due to timeouts.

The result is that no packets ever reach group members.

A few thousand active sources would result in a large number of SA messages (with embedded data).

It was still seen as an acceptable short-term solution at the time.

Based on the idea that there is a single logical root domain for every group.

Constructs bidirectional trees that are shared between domains and using a single root.

A strict address allocation scheme is needed to avoid interdomain dependencies.

Attempts to make fundamental changes in the multicast model in order to address issues such as security, billing and management.

The premise is that most applications are single-source or have an easily identifiable primary source.

This source acts as the root of the tree, eliminating the need for RPs.

Group members send join messages along the reverse path to the source.

Specifically designed for subscriber-based systems, such as TV broadcasts, and allows closed groups with low routing complexity.

One source must be chosen as primary, and the tree is rooted at this node’s closest router.

Receivers send join messages to the primary, constructing a bidirectional tree.

Additional sources send packets towards the primary, but traffic is routed down the tree as soon as it reaches a participating router.

“Native multicast”

High cost of deployment.

Offers ease of deployment and moves intelligence to the edge of the network.

Somewhere between, where some nodes act as gateways.

Offers more flexibility and lower cost of deployment than IP.