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1.4 Yoid in a Nutshell

 

Here is a very brief overview of the key technical components of yoid: The core of yoid is a topology management protocol, called YTMP, that allows a group of hosts to dynamically auto-configure into two topologies:

• a (tunneled) shared tree topology for efficient multicast distribution of application content, and
• a (tunneled) mesh topology, for robust broadcast distribution of various information, including control information and, where appropriate, application content.

The tunnels can be either two-party (using UDP or TCP), or N-party (using very tightly scoped IP multicast). Each host can join or leave the two topologies (jointly called the tree-mesh) independently, making the group itself dynamic.

Each group has one or more rendezvous hosts associated with it. Rendezvous hosts are not attached to the tree-mesh--rather, they serve as a discovery or bootstrap mechanism for allowing hosts joining a group to find other hosts already in the tree-mesh. Group members contact a rendezvous host when they first join and when they finally quit the group (where possible). The rendezvous host maintains a list of some or all group members, and informs joining hosts of a number of these. The hosts then participate in the topology management algorithm with these already attached hosts to attach to the group.

The name of a given group consists of three components:

• the name of the rendezvous hosts (if multiple, they have the same name),
• the UDP ports the rendezvous hosts are listening on (optional, if not the default port number).
• the name of the group, which is unique to the rendezvous host.

This naming scheme both 1) allows any host (with a domain name) to locally create a globally unique group name, and 2) allows for discovery of the rendezvous host. The group name can be encoded as a URL, and for all practical purposes is a URL:

yoid://rendezvous.host.name:port/group.name

This gives you a basic picture of yoid, and is all I say about it for the time being. Later (sections 2 and 2.2 and beyond) I'll introduce all the terms and acronyms and more detail (where the devil lies).

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