The Naming Service

CCC can be run on the bus model, passing all messages around a single multicast group per conference. This will scale reasonably, since it scales with the number of participants in the conference. Name resolution occurs at each host, matching the destination naming tuple in the message against the list of tuples that are registered at this particular host. However, it it does not scale indefinitely, because the load on each host and the network increases with the complexity of the conference and the number of messages. To improve scaling, the communications should be optimised so that messages are only propagated to the machines that are interested. Thus we need a service that maps the naming tuples to locations, so that intelligent mapping of message paths to locations can be performed (aka intelligent routing and placement of multicast groups). This name location service (or naming service as it is more generally known) has a number of properties that differentiate it from other naming services such as X.500 and the DNS:

• Dynamic and frequent updates.
• Fast propagation of changes.
• Ability to fall back to broadcast to interested parties when uncertain about the consistency of a refined addressing group, since names are unique per conference and are included in each message.

The last property is important, since it allows a relaxed approach to maintenance of consistency amongst the naming servers, saving greatly in the messages and complexity of the internals of the service.

We intend to implement a nameserver suitable for loosely coupled conferences as the default in the CCC library. However, CCCP will also allow the use of an external nameserver to supplement or replace the internal nameserver behaviour, which will allow much greater use of the nameserver to made in more tightly coupled conferences, for instance by using the nameserver to keep an accurate list of members.