Asterisk: The Definitive Guide, 4th Edition

Chapter 23. Distributed Universal Number Discovery (DUNDi)

A community is like a ship; everyone ought to be prepared to take the helm.

—Henrik Ibsen

Distributed Universal Number Discovery, or DUNDi, is a service discovery protocol that can be used for locating resources at remote locations. The original intention of DUNDi was to permit decentralized routing among many peers using a General Peering Agreement (GPA). The GPA is intended to take on the role of a centralized control authority with a document to create a trust relationship among the peers in the cloud. While the idea is interesting and sound, the GPA has not taken off. That doesn’t mean the DUNDi protocol itself hasn’t found a home, though: the original intention of DUNDi has been expanded so that now it doesn’t act just as a location service, but can be used to request and pass information among peers.

How Does DUNDi Work?

Think of DUNDi as a large phone book that allows you to ask peers if they know of an alternative VoIP route to an extension number or PSTN telephone number.

For example, assume that you are connected to another set of Asterisk boxes listening for and responding to DUNDi requests, and those boxes are in turn connected to other Asterisk boxes listening for and responding to DUNDi requests. Assume also that your system does not have direct access to request anything from the remote servers.

Figure 23-1 illustrates how DUNDi works. You ask your friend Bob if he knows how to reach 4001, an extension to which ...