ExtensibleServicesDiscover/A Gentle Introduction

ESD (Excerpt from Google Doc)

Service Discovery Protocol In general, each service defines its own protocol to be used by scripts making a request to the server. Server-specific protocols used in XiMP conference demo are outlined in the next section. But in order to make a request to a service, the requester must know how to send the request to the appropriate. That is, it needs to know the address of the server. For inter-object chat messages in SL, the simplest way of doing this with LSL is to use a chat channel number that is hard coded into both the service script and the requester script share. But this has a number of limitions. ...

The Service Discover Protocol (SDP, aka ESD) is a protocol for service requesters to dynamically detect the presence (and communication channel identifier) of any service it desires.