Once you've retrieved B2buaHelper, you can use it to link two SIP sessions by creating requests using the createRequest method.
SipServletRequest clientRequest = b2buaHelper.createRequest(serverReq, true, headerMap);
The createRequest method takes a SipServletRequest instance of the original request, an optional boolean indicating whether the sessions should be linked, and a java.util.Map<String,java.util.Set> map of headers that will be used instead of the headers in the original request. The From and To headers are the keys in the map. The only headers that can be set using this map are non-system headers and the From, To, and Route headers.
See Example 2–6 for the full method where B2buaHelper is used to create a request that links two sessions.