code: public void putTransaction(SipServletRequestImpl request) {
              final String txId = ((ViaHeader) request.getMessage().getHeader(ViaHeader.NAME)).getBranch();
              final TransactionApplicationData txData = request.getTransactionApplicationData();
              if(txData != null && this.transactionMap.put(txId, txData) == null) {
                      if(logger.isDebugEnabled()) {
                              logger.debug("Transaction "+txId+" added to proxy.");
                      }
              }                               
      }
docs: https://code.google.com/p/sipservlets/issues/detail?id=238