code: public void setOutboundInterface(SipURI outboundInterface) {
  		if(!isValid()) {
  			throw new IllegalStateException("the session has been invalidated");
  		}
  		if(outboundInterface == null) {
  			throw new NullPointerException("parameter is null");
  		}
  		List<SipURI> list = sipFactory.getSipNetworkInterfaceManager().getOutboundInterfaces();
  		SipURI networkInterface = null;
  		for(SipURI networkInterfaceURI : list) {
  			if(networkInterfaceURI.equals(outboundInterface)) {
  				networkInterface = networkInterfaceURI;
  				break;
  			}
  		}
  
  		if(networkInterface == null) throw new IllegalArgumentException("Network interface for " +
  				outboundInterface + " not found");
  		this.outboundInterface = outboundInterface.toString();
  		if(outboundInterface.getTransportParam() != null) {
  			this.transport = outboundInterface.getTransportParam();
  		}
  	}
docs: /*
  (non-Javadoc)
  @see org.mobicents.javax.servlet.sip.SipSessionExt#setOutboundInterface(javax.servlet.sip.SipURI)