code: public void setOutboundInterface(InetAddress inetAddress) {
  		if(!isValid()) {
  			throw new IllegalStateException("the session has been invalidated");
  		}
  		if(inetAddress == null) {
  			throw new NullPointerException("parameter is null");
  		}
  		String address = inetAddress.getHostAddress();
  		List<SipURI> list = sipFactory.getSipNetworkInterfaceManager().getOutboundInterfaces();
  		SipURI networkInterface = null;
  		for(SipURI networkInterfaceURI : list) {
  			if(networkInterfaceURI.toString().contains(address)) {
  				networkInterface = networkInterfaceURI;
  				break;
  			}
  		}
  
  		if(networkInterface == null) throw new IllegalArgumentException("Network interface for " +
  				address + " not found");
  		try {
  			outboundInterface = new SipURIImpl(SipFactoryImpl.addressFactory.createSipURI(null, address), ModifiableRule.NotModifiable).toString();
  		} catch (ParseException e) {
  			logger.error("couldn't parse the SipURI from USER[" + null
  					+ "] HOST[" + address + "]", e);
  			throw new IllegalArgumentException("Could not create SIP URI user = " + null + " host = " + address);
  		}
  	}
docs: /*
  (non-Javadoc)
  @see javax.servlet.sip.SipSession#setOutboundInterface(java.net.InetAddress)