private static StringBuffer buildNetworkInterfaceDescriptor() {
		Enumeration e1;
		try {
			e1 = NetworkInterface.getNetworkInterfaces();
		} catch (Throwable t) {
			// not available
			return null;
		}
		StringBuffer b = new StringBuffer();
		while (e1.hasMoreElements()) {
			NetworkInterface ni = (NetworkInterface) e1.nextElement();
			StringBuffer b1 = getMACAddressDescriptor(ni);
			StringBuffer b2 = getInetAddressDescriptor(ni);
			StringBuffer b3 = new StringBuffer();
			if (b1 != null) {
				b3.append(b1);
			}
			if (b2 != null) {
				if (b3.length() > 0) {
					b3.append('=');
				}
				b3.append(b2);
			}
			if (b3.length() > 0) {
				if (b.length() > 0) {
					b.append(';');
				}
				b.append(b3);
			}
		}
		return b;
	}