The supply chains for today's technology giants are fantastically complex — yet it's often true that the most essential and irreplaceable components come from a small number of countries. Here's a look at some key components of the Chinese networking giant Huawei and how suppliers have responded to Washington's ban on sales of US technology to the company. The ban, which also includes components from other countries that contain significant US technology or materials, has quickly gone global, threatening Huawei's survival.