In this section we'll begin ascending the OSI reference model from the very bottom rung: the physical layer. Layer 1 is the "dumbest" layer, but that doesn't mean it's not important! We also begin at the bottom since things are much simpler at the lower layers. Layer 1 is where signals get passed around. These signals pass across conductors in the form of wires and connectors. Wires in the form of cables, come in a large assortment, which can be classified into two basic types: cheap and easy or expensive and difficult. Easy and difficult refer to the ease or difficulty of working with a particular media. On the cheaper and easier end, we have twisted pair. It's certainly inexpensive and relatively easy to work with, but it's also the least secure media. The most secure in terms of being relatively immune to interference and eavesdropping is fiber optic media, but it comes at a much higher cost and is more difficult to install. Security requirements for a project must be weighed against cost. A higher-cost solution may be warranted if security is a firm requirement of the installation. Devices that work at the physical layer are hubs - both passive and active. There are also devices that span several layers beginning at layer 1 such as a NIC. Though not devices, the wires, connectors, and cables we just mentioned are materials that exist completely within the physical layer. For the CISSP exam, topics such as network topologies and cable specs are not too important. What is important at layer 1, however, are the security threats it faces. These include tapping, data sniffing, equipment and media theft, vandalism, electromagnetic interference, unauthorized access, and data emanation.