center of each bit, where an example of transition can be a rising edge. Transition in the opposite direction is used to represent logic 0. Physical layer also determines the utilization of media during data transmission based on signaling. When using "base band signaling" all available frequencies (the entire bandwidth) is used for data transmission. Ethernet mostly uses base band signaling. When working with "broadband signaling" only one frequency (part of the entire bandwidth) is used, with multiple signals transmitted simultaneously over the same media. The most popular example of broadband signaling is TV signals, where mul- tiple channels working on different frequencies are transmitted simultaneously. Physical layer also determines the topology of the network. The network can have bus, star, ring, or mesh topology and the implementation can be performed with LAN or WAN specifications. The physical layer should ensure efficient shar- ing of the communication media among multiple devices with proper flow control and collision resolution. Some examples of physical layer protocols are: CSMA/CD (carrier sense multiple access/collision detection), DSL (digital subscriber line) and RS-232. The physical layer is special compared to the other layers of the OSI model in having both hardware and software components that makeup this layer. There can be sublayers associated with the physical layer. These sublayers further break the functionality performed by the physical layer. 10.3 Data Link Layer This is the second layer (L2) in the ISO/OSI model. It is divided into two sublayers, the logical link control (LLC) and media access control (MAC) on IEEE 802 local area networks, and some non-IEEE 802 networks such as FDDI. LLC is the upper Fundamentals of EMS, NMS and OSS/BSS sublayer and handles functions for control and establishment of connection for logical links between devices in the network. MAC is the lower sublayer in the data link layer (DLL) and handles functions that control access to the network media like c