58 CHAPTER 4 Wireless Networking Direct sequence spread spectrum (DSSS) DSSS works by dividing the data and simultaneously transmitting on as many frequencies as possible within a particular frequency band (also known as a channel). DSSS adds redundant bits of data known as chips to the data to represent binary 0s or 1s. The ratio of chips-to-data is known as the spreading ratio: the higher the ratio, the more immune to interference the signal is, because if part of the transmission is corrupted, the data can still be recovered from the remaining part of the chipping code. Additionally, DSSS protects against data loss through the redundant, simultaneous transmission of data. WIRELESS NETWORK ARCHITECTURE Wireless networks operate at the physical and data link layers of the open sys- tem interconnection (OSI) model. Both FHSS and DSSS are implemented at the physical layer of the OSI model. The data link layer is divided into two sublayers: the media access control (MAC) and logical link control (LLC) layers. The MAC layer is responsible for such things as framing data, error control, syn- chronization, and collision detection and avoidance. Wireless networks utilize carrier sense multiple access with collision avoidance (CSMA/CA) method for protecting against data loss. Using CSMA/CA, a wireless workstation first tries to