Protocol and Network Management

Wireless connections today are ubiquitous and taken for granted; however, there is a complex world at work behind the scenes that relies on highly specific conditions. Whether on a laptop, cell phone, or other wireless handheld device, everyone has experienced the frustration of a faulty wireless signal. For this reason, it is helpful to understand some causes of signal weakness or failure. A brief study of the differences between wired and wireless networks, the basics of multiple access protocols, and increased challenges posed by mobility will offer a basic understanding of the complexities involved in successful wireless data transmission, or what can be described as the "21st century grease of the daily grind."

When a user chooses to "unplug" from the wired internet and connect through a virtual wire instead, they introduce a myriad of problems. Some basic challenges result from the differences between a wired and wireless network: decreasing signal strength, interference, and multipath propagation. Signals, which are electromagnetic radiation, attenuate and result in path loss (a weaker transmission) due to interfering matter such as walls or distance in general. Other types of interference include radio sources transmitting at the same frequency, and nearby electromagnetic noise from appliances or motors. The strength of a signal relative to the overall noise interference is the signal-to-noise ratio (SNR). When the SNR is high, the bit error rate (BER) is lowered, resulting in a more reliable transmission. Finally, signal blurring occurs when parts of the electromagnetic wave bounce off objects or the ground. When this happens, the signal is taking paths of many different lengths to reach the receiver, a phenomenon known as multipath propagation. Multipath propagation is complicated further when the objects between sender and receiver are in motion.

Successful wireless networking becomes even more intricate when more than one host needs to transmit across a shared medium. This requires a multiple access protocol, or plan to prevent interference between the many signals trying to reach nearby receivers. Three basic multiple access protocols include channel partitioning, random access, and taking turns. The latter two are somewhat self-explanatory; the first is more interesting to study further. In particular, code division multiple access (CDMA) is a prevalent channel partitioning protocol in which every channel uses the full available spectrum, but is encoded and decoded byway of a "pseudo-random digital sequence" or code. This code is changing at an extremely rapid rate known as the chipping rate -- much faster than the data bits being encoded. This allows each user or channel to be assigned a unique partition of the codespace, thereby preventing multi-host interference. But in the real world of WiFi (the IEEE 802.11 wireless LAN standards), there are often not only multiple hosts, but multiple wireless access points (APs) as well. When a user is able to receive a signal from more than one AP, such as in busy public locations, this spot is known as a WiFi jungle. A WiFi jungle requires each host to employ an algorithm (determined by its specific 802.11 firmware and software), which selects the AP to associate with by way of passive or active scanning. When a user is required to enter a username and password for WiFi access, the chosen AP is requiring authentication before allowing the association; when multiple users are associated with the same AP, the multiple access protocol used by 802.11 WiFi is a random access protocol known as CSMA/CA (carrier sense multiple access with collision avoidance). This protocol operates by requiring