 7 active or up to 255 inactive (parked) slave devices. Point of Attachment (POA): A point of attachment is a generic point at which wireless device connects to a wireless network. Wi-Fi access points and WiMAX or 3GPP cellular base stations are all examples of points of attachment. Point of presence (POP): A point of presence (POP) is an access point into the Internet. An ISP or other online service provider will have one or more POPs to carry customer traffic onto the Internet. Chapter Sixteen Point to Point Transport Protocol (PPTP): A protocol that allows secure transmission of data over virtual private networks (VPN) that make use of insecure connections such as the public telephone system or the Internet. Processing Gain: Processing gain is achieved when a chipping code is used to spread a bit stream into a wider bandwidth chip stream. The pro- cessing gain in decibels is equal to 10 logio(C) where C is the length of the chipping code. Protocol: A standard set of rules, or language, for enabling network com- munication between devices. Examples of protocols include HTTP, FTP, TCP and IP. Quadrature Phase Shift Keying (QPSK): A modulation technique in which an input data symbol is represented by one of four phase states of the carrier wave. Receiver Sensitivity: The receiver sensitivity is a measure in dBm of the weakest signal that a receiver can reliably decode at a specified bit error rate (BER). Receiver sensitivity is a function of the modulation method used, since more complex schemes, such as 16- or 64-QAM, require a higher received signal strength for reliable decoding. Typically, decoding 64-QAM requires 15-20 dB higher signal strength than decoding BPSK. Request for Comments (RFC): A publication by an industry body requesting comments on a proposal relating to standards or generic solutions to a technical problem. The Network Working Group publishes some of the seminal RFCs that established the fundamentals of much of the networking and Internet technology described in this book. Some important exa