 by the Web server. hub A device that extends the maximum physical length of a network by cleaning and retrans- mitting signals among network segments. A hub provides the central connecting point in a star network topology. Also called a multiport repeater. Huffman encoding A statistical encoding technique for lossless compression. Statistical encoding is an entropy-encoding method. The Huffman algorithm calculates the frequency of occurrence of each octet for a given portion of the data stream. It then determines the minimum number of bits to allocate to each character and assigns an optimal code accordingly. The codes are stored in a codebook. This technique is used in sound, still, and moving image compression. hybrid circuit A circuit that has four sets of terminals arranged in two pairs designed so that there is high loss between the two sets of terminals of a pair when the terminals of the other pair are suitably terminated. Hybrid circuits are commonly used to couple four-wire circuits to two- wire circuits. hybrid network A network composed of both public and private facilities. Hz (Hertz) A unit of electromagnetic frequency that is equal to one cycle per second. IAD (integrated access device) A device that consolidates voice, data, Internet, and video services using DSL, ATM, TDM, or MGCP over T-1/E-1 lines. The IAD, installed on the end-user's site, is a form of CPE. IANA (Internet Assigned Numbers Authority) An organization that oversees addresses and top-level domain name allocations. iBurst An Australian WMAN technology that provides mobile wireless broadband Internet access. iBurst is a pure IP, end-to-end system. ICANN (Internet Corporation for Assigned Names and Numbers) A nonprofit cor- poration that manages the domain name and root server systems. ICMP (Internet Control Message Protocol) An integral part of IP that handles error and control messages. Routers and hosts use ICMP to send reports of problems about datagrams back to the original sources that sent the datagrams. ICMP also includes an 