【正文】 iple access control (MAC) layer needs to minimize collisions, allow fair access, and semireliably transport data over the shared wireless links in the presence of rapid changes and hidden or exposed terminals. The work layer needs to determine and distribute information used to calculate paths in a way that maintains efficiency when links change often and bandwidth is at a premium. It’s also needs to integrate smoothly with traditional, non ad hocaware interworks and perform functions such as autoconfiguration in this changing environment. The transport layer must be able to handle delay and packet loss statistics that are very different than wired works. Finally, applications need to be designed to handle frequent disconnection and reconnection with peer applications as well as widely varying delay and packet loss characteristics. Ad hoc works are suited for use in situations where infrastructure is either not available, not trusted, or should not be relied on in times of emergency. A few examples include: military solders in the field。 sensors scattered throughout a city for biological detection。 the forestry or lumber industry。 space exploration。 and temporary offices such as campaign headquarters. History The history of ad hoc works can be traced back to 1972 and the DoDsponsored Packet Radio Network (PRNET), which evolved into the Survivable Adaptive Radio Networks(SURAN) program in the early 1980s [l]. The goal of these programs was to provide packetswitched working to mobile battlefield elements in an infrastructureless, hostile environment (soldiers, tanks, aircraft, etc., forming the 3 nodes in the work). In the early 1990s a spate of new developments signaled a new phase in ad hoc working. Notebook puters became popular, as did opensource software, and viable munications equipment based on RF and infrared. The idea of an infrstructureless collection of mobile hosts was proposed in two conference papers [2,3], and the IEEE submittee adopted the term “ad hoc works.” The concept of mercial (nonmilitary) ad hoc working had arrived. Other novel nonmilitary possibilities were suggested (as mentioned in the introduction), and interest grew. At around the same time, the DoD continued from where it left off, funding programs such as the Global Mobile Information Systems(GloMo), and the Nearterm Digital Radio(NTDR). The goal of GloMo was to provide officeenvironment Ethertype multimedia connectivity anytime, anywhere, in handheld devices. Channel access approaches were now in the CSMA/CA and TDMA molds, and several novel routing and topology control schemes were developed. The NTDR used clustering and linkstate routing, and selforganized into a twotier ad hoc work. Now used by the US Army,NTDR is the only “real” (nonprototypical) ad hoc work in use today. Spurred by the growing interest in ad hoc working, a number of standards activities and mercial standards evolved in the mid to late’ the IETF, the Mobile Ad hoc Networking(MANET) working group was horn, and sought to standardize routing protocols for ad hoc works. The development of routing within the MANET working group and the larger munity forked into reactive (routes ondemand) and proactive (routes readytouse) routing protocols [4]. The submittee standardized a medium access protocol that was based on collision avoidance and tolerated hidden terminals, making it usable, if not optimal,for building mobile ad hoc work prototypes out of notebooks and PCMCIA and Bluetoot