专利名称：Protocol for packet data communication
system
发明人：Tymes, LaRoy,Ennis, Gregory B.申请号：EP94105048.6申请日：19940330公开号：EP0619662A3公开日：19951102
摘要：A packet data transmission system is used to link a number of remote hand-held data-gathering units such as bar code readers to a central computer. Data packetsare sent from the remote units by a spread spectrum RF link to intermediate basestations, then sent by the base stations to the central computer by a serial link. Theremote hand-held units initiate an RF exchange to and from the base stations, receivingonly during a time window following a transmission from the remote unit. The basestations cannot initiate an exchange with the remote units, but instead send data to theremote units only as part of the exchange. To alert a remote unit when a message iswaiting at a base station to be sent to a particular unit, some of the acknowledge (base-to-remote) packets sent by the base station may contain an identification such as a list ofall remote units (identified by ID number) which have messages waiting. Alternatively, abit map can be used to identify these remotes. These base-to-remote packets with theidentification of remotes with messages waiting are called \"announcements.\" Each remoteunit (if not engaged in regular exchanges for a time interval) periodically listens (activatesits receiver) to receive an announcement packet containing such a list or bit map anddecodes this announcement to see if it has a message waiting. If so, this remote unit then
sends a transmit packet so the base can send the waiting message in an acknowledgepacket.
申请人：SYMBOL TECHNOLOGIES, INC.
地址：116 Wilbur Place Bohemia New York 11716 US
国籍：US
代理机构：Wagner, Karl H., Dipl.-Ing.
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