The Ricochet MicroCellular Data Network (MCDN) is a packet switched wireless mesh network developed by Metricom, Inc. This network provides virtual serial connections through a wireless modem (AT command compatible). The MCDN wireless backbone is made up of a mesh of routing radios attached to streetlights and buildings. Packets are routed form the wireless modem, through the mesh, and onto Metricom's nationwide wired backbone. From there, the data can be forwarded onto a private LAN, the Internet, or into the telephone system. The Talk will describe the MCDN system in detail, concentrating on the physical, data link, and network layers of the protocol stack.