Trading CDPD Availability and Voice Blocking Probability in Cellular Networks

48 ellular digital packet data (CDPD) [1–3] networks provide wireless data communications services to mobile users by sharing the radio equipment and unused RF channels with Advanced Mobile Phone System (AMPS) networks [6]. Basically, CDPD transmits packet data over idle AMPS channels, and autonomously switches to another channel when the current channel is about to be assigned for voice usage. CDPD may serve as the wireless extension to other data networks (e.g., Internet) or public switched telephone networks. It supports connectionless network services where every packet is routed individually based on the destination address of the packet and knowledge of the current network topology. Figure 1 illustrates the CDPD network architecture. A CDPD user communicates with the CDPD network using the mobile end system (M-ES). The physical location of M-ESs may change from time to time, but continuous network access is maintained. The mobile data base station (MDBS) is responsible for detailed control of the radio interface, such as radio channel allocation, interoperation with cellular voice channel usage, and radio media access control. In order to share radio resources with the cellular system, MDBSs are expected to be collocated with voice equipment (i.e., AMPS base stations, BSs) that provide cellular telephone service. Furthermore, MDBSs may share cellular equipment (such as antennas for transmitters and receivers) to communicate with the M-ESs. The mobile data intermediate system (MD-IS) connects to several MDBSs via wired links (e.g., multiple DS0 trunks) or microwaves. The MD-ISs support user mobility by exchanging user location information (using the mobile network location protocol) with each other and routing the incoming data frames to destinations based on the user location information. Two distinct routing functions are performed by the MD-IS: the mobile home function and mobile serving function, which are similar to the functionalities of the home and visitor location registers [5] in the cellular network. The intermediate system (IS) enables the CDPD network to communicate with other data networks (e.g., Internet). ISs support the network-layer functionality, and route Connectionless Network Protocol datagrams between MD-ISs and Internet Protocol datagrams between MD-ISs and fixed end systems (F-ESs). An M-ES communicates with an MDBS through a 19.2 kb/s raw duplex wireless link (referred to as a CDPD channel stream). A CDPD channel stream can be shared by several MESs. The link from the MDBS to the M-ESs is called the forward link, and the link from the M-ESs to the MDBS is called the reverse link. When a frame arrives at an MD-IS, the frame is queued in a buffer and sent to the destination MDBS. The MDBS then broadcasts this frame on the forward link. All MESs in the MDBS radio coverage area listen to the broadcast frame. Only the M-ESs with valid identifiers can decode the data. It is clear that the transmission on the forward link is broadcast contentionless delivery. Trading CDPD Availability and Voice Blocking Probability in Cellular Networks