JPL's Wireless Communication Reference Website Chapter: Network Concepts and Standards Section: Data Systems, CDPD

Mobile Data Intermediate System (MDIS)

An MDIS connects to several MDBSs via wire links (e.g., multiple DS0 trunks) or micro waves. The MDIS consists of frame relay switch, packet router and workstation. It receives data from one correspondent network entity and forwards it to another correspondent network entity. The MDIS queues all packets from other intermediate systems (the packets are to be delivered to the M-ESs), and sent them to the corresponding MDBS for transmission on the forward link. The MDBS broadcasts frames in its radio coverage area. Only M-ESs that have valid Network Entity Identifiers (NEIs) can decode the data received.

The MDIS supports user mobility by operating a CDPD-specific Mobile Network Location Protocol to exchange location information of CDPD users.

The MDIS communicates with other intermediate systems by using Connectionless Network Services (CLNS) where every packet (called Network Protocol Data Unit or NPDU) is routed individually based on the destination address of the packet and knowledge of the current network topology. Initially, CDPD provides two CLNSs:

• the standard OSI Connectionless Network Protocol and
• the Internet Protocol

JPL's Wireless Communication Reference Website © Yi-Bing Lin (Author) and Jean-Paul M.G. Linnartz (Ed.), 1996.