JPL's Wireless Communication Reference Website

Chapter: Network Concepts and Standards
Section: Data Systems, CDPD


CDPD Roaming Management

Contributed by Yi-Bing Lin

The CDPD roaming management is achieved by two functions: the Mobile Home Function (MHF) and the Mobile Serving Function (MSF). An M-ES is identified by a distinct Network Entity Identifier (NEI). Every NEI is associated with a home MDIS. The home MDIS maintains a Location Directory to record the address of the current serving MDIS for each of its homed M-ESs (this procedure is referred to as the Location Directory Service). The M-ES may roam away from its home MDIS and visit other MDIS. The visited MDIS maintains a Registration Directory to keep track of all visiting M-ESs (this procedure is referred to as the Registration Directory Service in the MHF).

Location Registration

The CDPD location registration procedure is described in the following steps:


Step 1:

From the channel stream, an M-ES identifies its location (the address of the serving MDIS). When the M-ES moves to another serving area, it registers at the Registration Directory of the current serving MDIS (the Registration Service in the MSF).

Step 2:

The serving MDIS then notifies the home MDIS of the current location of the M-ES, and the Location Directory of the home MDIS is updated (the Registration Service in the MHF).

Step 3:

The home MDIS then sends a message to the old serving MDIS to delete the M-ES record of the Registration Directory of the old MDIS.

NPDU Forwarding

Packet forwarding or Network Protocol Data Unit (NPDU) forwarding is described in the following steps:


Step 1:

To route an NPDU from the originating MDIS to an M-ES, the NPDU is first routed to the home MDIS according to the NEI of the M-ES.

Step 2:

If the M-ES is not in the home area, then the address of the current serving MDIS of the M-ES is identified in the Location Directory. The NPDU is then encapsulated and tunneled to the current serving MDIS. This procedure is referred to as the Redirection and Forwarding Service in MHF at the home MDIS.

Step 3:

Upon the receipt of the forwarded NPDU, the current serving MDIS decapsulates the NPDU and routes it to the cell where the M-ES resides. This process is referred to as the Readdress Service in MSF at the serving MDIS).



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