When the M-ES moves from a cell within one routing area subdomain to a cell in a different routing area subdomain (illustrated in Figure 4.14), the above intra-area cell transfer mechanism is insufficient. In this instance, the data link end-points are no longer valid. On the movement from one routing area subdomain to another, the serving MD-IS has changed. This means that a new data link must be established between the M-ES and the new serving MD-IS. The re-establishment of the data link, and the associated administrative authentication functions must be performed for this type of movement.
On sensing that relocation has occurred from one routing area subdomain to another routing area subdomain4.12 , the M-ES initiates establishment of a data link4.13 . Once the data link is established, the M-ES must register its address (or addresses4.14 ). This is necessary since the new serving MD-IS is unaware of the active network addresses at the M-ES. The M-ES must execute the normal registration process involving ESH, RDR, RDC and ISC messages as outlined in Section 4.8.
On successful re-registration of the M-ES at the new serving MD-IS, the Location Directory at the home MD-IS is updated. The update reflects the fact that any future network data packets received destined for the mobile unit's NEI are now redirected toward the new serving MD-IS. The protocol events are illustrated in Figure 4.15.
