This paper is concerned with a novel two-tier handoff scheme for mobile communications in a hierarchical NEMO (Network Mobility) system, composed of access routers (ARs), mobile routers (MRs), and visiting mobile nodes (MNs). In the proposed two-tier handoff scheme, the service areas of MR and AR are divided into handoff and non-handoff regions, respectively. Concurrent voice/data sessions in a hierarchical AR-MR model are classified according to the locations of MN and MR within the corresponding MR?s and AR?s service areas. An analytical model with 4-D Markov chains is built to analyze the multimedia communications in terms of the system utilization and the blocking probabilities of new sessions and handoff sessions. Analytical results show that the influences of the residence time of MN and MR on the handoff blocking probability can be very significant. The size of MR?s and AR?s service areas on the system performance is also investigated. Index Terms-Channel allocations, Mobile routers, Handoff, Makov chains, NEMO, and Mobile communications.