In this article we explore various network layer concepts that play a
crucial role in the design of mobile networking systems. We show that
mobility is essentially an address translation problem and is best res
olved at the network layer. We describe services that must be supporte
d at the network layer to carry out the task of address translation. U
sing these service primitives as building blocks, we describe a networ
k-layer architecture which enables smooth integration of mobile end sy
stems within the existing Internet. A summary of some of the key Mobil
e IP proposals is presented, and it is shown that each proposal can be
viewed as a special case of the architecture outlined in this article
.