  Understanding the real achievable performance of mobile ad hoc networks
(MANETs) under practical network constraints is of great importance for their
applications in future highly heterogeneous wireless network environments. This
paper explores, for the first time, the performance modeling for MANETs under a
general limited buffer constraint, where each network node maintains a limited
source buffer of size $B_s$ to store its locally generated packets and also a
limited shared relay buffer of size $B_r$ to store relay packets for other
nodes. Based on the Queuing theory and birth-death chain theory, we first
develop a general theoretical framework to fully depict the source/relay buffer
occupancy process in such a MANET, which applies to any distributed MAC
protocol and any mobility model that leads to the uniform distribution of
nodes' locations in steady state. With the help of this framework, we then
derive the exact expressions of several key network performance metrics,
including achievable throughput, throughput capacity, and expected end-to-end
delay. We further conduct case studies under two network scenarios and provide
the corresponding theoretical/simulation results to demonstrate the application
as well as the efficiency of our theoretical framework. Finally, we present
extensive numerical results to illustrate the impacts of buffer constraint on
the performance of a buffer-limited MANET.
