  Wireless Sensor Networks (WSNs) are comprised of thousands of sensor nodes,
with restricted energy, that co-operate to accomplish a sensing task. Various
routing Protocols are designed for transmission in WSNs. In this paper, we
proposed a hybrid routing protocol: Zonal-Stable Election Protocol (Z-SEP) for
heterogeneous WSNs. In this protocol, some nodes transmit data directly to base
station while some use clustering technique to send data to base station as in
SEP. We implemented Z-SEP and compared it with traditional Low Energy adaptive
clustering hierarchy (LEACH) and SEP. Simulation results showed that Z-SEP
enhanced the stability period and throughput than existing protocols like LEACH
and SEP.
