  Recent advancements in wireless technologies towards the next-generation
cellular networks have brought a new era that made it possible to apply
cellular technology on traditionally-wired networks with tighter requirements,
such as industrial networks. The next-generation cellular technologies (e.g.,
5G and Beyond) introduce the concept of ultra-reliable low-latency
communications (URLLC). This thesis presents a Software-Defined Networking
(SDN) architecture with programmable data planes for the next-generation
cellular networks to achieve URLLC. Our design deploys programmable switches
between the cellular core and Radio Access Networks (RAN) to monitor and modify
data traffic at the line speed. We introduce the concept of
\textit{intra-cellular optimization}, a relaxation in cellular networks to
allow pre-authorized in-network devices to communicate without being required
to signal the core network. We also present a control structure, Unified
Control Plane (UCP), containing a novel Ethernet Layer control protocol and an
adapted version of link-state routing information distribution among the
programmable switches. Our implementation uses P4 with an 5G implementation
(Open5Gs) and a UE/RAN simulator. We implement a Python simulator to evaluate
the performance of our system on multi-switch topologies by simulating the
switch behavior. Our evaluation indicates latency reduction up to 2x with
\textit{intra-cellular optimization} compared to the conventional architecture.
We show that our design has a ten-millisecond level of control latency, and
achieves fine-grained network security and monitoring.
