The short answer is that there are many networking options for PC-based controls, not all that dissimilar to non-PC-based controls. A good number of them are based on the Ethernet protocol as that is the most common networking protocol for PCs.
PC-based controls have become more common in industrial settings as they have steadily displaced mainstays like PLCs. Desirable features include openness with regards to networking, which allows for greater connectivity. Other reasons include the ease of integrating a control system with other PC functions including connecting with HMIs, data gathering and processing, and the ability to connect with higher-level, enterprise-wide IT systems.
One of the most common networks is Ethernet/IP. The IP stands for industrial protocol and it is essentially an industrial application layer protocol operating over the Ethernet medium. It also combines the CIP Motion application layer, a feature that ensures determinism that enables synchronized multi-axis motion control.
Another option is EtherCAT, which is short for Ethernet for Control Automation Technology. Perhaps the most important point about EtherCAT is the distributed clock technique it uses allowing axes to be synchronized with less than 1 usec of jitter. Developed by Beckhoff Automation, the protocol delivers fast throughput because hardware processes messages before forwarding to the next node. Each node reads data relevant only to it as the data frame passes, and inserts new data into that data stream on the fly.
The PCI bus is an option for PC-based controls as well. Because PC-based systems were the first ones to use motion control cards that were PCI-based, the PCI-bus card was one of the original and still is fairly common throughout the industry. PROFINET is another viable option, with manufacturers such as Siemens offering PC-based controllers using the network, which is also based on Ethernet.