Ethernet is a highly scalable and versatile communications technology. It can be deployed in line, tree, tree and branch, star and ring architectures and both IO and peer-to-peer communications are possible.
Like office networks, PROFINET uses Ethernet switches to connect devices. PROFINET switches can be external infrastructure components or integrated switches. In general, the only requirement for Ethernet switches in a PROFINET network is 100 Mbps full duplex transmission. Most Commercial Off-The-Shelf (COTS) switches can work in a PROFINET network. However, there are many factors to consider when selecting a device, such as the installation environment (harsh manufacturing environments) and requirements for specific PROFINET features. The following section on Selecting will give further details.
In addition, specialized ASIC-based switches are now being fitted into many end devices. Both 2 and 4 port versions are available. Onboard 2-port switches allow easy ‘daisy-chaining’ of devices to enable bus-like line networks to be created. Design considerations here include taking into account accumulated switching delays. In linear networks, 10 switches in a line are usually the desirable maximum.
If HMI traffic and data-intensive signals (e.g. vision) are required, it’s worth paying attention to overall bandwidth requirements. PROFINET’s ability to reserve bandwidth for particular functions means that limitations rarely occur. It also means that multiple-functionality can exist on a single network.
For high integrity systems, PROFINET supports media redundancy with ring topologies. If a cable or device fails, then the system automatically segments itself into a ‘line’ topology to keep the rest of the system active.
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