Flexible Topologies of Sercos III
What is a Topology?
Topology is the name for the networking structure of several devices with each other, which enables data exchange of these devices with each other. The special topology of a network determines its reliability: the functionality of the entire system in case of failure of individual components only remains intact with alternate/redundant connections between the components. With this, the physical topology describes the structure of the connections and the logical topology describes the data flow in the connections.
What are flexible topologies of Sercos III?
All Sercos networks are generally composed of at least one master for coordination and a slave for execution of the automation functions. They are arranged simply and clearly in a line or ring topology. This is done without switches or hubs, which leads to enormous cost savings.
With this, each device has at least two Ethernet connections. These are connected via CAT5e Ethernet cables with the other devices.
With this, Sercos III does not use the star topology of the Ethernet.
1. Line Topology
With the line topology (also called linear topology or bus topology), all devices are arranged in series. The master is always at the beginning of the line. Differing from this, in certain cases it also can be located between two lines. The data passes through all slaves, which are connected in series, i.e. one behind the other, and it is directed back from the last device (the so-called loop-back). Independent of the line sequence, all data is guaranteed to reach each participant at least once in a cycle, as all components of the system evaluate the data in two directions.
The advantage of this method is the very easy and cost-efficient networking of all devices with each other, even over long distances (for example with assembly lines).
The disadvantage of this topology is that a failure in one transfer segment is immediately felt in the entire system.
The line topology is used mostly in large production installations and also for connecting production cells.
2. Ring Topology
With additional cables, the network can be connected to a ring. With one line, this works with just one cable between the master and the last slave, with two lines between the two last slaves each. With the ring topology, the master sends data into the ring from both ports, so that these are also evaluated in the ring in two flow directions.
With the flexible topologies of Sercos III, this is not a single ring, but a double ring structure. With this, in each case all components are connected with each other via two connections. Only this interconnection enables a further functionality of the network even with failure of individual connections.
The first advantage of the flexible topologies of Sercos III is the redundant wiring, which enables trouble-free operation and reports faults for repair. Faults can then be repaired without impairment of the system. The network thus always remains available, even in the case of a wire break. Furthermore, each component of the ring topology operates as an amplifier, all components have the same access possibilities, the transmission bandwidth is guaranteed and programming is easy because this is a regular topology.
The disadvantages of the flexible topologies of Sercos III are the relative wiring expenditure, the relatively high diameter of the system and the fact that data transmissions can be intercepted easily.
Ring Redundancy and Hot-plugging
In case of a fault (for example a wire break), the flexible topologies of Sercos III use the ring redundancy. With this, the ability to communicate remains fully intact by quick switching of the transmission path, as the active ring is divided into two lines. With this, the real-time data are transmitted redundant, i.e. on two separate paths (the so-called primary and secondary channel) during normal operation. In case of a fault, the nodes directly on the fault location switch within max. 25 μs from “transfer” to “loop-back”. As the ability to communicate remains even with a wire break, new participants (hot-plugging) or new participant groups (hot-swapping) can also be fitted or connected to the communication network.
3. Other Topologies:
Other possible flexible topologies of Sercos III are hierarchical, cascaded network structures. With this, individual network segments are networked with each other via a ring or line topology.
The advantages of this networking are synchronized network structures coupled in real-time, as well as the ability to generate different cycle times in the individual segments, for example by networking of drives and controls. Furthermore, all participants of the network can communicate with each other in real-time.
The infrastructure component Topo Extension offers new options here for simple wiring of flexible topologies of Sercos III, as it reduces the wiring expenditure considerably. This is done by the device first combining the two required lines of the ring wiring to one cable and then dividing the signals again to two individual cables. In this way, individual components can be connected with a single cable while maintaining the advantages of the flexible topologies of Sercos III.
Installation of the flexible Topologies of Sercos III
The installation of a flexible topology of Sercos III is simple and requires no special network configuration. All devices are connected by patch or cross-over cables with each other. The Ethernet ports of the devices are interchangeable and can also be used to connect standard Ethernet devices (for example notebooks) to a SERCOS III real-time network. In this way, any Ethernet and IP protocols can be used to access devices without influencing the real-time behavior of the SERCOS III network or even having to activate the Sercos III protocol.
The max. number of participants per ring/line for the flexible topologies of Sercos III is 511 participants. Only 254 participants per ring are possible for Sercos I and Sercos II.