Communication Protocols - Essay Example

COMMUNICATION PROTOCOLS Student’s Name Institution Communication Protocols Comparing and Contrasting Modbus, TCP/IP and other Common Industrial Control Protocols with each Other The Modbus protocol refers to a messaging structure which was developed in 1979 by Modicon. In essence, Modbus can typically be used to refer to one of the 3 linked protocols namely the Modbus RTU, the Modbus ASCII and the Modbus TCP/IP. The “Modbus ASCII” unlike the other two can be regarded as being the first Modbus which is also still a serial protocol and which runs typically on either the “RS-485” Physical layer or the “RS-232” physical layer. The Modbus ASCII frame is known to be about 252 bytes in its length and it is also capable of having a total of about 247 addresses. The function codes and the message frame of the Modbus ASCII are usually very simple. On the other hand, as opposed to the Modbus ASCII Protocol, the Modbus RTU is actually its small variation and the only difference between them is in the data encoding. This is because while the Modbus ASCII is ascertained though it encoding of the message using the ASCII characters, the Modbus RTU on the other side is known to use the bytes and thus enhancing or increasing the throughput of the protocol. Generally, the use of the Modbus RTU is more popular especially in new installations (Merz, et al, 2009). Unlike the Modbus ASCII and the Modbus RTU protocols, the Modbus TCP/IP Protocol was only added much later on. Indeed, in order to better think about the Modbus TCP/IP protocol is for it to be simply depicted as being an encapsulation of a packet of the Modbus RTU in a TCP/IP Packet. Despite the fact that there can be more to it than can be seen, that is what the Modbus actually did. Due to this fact, it can be genuinely ascertained that it is both simple and easier to implement the Modbus TCP/IP protocol. However, the trade off of using this protocol (The TCP/IP Protocol) is normally slow as compared to the other two protocols due to the fact that it utilizes the TCP/IP Protocol in disseminating all the messages. The Modbus Protocol is therefore used in the establishment of the master-slave and client server communication which happens between the intelligent devices. In addition to that, it is a de-facto standard that is known not only to be genuinely open but also a network protocol that is used widely in the environment of industrial manufacturing. The Modbus Protocol has been implemented and used by numerous vendors on a variety of devices in order to transfer I/O/ Analog/discrete data and also register the data between the different control devices. Moreover, the Modbus Protocol is used as a common denominator or a lingua franca between different manufacturers. In Europe and North America alone, approximately 7 million nodes of Modbus have been reported by analysts in the industry. The application or use of the Modbus protocol is in “multiple master-slaves” applications in the programming and monitoring of the devices and in the communication between the sensors, instruments and intelligent devices. Modbus is also used in the monitoring of the field devices using both the HMIs and the PCs. The Modbus protocol can ideally be used in the RTU applications especially where there is need for wireless communication. As a result, the Modbus protocol is normally used in innumerable oil and gas substation applications. However, it should be noted by all and sundry that Modbus cannot be regarded as being an industrial protocol. This is attributed to the fact that infrastructure, building, energy and transportation applications also use the benefits that are attributed to the Modbus protocol. On the other hand, unlike the Modbus, the Modbus TCP/IP Protocol refers to a common internet transport protocol comprising of a set of “layered protocols” which present a reliable mechanism of data transport between two machines. Indeed, the use of the Ethernet has now become a de facto standard in the contemporary world of corporate enterprise systems and therefore it is not amazing that it has now established itself as being the de facto standard in factory networking. It should be noted that in fact, the use of Ethernet is not a new technology since it has matured to an extent that the cost of implementing it has significantly dropped. Unlike the Modbus protocol, the use of the “Ethernet TCP/IP” is in the factory in which it is used in allowing genuine integration with the MES and Corporate Intranet systems which support the factory. It should be observed that the use of an open “Modbus TCP/IP” protocol was initiated in the year 1999 in order to move the Modbus protocol into the 21st century. It should be noted that Modbus is therefore the combination of the scalable, versatile and even ubiquitous Ethernet’s physical network with both a representation of data that is vendor-neutral and a networking standard that is universal (Chowdhury, & Crossley, 2009). Just like Modbus can be regarded as being the grandfather of all the known protocols, “Profibus” can be regarded as being its young athlete. Designed in the 1990’s, it was aimed at meeting all the needs of communication for the factory and for the automation process. And just like the Modbus protocol, the Profibus protocol uses numerous terms which are associated with it; for instance, Profibus PA, Profibus DP, Profidrive, Profisafe and Profinet. Just like the Modbus Protocol, the Profibus protocol also uses a “master slave type protocol” but however, it has got an additional token ring protocol that allows for multiple users. In addition to that, unlike the Modbus protocol, devices in the Profibus protocol are known to undergo a start up sequence in which they join or get linked to the network. In such a situation, each slave on the network is known actually maintains or retains a “failsafe timer”. As a result, if the master doesn’t communicate to it within a specific time limit, then it is definite that the slave will go into a safe status and thus the master has to once more undergo the start up process before any further exchange of data can occur. This will normally happen in combination or together with a “watchdog timer” located in the master that ensures that all occurring communication is done in each bus cycle and within the specific time values. Despite the fact that Profinet was just built or designed on the same principle like Profibus, it should be noted that unlike the Modbus protocol which asserted the “Modbus RTU packet” and combined it to become the “TCP/IP Packet”, Profinet was actually designed with an aim of taking advantage of the use of the Ethernet and to also make it easier to permit the easy or simple addition of any other higher end functions of Profibus like the Profisafe. One of the similarities between the Profibus DP and the Modbus is that they are all based on the RS-485 communication protocol. However, it should be noted that there is some small differences because in the Profibus bus, the specification does not just refer to the RS-485 specification that exists but instead, it also extends it to the specification of the RS-485 (Powell & Vandelinder, 2013). One of the notable differences between the Modbus Communication Protocol and the Profibus Protocol is that while the Modbus communication protocol is notable because each device’s diagnostics and data are totally individualized and therefore they must just be adapted, this is not the case in the Profibus Communication protocol. It is prudent to note that despite the fact that both Profinet and the Profibus DP have time constraints which are too tight; various vendors have been able to design a number of modems like the wireless, phone lines and the cell phones which are capable of working well with all of them In conclusion, it should be noted that indeed, despite the fact that Modbus can be regarded as being an easy to use, simple and a modern protocol that is friendly, there is some variation not only in the use of the protocol alone but also in the multi-vendor applications as well thus leading to the creation of problems/complexities in the multi-vendor applications. On the other hand, Profibus can be regarded as being a robust protocol that was designed or created with an aim of automating all the plants. This is because it (the Profibus) works extremely well in numerous multi-vendor environments and it has detailed diagnostics in modems. Modbus communication protocol can come in handy and as an easier option in situations where there is need of connecting or linking a controller to one particular smart device in one remote site or in a “point to point” configuration. However, in circumstances where there is the involvement of different vendors or where there is the involvement of more points and in hazardous environments, then Profibus will definitely emerge as a better solution. The biggest similarity between all the types of protocols listed above is that they are communication protocols that are used in different circumstances which are deemed to be viable. References Chowdhury, S., & Crossley, P. (2009). Microgrids and active distribution networks. New York: Institution of Engineering and Technology. Merz, H, et al. (2009). Building automation: Communication systems with EIB/KNX, LON and BACnet. New York: Springer. Powell, J., & Vandelinder, H. (2013). Catching the process fieldbus: An introduction to PROFIBUS for process automation. New York: Momentum Press. Read More