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About UDP and TCP protocl between simotion and PLC?

Created by: llsl0304 at: 4/16/2008 9:51 AM (4 Replies)

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4/16/2008 9:51 AM	Rate (0)
llsl0304 Posts: 78 Rating: (0)	hello, everyone anyone know the differnt, UDP and TCP? which is better? cycle is shorter? if UDP is better, what way to prove it intuitionisticly? thank you in advance
llsl0304 Posts: 78 Rating: (0)
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4/16/2008 10:31 AM	Rate (0)
aikona Posts: 487 Rating: (36)	Hi From the PLC side : not all communication cards do UDP and TCP ( A mention in the doc like TCP/IP does not mean that it can be used to communicate via TCP.) UDP and TCP : you use send /receive FC's . but UDP : does not give a "reply" .Meaning you send something but you don't know if it has arrived.You have to do your own error routine's .UDP is the fastest TCP : does give a error code if the message has not arrived. My knowledge of simotion is zero but if speed is essential should you not look at using profinet ? Being to Siemens products I presume that comms via S7 could also be possible. Greetings Eric
aikona Posts: 487 Rating: (36)
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4/16/2008 10:45 AM	Rate (0)
dchartier Grandmaster Joined: 9/27/2006 Last visit: 11/22/2024 Posts: 12297 Rating: (2691)	Hello; I am not an IT expert, so this answer only engages me; anyone feel free to correct or expand on what I am saying here. UDP and TCP are both protocols that are installed over IP; they use the sam addressing scheme, and are used tosend packets of data over the Internet between communication partners. TCP is used to establish robust and reliable connection over the Internet; it provides flow control by acknowledging reciept of all packets by the reciever, so the sender is aware of the status of all exchanges. TCP can be full duplex. UDP does not acknowledge reciept of the packet, so the sender is not aware of the status of the transmission. If some packets are missing, there is no inbuilt mechanism to retransmit. UDP has therefore less "overhead" (software to communicate between the sender and the reciever), it is faster asnd simpler. But it is not garanteed. SNMP and DNS are two commonprotocols that use UDP-they don't care much is every single packet sentis recieved, the reciever application will request a new transmission if it needs it. so you, as a programmer, have to decide what is more important to you: security or overall speed. Here is a link to a mode detailed explanation on the subject: http://www.laynetworks.com/Comparative%20analysis_TCP%20Vs%20UDP.htm You should also look at Wikipedia, they generally have very good contributors whocan give you great basic info. Hope this helps, Daniel Chartier

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4/17/2008 9:00 AM	Rate (0)
Manfred Experienced Member Joined: 6/22/2006 Last visit: 3/7/2022 Posts: 156 Rating: (17)	Hi, for a detailed description about UDP and TCP/IP with SIMOTION please have a look to following SIMOTION documents on the documentation CD - \2_Description_of_system_and_functions\Communication.pdf - \2_Description_of_system_and_functions\Basic_TechnologyFct.pdf or to the Online help. You can also find the SIMOTION documents in the Internet: http://support.automation.siemens.com/WW/view/en/10805436/133300 Filter settings: Manuals Manfred

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4/17/2008 1:59 PM	Rate (0)
J_Bell Posts: 5822 Rating: (412)	Hello, I am sorry but I have to post some of my views on that too, because I think it is important. First of all, I am more onto the PLC side... so please excuse that I focus myself on the PLC and the Protocol. On the PLC all today’s CP’s and CPUs with PN Interface an up to date FW are able to handle TCP and UDP, seen form the Protocol point of view. Formerly only 2 CPs and the early PN CPUs couldn't but let us forget about these. Seen form the Protocol point of view we have to say that neither TCP/IP nor UDP/IP are cyclic Protocols. At least not as long as you program them that way. You usually senda Telegram to a IP Address and the partner with this IP Address receives it. This is the same for both, but now the difference starts. In case of the TCP Protocol the receiver sends a acknowledgement to the sender to show that the Data has been successfully received or has to be repeated. UDP does not have this. Just imagine that you are right in front of a large wood and you shout something into this wood. You may think that there is someone or someone special you want this message to be directed to... but you do not know if this has reached the person you want to reach. With TCP this can not happen, because TCP establishes, before you send the first Telegram, a Connection and verifies that way that the Communication partner required is there. Seen from the performance point of view you have to see that the maximum size of a UDP Datagram is up to 2048 Byte, TCP reaches 8092 and more... depending on the Interface used. The UDP Header is rather short, compared to the TCP Header, therefore the UDP Telegram can be created and processed much faster than the TCP... but we talk here about nanoseconds, so the PLC and Simotion are surely slower. I hope I made my point clear here. I am sorry but about this subject a complete Book could be written, but I tried to put my essential points in here. Best regards J_Bell
J_Bell Posts: 5822 Rating: (412)
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