Hi all,

I am using a CPU S7-315 2 PN/DP (315-2EH14-0AB0) and I am sending data via Open TCP to an IT application.

My problem is that I am limited to 1460 bytes for each message and I need more.

I checked the help (Topic: Relationship between CPU and Protocol Variant Used) for the connection parameters and that is the length limit if I have a connection type equal to B#16#01.

According to the help file, i should be habble to change it to B#16#11 wich I could send 32767 bytes for the current cpu. The problem is that if I change the connection type to 16#11 I cannot connect to the IT system.

I tried these with fw 3.2.11 and 3.1.1. Both with the same behaviour.

Any ideas?

Thanks in advanced,

Daniel

Hello Daniel,

probably little mistake, connection type can be 16#0B - hex 11.

Duris_I

Hello Daniel,

probably little mistake, connection type can be 16#0B - hex 11.

Just tried it and it doesn't work either.

It would be funny though if help file made a mistake like that hehe

Navnag

Hello

How are you assigning the parameters?

If you are not already using, I would suggest that you should use the  Open Communication wizard from the below link. It will help avoid any parameterisation errors :

Wizard for creating connection data for open TCP/IP communication (Open Communication Wizard).

Additional useful information is available in the following threads :

How do you program the communication blocks FB63 "TSEND", FB64 "TRCV", FB65 "TCON" and FB66 "TDISCON" in order to use the TCP protocol for data exchange by means of the integrated PROFINET interface of an S7-300/S7-400 CPU? 

In the case of open TCP/IP communication via Industrial Ethernet using T blocks with IE CPs and CPUs, why are different amounts of messages sent when the maximum length of 1452 bytes of user data is transferred? 

Hope this helps

Cheers
Navnag

I also used Open communication wizzard. It configures the connection type to 16#11 also and I have the same result.

Thanks to your last link, I decided to check the protocol limits. It seems that communication between two PLC's can expand the original protocol limits, but due to the fact that I am communicating to an IT application I am a little bit more limited...

I found the following information that might explain my problem 

http://stackoverflow.com/questions/2613734/maximum-packet-size-for-a-tcp-connection 

The absolute limitation on TCP packet size is 64K (65535 bytes), but in practicality this is far larger than the size of any packet you will see, because the lower layers (e.g. ethernet) have lower packet sizes.

The MTU (Maximum Transmission Unit) for Ethernet, for instance, is 1500 bytes.....

Thanks for the help 

RIP

1test

On the German forum there was asked the question what open TCP/IP means. The links here only suggest that it is related to plc communication. Is there any information what the "open tcp/IP" thing means in gernerall?

 Regarding Siemens PLC's you have 2 types of TCP communication. The Open TCP/IP that I think is the normal TCP protocol used by IT applications and the ISO on TCP that is the last one with some enhancements. Open TCP is based on ip addresses and the ISO TCP uses devices names (TSAP) to establish conection between two devices.

This is the main diference that I noticed when using one or another. I bet that there is a lot more technichal diferences between both but I am not an networks expert