basic difference - OPC-DA vs OPC-UA ?

can someone explain the basic difference

between OPC-DA vs OPC-UA ?


am i correct that UA is relatively new where as DA has been around for some time

EICS said:

can someone explain the basic difference

between OPC-DA vs OPC-UA ?


am i correct that UA is relatively new where as DA has been around for some time

Click to expand...

UA was developed nearly 10 years ago I believe. However uptake seems to have been a bit slow.

DA relies on Windows DCOM components, and is very, very finicky when it comes to communicating with clients that don't reside one the same machine. It also relies on DCOM security settings, which generally get turned off in an attempt to get the bloody thing to work.

UA was a complete rebuild, using no inherently windows-only components. In theory, Linux OPC UA servers and clients are possible (not sure if they exist). It uses IP addresses or host names to define end points and works quite ok over VPNs or routed networks.

If its a new system and both client and server support it, go for UA.

Matrikon make UA/ DA wrappers and tunneling software if you're stuck with one side needing to be DA.

Many thanks saffa
all good info there.

- OPC UA is platform independent ... in fact I wrote my own OPC UA Client for Android

- OPC UA does not need to be secured through VPN due it already has its own encryption and authenticacion using trusted certificates.

And much more:
- The messages can be up to 16 Mbytes in size and also the protocol has the ability to split the message into pieces if some send or receive buffer is smaller. This means that several thousand tags can be read in a single request.

- The documentation is extensive, well structured and available for free to all, but if you are interested then be prepared to read thousands pages.

In short a far superior protocol compared with others in use actually.

It is to be hoped that in the future PLC manufacturers will incorporate it natively into their products.
Siemens and a few other already did.

A drawback is in the added complexity and if you don't watch out the certificate becomes invalid on site after a year or so. Oh joy.

spaderkung said:

A drawback is in the added complexity and if you don't watch out the certificate becomes invalid on site after a year or so. Oh joy.

Click to expand...

It depends how you get your certificates created, but yeah. Certificate based authentication is an IT topic that gets introduced into a lot of OT applications without most of us really understanding the background.


OPC UA does allow guest/no security, as well as username/password for cases where medium security is OK.

It is more usual for certificates to be generated with an expiration of 5 or 10 years, my client generates them by default for 10 years.

As mk42 says, you do not always need to use certificates, if you select security=none and anonymous or username/password login, then certificate(s) are not needed.

An explanation of the cryptography used by OPC UA and many other encrypted protocols https://en.wikipedia.org/wiki/Public-key_cryptography

lfe said:

In short a far superior protocol compared with others in use actually.

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Perhaps that depends on the purpose of the protocol.

many thanks for all your replys.