Alive mechanism of manager connections

The alive mechanism in WinCC OA serves for connection controlling between the single managers. Each manager sends alive messages  at definable intervals. The managers receive the alive messages via the UDP port. The mechanism  is used to detect  connection breakdowns between single managers and can be configured easily via two entries in the config file.

UDP (User Datagram Protocol) is a connectionless transport protocol that is based on IP. UDP does not provide check of the message delivery but it is faster than TCP. UDP is defined via the standard 6 and RFC (RFC = Request For Comments). RFCs are standard documents which concern the Internet and TCP/IP.

Each manager in WinCC OA can receive and send alive messages (if the manager has an open server port). Additionally, each manager sends alive messages  over  the normal manager connection (secured TCP connection) in order to detect a connection  breakdown. This means that the respective manager knows  over the TCP connection if the messages arrived. The managers send alive messages at ten seconds interval by default if the manager, which has an open server port, does not run on the same host. In case of a remote UI this could look like following:

Figure: Alive messages between managers

In this configuration the event manager  knows  that at least one alive message is delivered every 10 seconds

from the UI over the UDP port.  Additionally, the UI sends over the TCP connection an alive message

during the same time period in order to detect a possible breakdown.

There are two config entries in the config file for configuring the alive mechanism:

1. alivePort: Can be defined everywhere except in the [general] section and defines on which  UDP port a manager receives alive messages . If there is no entry and the manager is a server (Data, Event, Dist, Redu) the TCP server port is also the UDP server port (data: 4897, event: 4998).
    

2. aliveTimeout: can be defined everywhere except in the [general] section. The entry defines at which intervals (in seconds) the alive telegrams of this manager must be received, when the target manager provides an alive port. The manager itself sends about 10 alive telegrams over this period. If the target manager does not receive any telegrams over this period, the target manager closes the connection. The value 0 deactivates the sending of alive telegrams and the monitoring of the target manager. Negative values are only valid for connections between managers that run on different computers. Positive values are valid for all manager connections. The target of alive managers can be any manager to which the alive manager builds a connection and which provides an alive port. Normally this is the Event and possibly the Data manager. For Dist manager also the Dist manager of the coupled systems. The receiving of the respective manager can be deactivated by using the config entry "alivePort = 0".

Debug levels

The receiving of alive messages can be monitored via the debug outputs of the respective managers in the Log Viewer.