User manual

Global Data (Publish/ Subscribe)
188
33002479 06 07/2008
Planning the Global Data (Publish/Subscribe) System
Overview Global Data service is a real-time publisher/subscriber mechanism that provides the
most efficient data exchange for PLC application coordination.
Devices that support Global Data are arranged in a distribution group for the
purpose of application variable exchange and synchronization. Each Global Data
device can publish up to one network (application) variable and subscribe to up to
64 network (application) variables.
The Quantum NOE’s embedded Global Data Configuration Web page provides a
configuration screen (see Quantum NOE Global Data Configuration, p. 193) to
determine which and how many application variables are exchanged with this
service. After configuration, exchanges between all stations belonging to the same
distribution group are done automatically.
The Global Data service uses %MW (4x registers) for Global Data exchanges.
Key Features of
Global Data
The main features for Global Data are:
z One publisher and many subscribers
z A device can publish one network variable of up to 512 %MW words (4x registers)
z A device can subscribe to up to 64 network variables of up to 2048 %MW words
(4x registers)
z A device subscribes to the complete network variable
z One distribution group per network IP address
z Application-defined publication rate
z Up to 64 Global Data Network variables (numbered from 1 to 64) can be part of
the data distribution group
z An NOE has only one multicast address. Consequently, it can only publish and
subscribe within the group
z A device can participate in several distribution groups by using multiple NOEs in
the rack
Global Data has an advantage over client/server services when more than one
subscriber is receiving the same data since only one transaction is necessary for all
subscribers to receive the data. There are two benefits:
z the reduction of overall network traffic
z tighter synchronization of multiple subscribers