function blocks encapsulate UDP multicast services as prescribed in
subclause 5.5 of the Compliance
Profile. The datagram payload is limited to 1472 octets of
encoded data so that each PUBLISH/SUBSCRIBE transaction can be
accomplished in a single Ethernet packet under IPv4.
indicate when this limit is exceed by encoding in a
block or decoding in a
block is instantiated in an environment that does not support UDP
communication, the block automatically switches into the local multicast design
pattern, with a channel whose name corresponds to the
input of the block, and whose content consists of an instance of the
class containing the ASN.1 encoded data.
The FB interfaces shown above and the service sequences below
illustrate the operation of this service for
n = 3.