Rockwell-automation Ethernet Design Considerations Reference Manual Manual de usuario descargar pdf (Pagina 35)

Rockwell Automation Publication ENET-RM002C-EN-P - May 2013 35

Ethernet Infrastructure Features Chapter 3

Multicast Address Limit

In multicast communication, EtherNet/IP interfaces support a maximum of

32 devices that transmit multicast.

The multicast address limit is independent of the connection limit for a device.

Not all connections require a multicast address. In the case of produced and

consumed tags, one produced tag requires one multicast address, but it also

requires one connection for each consumer. If there are multiple consumers, the

one multicast address must use multiple connections.

Transmission Protocols

The network layer (Layer 3) provides switching and routing that create logical

paths, known as virtual circuits, for transmitting data from node to node.

Routing and forwarding are functions of this layer, as well as addressing and

internetworking.

Address Resolution Protocol (ARP)

An ARP request is a broadcast message that asks ‘who has this IP address?’. The

device that has that IP address responds and the requestor adds the IP address

and hardware address pair to its ARP cache. The original device can now send the

message. This protocol enables the network to learn and adapt to changes.

EXAMPLE

An Ethernet adapter that produces data uses a unique multicast address for

each I/O connection.

EXAMPLE

A Logix controller that produces tags uses a unique multicast address for each

produced tag.

1756 Controller

Device needs to send a

message to 130.151.3.4

Who has the IP address 130.151.3.4 ?

130.151.3.4

PowerFlex

I have IP

address

130.151.3.4

1734 POINT I/O

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Rockwell-automation Ethernet Design Considerations Reference Manual Manual de usuario Pagina 35