The Ethernet port on the RM420-850 Communications Controller complies to the standard 100Base-TX, IEEE 802.3u. This means, the network connected to it must run at least with a speed of 100 Mbit/s. Do not try to connect the RM4200D to a network running on 10 Mbit/s! Even if it looks like this will work, it does in fact not!

Depending on the firmware version of the RM4200D, the Ethernet interface of the RM420-850 Communication Controller operates with different speeds:

If you connect other network equipment to the RM4200D, it must be able to handle these specifications. Most current networking hardware does this automatically. However, if you experience connection problems, make sure the requirements are met. This is particularly important if you connect a PC directly to the RM4200D using a crossover Ethernet cable. If you do this, make sure you have set the properties of the network adapter in Windows to the right values. Most network adapters have an "Auto-Detect" option - use this one!

	Important
	You can operate several RM4200Ds and Windows-PC running DHD applications within the same network segment. However, you should always use Ethernet switches to connect them to each other. Do not use older Ethernet hubs! Switches provide much better data throughput, because they eliminate collisions between network packets.

If possible, use Ethernet switches that automatically adjust their port speed to the speed of the node connected to a particular port. Also, if you are using VLANS or routers, make sure all devices on a shared network can exchange data on the ports and protocols described in the next section.

Protocols Used

RM4200D systems use both the protocols TCP/IP and UDP for communication. A direct TCP/IP connection is used for direct data transfer from an RM4200D to a PC or vice versa, e.g. for downloading a configuration or updating the firmware. All optional DHD applications (Access, Route, RC420, Setup Manager) also use direct TCP/IP connections to the RM4200D.

In contrast, UDP is used to transmit control data for the following functions:

• Global Logics.

• Global Potentiometers.

• Global Ressources.

• System messages for display and logging in the Maintenance Window and the DHD Communication Server.

Since the UDP protocol is connectionless, the sending node transmits data onto the network without getting any acknowledge from receiving nodes. Furthermore, the operation system running in the RM4200D does not send UDP packets to certain destination addresses. Instead, it uses Broadcast addresses to send its data to all network nodes within the same subnet. All receiving nodes analyze the contents of the received UDP packets and react accordingly, if necessary.

	Important
	For the communication to work properly, the network ports 2008, 2009 and 2010 need to be enabled both for TCP and UDP. Make sure you set up routers, firewalls and security applications on PC accordingly. Also make sure that UDP packets carrying a broadcast address are transmitted correctly.