Today, computer networks are used for a great variety of applications. Office printer sharing, access to file servers, streaming of audio and video and also control data for embedded systems (as the RM4200D) runs on the same network infrastructure. Because these networks are so diverse in their use of protocols, they are often called heterogeneous networks.
Nodes on such a network are often PCs running Windows, but there can also be printers, networked disk drives or servers running Unix, Linux or any other operation system. All these devices use many different protocols on top of TCP/IP and UDP. For instance, the announcement of services like file sharing or printer services uses UDP broadcasts. For most devices, this works perfectly. However, if an RM4200D is connected to such a mixed network and if the level of UDP traffic becomes too high, this may cause problems for the RM4200D.
Here is why:�
Since the RM4200D uses UDP broadcasts for transmitting its control information, each DSP frame on the network must inspect all incoming UDP packets with a broadcast address. This also includes packets from other nodes on the network, for instance Windows PCs announcing their file sharing services. An RM4200D DSP frame will only react to packets from other DSP frames or DHD software running on Windows PCs. However, it has to inspect any incoming UDP packet, even if it is not sent by a RM4200D system. This inspection uses computing power of the RM420-850 Communications Controller.
Under certain circumstances, a high level of incoming UDP traffic thus can cause data buffers to overflow within the controller. This happens even if the data in the UDP packets is not used, because it was not destined for the RM4200D! In turn, this can cause the controller to delay its main task, which is running the DSP frame. In extreme cases, it may also cause the controller to shut down the Ethernet port completely.�
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Therefore, you should avoid running a RM4200D system within a network with too much UDP traffic, since this can cause instability of the Communications Controller. |
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To make sure all communication between RM4200D systems and PCs running DHD applications runs smoothly, design your network according to the following rules:
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Put all RM4200D systems on their own, isolated network. Put all PCs running DHD applications on the same network. Make sure, no “non-DHD traffic” gets on this network.
Important Do not run RM4200D systems within an existing office network!
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Always use Ethernet-Switches. Do not use older Ethernet hubs or “Switching Hubs”.
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Avoid using connections with a speed of 10 Mbit/s. Always use connections with 100 Mbit/s.
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If you are using a PC, make sure you set its network adapter to “Auto-detect”.
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UDP broadcasts will only work within the same IP subnet. If different RM4200D systems need to communicate with each other they must have IP addresses within the same subnet.
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If different RM4200D systems are located within different IP subnets, they can not exchange data using the UDP protocol. However, you can still access them from a PC running a DHD application by using their IP address.
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If you use routers, firewalls etc. make sure network traffic on ports 2008, 2009 and 2010 is carried both on TCP and UDP.
If you need to access the RM4200D systems in their separate network, you need to run DHD application software on one or more PCs connected to this network. Depending on your organisations policies and its IT infrastructure this is sometimes not straightforward.
Therefore, here are some strategies that might work for you:�
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Use a dedicated PC to access the RM4200D systems. Put this PC on the separate network only. If you need to transfer data to and from this PC, use a CD-R or an USB memory stick.
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Put two network cards in the PC. Connect one to the separate network, the other one to the office network. However,do not turn routing between the two networks on!. Also protect your PC against viruses coming from the office network. While viruses cannot infect DHD systems directly, they can cause heavy network traffic in all networks connected to the infected PC!
Important Make sure the PC does not route network traffic between its two network interfaces. On Windows, this feature is called “Internet Sharing”. Turn it off using the Network Control Panel in System Preferences.
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Use a dedicated PC within the separate network. Either put two network cards into this PC or use a router, firewall or VPN solution to connect from the outside to the separate network. Remote control the service PC inside the network with remote control software (PC Anywhere, VNC, Timbuktu etc.)
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Install a VPN gateway between the separate network and your office network. Set up the VPN in a way that only authorized users and/or authorized PC can connect to the VPN. Either use the VPN clients to control RM4200D systems directly or use them to remote control a service PC inside the RM4200D network.
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Have no special PC inside the separate network. Use a special service laptop or PC and plug it into the RM4200D network when necessary. Make sure, only authorized users have physical access to the network socket for this PC.
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Make sure you also read Chapter 3.3 – Connecting the Software to the Devices in Part 3 of the RM4200D Documentation (Configuration Manual). |
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You (or your network administrator) should have the necessary knowledge about all network issues described. If you have any questions, always ask your administrator or read any book on computer networking.�
You can also use your favourite Internet search engine or the following links to get more information:�
| Ethernet: | http://en.wikipedia.org/wiki/Ethernet |
| Internet Protocol - IP: | http://en.wikipedia.org/wiki/Internet_Protocol |
| Subnetz: | http://en.wikipedia.org/wiki/Subnetwork |
| Transmission Control Protocol - TCP: | http://en.wikipedia.org/wiki/Transmission_Control_Protocol |
| User Datagramm Protocol - UDP: | http://en.wikipedia.org/wiki/User_Datagram_Protocol |
| Broadcast: | http://en.wikipedia.org/wiki/Broadcast |