NOTE: The term "Multicast" in this FAQ does not refer to true IP Multicast.  Digi's UDP "Serial Multicast" uses a table of multiple target unicast IP addresses to forward serial data from one device server to multiple UDP destinations.  Even though Multicast IP addresses (e.g. 224.0.0.1) can be entered in the table, they are not supported and will likely not produce the desired results.

What is UDP Multicast and why would I need it?

UDP Multicast can be used to send serial data from one host to many devices at the same time.  Here are a few examples of how it maybe
implemented:

q       Transmit the time or a message to several displays devices simultaneously. 

q    Console monitoring.

q       Stock and Newswire tickers.

q       Send control information to many PLCs simultaneously.

Setting Up the Digi Device Servers:

This document outlines how to set up a simple UDP serial Multicast Source (Sending Device) to two UDP Destination Devices using any of the Digi device servers that support UDP Multicast.  Up to 64 destinations are supported.

NOTE: UDP is a connectionless protocol.  This means data is sent without the protocol ensuring its reliable delivery.  If reliable transmission is required, consider using TCP based communication, such as TCP sockets, RealPort or an IA protocol.

UDP does have some advantages over TCP.  The main advantage is that it requires less network overhead.  This is mainly due to UDP not requiring an acknowledgement from the receiving device, thus lost packets will not be retransmitted.  For example, if a sign does not properly receive the time, is it necessary to have the time retransmitted, if time will be updated again in a second or a minute?   

        F     Refer to the Digi Install and Configuration Guides and to http://supportold.digi.com for more information on setting up the Digi One
              device servers.

Notice the devices are connected via serial ports to Digi One device servers.  Devices 1 and 2 can be any UDP serial destination.  Up to 64 can be defined.  The PC could be any device that needs to send serial data to all destination devices.

Serial data is encapsulated from the sender (or source) into Ethernet / UDP.  The Digi One device server (shown as 172.16.5.51 above) then multicasts the data to the other Digi One device servers designated as recipients (or destination devices).  The received data is then converted back to serial data and sent out each device server’s serial port to the attached devices.

Assign IP Addresses:

IP addresses must be assigned to each Digi One device server.  From the factory, the units come with DHCP enabled.  Depending on the product, there are several ways to assign an IP address.  Here are three common ways to assign the IP address:

q       DHCP – default setting.  If no DHCP server is available the address will be 0.0.0.0. 
NOTE: DHCP can be disabled.

q       Digi Discovery Protocol (ADDP) – ADDP comes as part of the Digi setup program (either Digi Port Authority Remote or Digi Device and Terminal Server Setup) included on the Access Resource CD.  This can be used to find both configured (with IP address) and un-configured (no IP address) Digi One device servers on the local LAN.

q       ARP-PING – Add an entry to the ARP table on a PC using the MAC address of the unit; then ping the unit.  As an example from a Windows PC:

arp -s 192.168.2.2 00-40-9D-00-00-00

ping 192.168.2.2]

 F     Refer to the Digi One Device Server documentation and to http://supportold.digi.com for more information on assigning an IP addresses.

1.  If this is the initial configuration of the Digi One Single Port (Digi One IA), launch the Setup Wizard (dgcfgwiz.exe).  The Setup Wizard can be
     located in the driver files for the Digi One SP/IA.
2.  If you have already configured your Digi One Single Port (Digi One IA), you can follow the Web Interface configuration below.
     NOTE: You will need to be on the latest firmware version to follow this setup example.

The Outgoing Device is basically the sending device.  Any serial data entering the serial port will be forwarded to the target (Incoming) device servers via Ethernet.  The target servers are defined later in this setup procedure.  

Setup Wizard Configuration Option for UDP Client (Outgoing Device):

Use this procedure if this is the initial configuration of your Digi One Single Port (Digi One IA) Device Server.

1.   Launch the Setup Wizard (dgcfgwiz.exe).  The Setup Wizard can be located in the driver files for the Digi One SP/IA Device.
     

1. Open a browser window (i.e. Internet Explorer or Netscape) and point to the IP address of the UDP Client (Outgoing Device).  Using the IP address from our example above: http://172.16.5.51.
2. You will be prompted to enter a user name and password:

User Name: root

Password: dbps

3. You should see a screen similar to the following after logging in:
    

4. Under Configuration select Serial Port.  
5. Select the proper flow control and port settings to match that of the device connected to Digi One SP/IA Device's serial port. 
   
6. Select UDP Client/Server Settings.
   NOTE: If you get a message indicating UDP is unavailable, you may have a configuration that is preventing you from using UDP 
   (i.e. TCP Autoconnect).  This will need to be disabled before UDP will become available.
   
7. Under UDP Client:, specify the following:
       A. Description: Give a name to your setup.
       B. Destination: Enter the IP Address of the device you are sending data to.
       C. UDP Port: Is the UDP port to use, which is determined by the destination system. :
            NOTE: Here are some tips on specifying port numbers: 
            -Use the port required by the application on the destination system you are running.
            - For a raw connection to the serial port on another Digi device, use 2101, unless the default configuration has been changed.
        D. Click Add.
        E.  Repeat if you have multiple destinations you will be sending data to.
             NOTE: Up to 64 destinations can be configured here.  

8. Three conditions can be used to tell the UDP Client (Outgoing Device) device server when to send its buffer contents to the UDP Server (Incoming Device).  Whichever condition is met first will trigger the server to send the contents of the buffer to the destination devices:
1. Send data when the following string is found: The string selected will tell the Digi One SP/IA Device that the message is complete and to forward the contents of the buffer to the destination devices.  The options are: CR (Carriage Return), CR/LF, or Custom.  Custom (which allows up to any 4 characters).  
   NOTE: There is an option to strip the string before sending the contents to the UDP Server (Incoming Device).
   If there is no string received and buffer is full, all the contents will be forwarded to the UDP Server (Incoming Device).
2. Send data after the following number of milliseconds: How long the server will wait before forwarding the buffer contents.  By default, after100 ms, if no data is received from the serial device, the contents of the buffer will be forwarded to the UDP Server (Incoming Device).  The idle timer is adjustable from 1 – 60000 ms.  If there is no idle time, all contents will be forwarded when the buffer is full.
3. Always send data after the following number of bytes: How many characters the buffer will accumulate before forwarding its contents.  By default, after 1024 bytes of data, the contents of the buffer will be forwarded to the UDP Server (Incoming Device). This number is adjustable from 1 byte to 4096 bytes.

9. Click Apply to save settings.
   

Configuring the Digi One SP/IA as a UDP Server (Incoming Device):  

1.  If this is the initial configuration of the Digi One Single Port (Digi One IA), launch the Setup Wizard (dgcfgwiz.exe).  The Setup Wizard can be
     located in the driver files for the Digi One SP/IA.
2.  If you have already configured your Digi One Single Port (Digi One IA), you can follow the Web Interface configuration below.
     NOTE: You will need to be on the latest firmware version to follow this setup example.

The Incoming Device is basically the receiving device.  

Setup Wizard Configuration Option for UDP Server (Incoming Device):

Use this procedure if this is the initial configuration of your Digi One Single Port (Digi One IA) Device Server.

1.   Launch the Setup Wizard (dgcfgwiz.exe).  The Setup Wizard can be located in the driver files for the Digi One SP/IA Device.
     

Web Interface Configuration Option for UDP Server (Incoming Device):

Other than assigning the Basic Serial Settings, the only UDP Server setting is knowing the UDP port number.  This is the UDP port
number that the UDP Server (Incoming Device) receives on.

In the sample UDP Multicast setup at the beginning of this document, the end devices could be PLCs, signs, printers or most any other serial device.  However, initially testing these devices can be difficult if they are in a remote location, such as a plant floor.

A simple test bed is to use a Windows PC running terminal emulation software such as HyperTerminal.  You can use one or multiple PCs to act as the source and destinations.  For example, a two PC setup like the following would work as follows:

On the UDP Server PC (Incoming Device - Destination), open up two HyperTerminal sessions – one on COM1 and the other on COM2.  Make sure the port settings for baud rate, parity, etc. match that of the Digi One SP/IA Device's serial port.  Also make sure no other programs are accessing these ports.

On the UDP Client PC (Outgoing Device - Source), open a HyperTerminal session on COM1.  Start typing in the HyperTerminal screen.  This same text should appear on the two HyperTerminal sessions of the UDP Server PC (Incoming Device - Destination).  The timing of when the text appears depends on the buffer trigger settings on the UDP Client PC (Outgoing Device - Source).

Another simple test is to send a large text file from the Source to the Destinations.  From a command (DOS) prompt enter the following:  type large_text_file.txt > COM1:

You can also vary the port buffer settings to see how the changes affect the output sent to the terminal window on the Destination PC.