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====== Overview ======

The DHD Communication Server (DHDCS), has two main tasks:

  - The DHDCS distributes the UDP network traffic to all DHD applications at the same time on the same Windows PC. Because of a Windows restriction that allows only one application to access the UDP network traffic, the DHDCS is always running in the background as soon as you start a DHD application on the PC. 
  - The DHDCS allows to monitor Series 52 and RM4200D systems in the same network and to record their activities. This is especially useful for monitoring certain functions in complex systems or for troubleshooting. To do so, you can use the user interface of the DHDCS to set up the monitoring.

Series 52 systems have an Ethernet port to communicate with each other or with one or more PCs running DHD applications. For this communication, the network protocols UDP and TCP/IP are used as follows.

==== UDP protocol ====
 The  Core uses the connectionless UDP protocol for communication with other DSP cores and between DSP cores and PCs with DHD applications. During this communication, a DSP core sends UDP packets as broadcast that are read by all recipients and evaluated if necessary. The data in the packet do not require any feedback, thus being an information to all. It is up to the recipient if he evaluates the data. The following information is broadcasted via UDP:

  - A heartbeat packet is sent each second from the DSP core. It contains information for all recipients, including device name, project ID, IP address and its Ethernet MAC address. This procedure is used for example by the Toolbox5 software to automatically show a list of all DSP cores available in the network.
  - Global Logic signals, Global Resources and Global Potentiometers are also transferred via UDP broadcast. Each device in the network analyses the Project ID of the sender. If this matches with the own Project ID, the payload data is evaluated further. If not, the UDP packet is discarded.
  - Certain operating conditions are also reported via UDP broadcast. This includes for example over-modulated audio inputs, communication problems of the DSP core among each others, errors on the CAN bus (only RM4200D), changes of the synchronisation sources. Special DHD applications like DHDCS analyse these messages and can generate a log file. 

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**Important**\\  To make the data transfer via UDP work correctly, all devices in the network have to be able to exchange UDP broadcast packets. If this is not possible, for example routers block the UDP traffic, devices **can not communicate** this way! In this case, ask your system administrator for assistance.
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==== TCP/IP protocol ====
 This protocol is mainly used by DHD applications that communicate directly with a DSP core. For this, a point to point connection is set up through the network that works in both ways. Using this data channel, the DSP core can report its status to the DHD application; the software can control the DSP frame. TCP connections are used for the following:

  - The TB8 software uses a TCP connection to exchange configuration data with the DSP core. The firmware of the DSP core is also updated this way.
  - The DHD applications DSP control and Remote Control use a TCP connection to monitor or remote control a DSP core.
  - The DHD application Snapshot Manager uses a TCP connection to read a snapshot from the DSP core or to save snapshots in the DSP core.

The DHD Communication Server is a self-contained software component that is integrated in all DHD applications accessing the UDP data stream. When you start a DHD application, the DHDCS starts automatically and runs in the background. If you start additional DHD applications, they also use the DHDCS which is running already. The data transfer of all active DHD applications is processed completely by the DHDCS. The DHDCS is only quitted when the last DHD application that is accessing it is closed as well.

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**Tip**\\  As a user of a DHD application, you do not have to worry about starting or quitting the DHDCS. Both will be done automatically in the background. If for some reason this does not work, the affected DHD application shows a warning message.
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As you can see in the figure, when the DHDCS is running, the notification area in the Taskbar shows a small DHD logo like this . A double click on this icon opens the main window of the DHDCS.

[{{ :dhdcs:tray_icon.png?nolink |//Icon of the active DHD Communication Server in the notification area of the Windows Taskbar.//}}]