Chapter 3. DHTP - The DataHub Transfer Protocol
The DataHub Transfer Protocol (DHTP) is used by the DataHub Tunnel/Mirror feature, as well as the Cogent DataHub™ service for Azure service, ETK, and connected clients to send and receive data in real time over TCP across a LAN, WAN, or the Internet. Originally built upon HTTP, DHTP also supports SSL and WebSocket protocols. In continuous development for over 20 years, DHTP is open and documented in two parts, as the DataHub APIs and the DataHub Command Set.
![[Note]](images/note_1156523861.png) | |
Each DataHub instance connected by DHTP requires its own license. License verification is done between DataHub instances over the network. Occasionally a slow network may result in misleading "no license" errors. Please refer to TCPLicenseTimeoutSecs for more information. |
Additionally, the DataHub program supports various protocols that are native to commonly used industrial applications, like ODBC, OPC, Modbus, etc. The ETK supports OPC UA and Modbus.
Examples
As shown in the above diagram, DHTP may be used for the following connection types:
DataHub instance to DataHub instance for DMZs and tunnelling on LANs and WANs
ETK to DataHub instance for on-premise connections and edge procsssing
Custom programs to a DataHub instance, to integrate virtually any application
Applied DHTP Features
The DataHub program uses DHTP to provide these important Industrial IoT features:
Low Bandwidth & Low Latency: Consumes minimal bandwidth, while functioning with the lowest possible latency
Ability to Scale: Can support hundreds or thousands of interconnected data sources and users
Real-Time: Adds virtually no latency to the data transmission
Intelligent Overload Handling: A broker (DataHub instance or ETK) responds appropriately when a data user is unable to keep up with the incoming data rate
Quality of Service: Guarantees consistency of data, preserved through multiple hops
DHTP Protocol Features
DHTP communications between and among DataHub instances, ETK, and their clients meet the following criteria for secure, robust industrial and IIoT data communications:
Closed Firewalls: Keeps all firewall ports closed for both data sources and data users
Interoperable Data Format: Encodes the data so that clients and servers do not need to know each others' protocols
Can Daisy Chain Servers: Multiple instances of brokers (DataHub instances or ETK) can be connected to support a wide range of collection and distribution architectures
Propagation of Failure Notifications: Each client application can know with certainty if and when a connection anywhere along the data path has been lost, and when it recovers
Simple: Message syntax is simple enough to be implemented even on resource-constrained devices
Streamable: Messages can be concatenated and streamed without requiring intervening acknowledgements. This allows clients and servers to communicate asynchronously, reducing latency and significantly improving throughput