ETport / E4 / MCM TCP Socket Connection Limits and Modbus TCP Client Capacity
The ETport / E4 / MCM platform has a hard maximum of 16 open socket connections total. This includes both internal services running on the device and external client connections.
Standard Socket Usage
Under normal operation, several sockets are already allocated to built-in services, including:
• HTTP (web interface)
• Modbus TCP
• BACnet
• ETport API (finder / utility access)
• NTP time synchronization
This typically leaves approximately 10 general-purpose sockets available for external client connections.
Increasing Available Connections
If certain services are not required, additional sockets can be made available:
• Disable BACnet: frees 1 socket
• Disable web posting: may free 1 socket during posting intervals
• Disable NTP: may free 1 additional socket
With BACnet and web posting disabled, approximately 12 sockets are typically available. Disabling NTP may increase this to 13 sockets.
Important: Reboot the device after disabling services so the socket resources are fully released.
Web Browser Usage
The web interface was designed primarily as a configuration and diagnostic tool, not as a continuously used operational interface.
Many modern browsers open multiple simultaneous connections automatically. This behavior varies by browser and cannot be fully controlled. As a result, one browser session may consume more than one socket.
For best performance, limit the web interface to one active browser session.
Modbus TCP Client Behavior
Different Modbus TCP clients manage connections differently:
• Some clients keep a connection open continuously
• Some clients open a new connection only when polling
• Some clients reconnect automatically if disconnected
If all sockets are in use, the device will automatically close the least recently used connection to free capacity. Most properly designed Modbus TCP software should reconnect automatically when needed.
Recommended Practical Limits
Although the absolute maximum depends on active services and client behavior, we generally recommend:
• Up to 8 Modbus TCP connections for comfortable operation
• Up to 10 total active connections may be workable depending on polling rates and browser usage
Performance at higher connection counts depends heavily on:
• Polling frequency
• Number of registers requested
• Simultaneous browser sessions
• Other enabled network services
Example Scenario
A system with:
• 5 polling devices
• 2 technician web sessions
would likely be workable if polling rates are moderate and browser usage is limited.
Summary
The ETport / E4 is a specialized embedded communications platform designed for reliable metering applications. While it can support multiple simultaneous clients, best performance is achieved by limiting unnecessary services, minimizing browser sessions, and keeping Modbus polling rates reasonable.