Transports

A driver speaks a protocol; a transport carries it. Which transports a driver supports is part of its metadata, and the connection string names the one you want between the protocol code and the ://:

modbus-tcp:tls://192.168.1.100:802
        ^^^ ^^^
    protocol transport

Leave it out and the driver’s default transport is used. Every option a transport accepts is prefixed with its code, so tcp.connect-timeout-ms and cotp.tpdu-size stay apart in one connection string. The tables on the pages below are generated from the transports themselves.

Network

TCP - plain TCP client socket
UDP - connectionless datagrams, including broadcast
TLS - TCP secured with certificates
TLS-PSK - TCP secured with a pre-shared key
COTP - ISO-on-TCP, as used by Siemens S7
Raw Socket - Ethernet frames below IP

Serial and fieldbus

Serial Port - RS-232, RS-485 and USB adapters
CAN bus - the shared API the CAN transports implement
SocketCAN - a real CAN bus through the Linux kernel
Virtual CAN - an in-memory CAN bus

Offline

PCAP Replay - replays a recorded capture instead of a device

A test transport is also registered. It is an in-memory stand-in used by PLC4X’s own unit tests, it is not usable from an application, and it is deliberately left out of the supported transport lists on the protocol pages. If you see it in driver metadata, filter it out.