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RS400 65 ROS™ v3.5
2.2.4 Transport Protocols
For supported protocols, with exception of Modbus, either UDP datagram or TCP connection
packets can be used to transport protocol data over the IP network. The Modbus data can be
transported only using TCP connection, following TCPModbus protocol. UDP supports all the
addressing modes of IP – unicast, multicast and broadcast. Therefore, if address learning is
enabled, UDP broadcasts will be sent across the network.
2.2.4.1 Transport for Raw Socket
TCP transport for RawSocket require configuration of connection request direction and remote
IP address and IP port for listening or requesting outgoing TCP connections. Only one outgoing
connection can be requested, but up to 64 connections can be accepted if port is configured to
listen to incoming connection requests. For ports configured to request connections and to listen
to incoming connection requests only one connection can become active.
RuggedServer™ will attempt to connect periodically if the first attempt fails and after a
connection is broken.
RuggedServer™ can be used to connect to any device supporting TCP (e.g. a host computer’s
TCP stack or a serial application on a host using port redirection software).
If UDP transport is configured for the port with Raw Socket protocol assigned to it, only one
remote host can communicate with devices on that serial port. The Raw Socket transparently
passes data and it cannot distinguish where to send packets received from connected devices,
as there is no concept of protocol. Any protocol can be encapsulated in Raw Socket.
2.2.4.2 Transport for Protocols with Defined Links
All protocols with defined links (source and destination addresses are part of protocol) can use
either TCP or UDP to transport data.
Device Address Table contains addresses and locations of devices configured (or learned) for
specific protocols.
If protocol is configured to use TCP connection to transport data, server will start listening to the
IP Port configured for protocol and. At the same time, TCP connections will be placed to all IP
addresses where devices for that protocol are attached. RuggedServer™ will keep only one
connection open to one IP Address on one IP Port.
2.2.4.3 Use of Differentiated Services Code Point (DSCP)
RuggedServer™ has the ability to set the DS byte in the IP header of outbound IP packets. The
value can be configured on an ingress serial port, and/or for a protocol. Which value will be
used depends on the protocol configured on a port and the transport configured for the
particular protocol.
UDP/IP transport supports DSCP setting per serial port or per protocol. If configuration contains
DSCP setting per serial port as well as per protocol then the system will use which ever setting
has a higher DSCP value.
TCP/IP transport supports per protocol DSCP setting. RawSocket and Modbus Server protocol
properties are configured per port as well, so they always support DSCP setting per serial port.