Manual EKS Ethernet TCP/IP
2547185-01-10/22
Subject to technical modifications
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8 Data transfer via the Ethernet TCP/IP interface
8.1 Communication
This chapter primarily describes communication between a PC and the read/write station (referred to as the
device
in the following).
The commands
Program (write) Electronic-Key
Read Electronic-Key
are issued using the TCP/IP protocol.
Integration of the read/write station with Ethernet interface into the user’s PC application is supported by an
optionally available ActiveX
module (order no. 100665) (usable if user programs under MS Windows
support
ActiveX
). The EKS can thus be used in conjunction with process visualization, for example.
The ActiveX
module is used as a protocol driver for the TCP/IP data transfer protocols described in the following
.
Upon request, Euchner will make available a shared library as an interface to a Linux operating system.
Information!
The shared library only supports the EKS during reading.
To ensure communication stability, a maximum of one connection to the application is allowed. In parallel, an
additional connection can be established via the web interface.
8.2 Basic message structure
8.2.1 IP – Internet Protocol
The internet protocol defines the basis for data transfer. It guarantees data transfer by connectionless,
unsecured transport of data packets. IP provides an addressing mechanism for unambiguously identifying the
transmitter and receiver. This is done by means of IP addresses.
In addition to the actual user data that are to be transferred, a data packet also contains other important
information to facilitate problem-free data transfer. This additional information is also referred to as the packet
overhead or header.
8.2.2 TCP – Transport Control Protocol
TCP takes care of the handling and security of the IP data packets. It establishes a connection between two
network stations for the duration of data transfer. The conditions for data transfer (e.g. the size of the data
packets) are defined when the connection is set up. TCP operates according to the so-called client-server
principle. The network station that sets up a connection represents the client. The addressed network station is
known as the server.
TCP provides every data packet with a checksum and therefore ensures that any data loss is detected. A
sequence number is also transferred that calculates a so-called acknowledge number according to a fixed
algorithm. This acknowledge number is sent back to the transmitter. In this way, the receiver acknowledges that
the data packet has been received correctly. If this is not the case, the receiver requests the data packet again.
A further task of TCP is forwarding of data packets to the correct application. These applications (so-called
services) are addressed by means of different port numbers (e.g. port 80 for HTTP).