Technical data

ETHERNET • 121
Network Communication
WAGO-I/O-SYSTEM 750
ETHERNET TCP/IP
5.3.2.1 ETHERNET
ETHERNET address (MAC-ID)
Each WAGO ETHERNET fieldbus coupler is provided from the factory with a
unique and internationally unambiguous physical ETHERNET address, also
referred to as MAC-ID (Media Access Control Identity). This can be used by
the network operating system for addressing on a hardware level.
The address has a fixed length of 6 Bytes (48 Bit) and contains the address
type, the manufacturer’s ID, and the serial number.
Examples for the MAC-ID of a WAGO ETHERNET fieldbus coupler
(hexadecimal): 00
H-
30
H-
DE
H-
00
H-
00
H-
01
H.
ETHERNET does not allow addressing of different networks.
If an ETHERNET network is to be connected to other networks, higher-
ranking protocols have to be used.
Note
If you wish to connect one or more data networks, routers have to be used.
ETHERNET Packet
The datagrams exchanged on the transmission medium are called
“ETHERNET packets” or just “packets”. Transmission is connectionless; i.e.
the sender does not receive any feedback from the receiver. The data used is
packed in an address information frame. The following figure shows the
structure of such a packet.
Preamble ETHERNET-Header ETHERNET_Data Check sum
8 Byte 14 Byte 46-1500 Byte 4 Byte
Fig. 5-9: ETHERNET-Packet
The preamble serves as a synchronization between the transmitting station and
the receiving station. The ETHERNET header contains the MAC addresses of
the transmitter and the receiver, and a type field.
The type field is used to identify the following protocol by way of
unambiguous coding (e.g., 0800
hex
= Internet Protocol).
5.3.3 Channel access method
In the ETHERNET Standard, the fieldbus node accesses the bus using
CSMA/CD (Carrier Sense Multiple Access/ Collision Detection).
• Carrier Sense: The transmitter senses the bus.
• Multiple Access: Several transmitters can access the bus.
• Collision Detection: A collision is detected.
Each station can send a message once it has established that the transmission
medium is free. If collisions of data packets occur due to several stations
transmitting simultaneously, CSMA/CD ensures that these are detected and the
data transmission is repeated.
However, this does not make data transmission reliable enough for industrial
requirements. To ensure that communication and data transmission via
ETHERNET is reliable, various communication protocols are required.