122 • Fieldbus CommunicationETHERNETWAGO-I/O-SYSTEM 750PROFINET IOHowever, this does not make data transmission reliable enough for industrialrequirements. To ensure that communication and data transmission viaETHERNET is reliable, various communication protocols are required.4.1.3.3.1 IP-ProtocolThe Internet protocol divides datagrams into segments and is responsible fortheir transmission from one network subscriber to another. The stationsinvolved may be connected to the same network or to different physicalnetworks which are linked together by routers.Routers are able to select various paths (network transmission paths) throughconnected networks, and bypass congestion and individual network failures.However, as individual paths may be selected which are shorter than otherpaths, datagrams may overtake each other, causing the sequence of the datapackets to be incorrect.Therefore, it is necessary to use a higher-level protocol, for example, TCP toguarantee correct transmission.IP addressesTo allow communication over the network each fieldbus node requires a 32 bitInternet address (IP address).AttentionInternet addresses have to be unique throughout the entire interconnectednetworks.As shown below there are various address classes with net identification (netID) and subscriber identification (subscriber ID) of varying lengths. The netID defines the network in which the subscriber is located. The subscriber IDidentifies a particular subscriber within this network.Networks are divided into various network classes for addressing purposes:• Class A: (Net-ID: Byte1, Host-ID: Byte2 - Byte4)e.g.: 101 . 16 . 232 . 2201100101 00010000 11101000 000101100 Net-ID Host-IDThe highest bit in Class A networks is always ‘0’.Meaning the highest byte can be in a range of’0 0000000’ to ‘0 1111111’.Therefore, the address range of a Class A network in the first byte is alwaysbetween 0 and 127.
