The function of a communication channel is to provide a mechanism for transferring data externally using different electrical standards to form a communication Port. The actual electrical interface is achieved by means of hardware, but the channel registers provide the user with facilities for selecting transfer timings and format, and for reading and writing data.

A UDP/IP Ethernet Communication channel can be used for transferring P-NET packets over an Ethernet network. The P-NET packets are wrapped into UDP packets.

For a UDP/IP Ethernet device, one channel is used for Ethernet data transfer, for local as well as for remote communication. ‘Local’ means communication within a local, secure IP network, whereas ‘remote’ means communication outside the secure IP network, typically on the Internet, through NAT routers. A default UDP Port number (34378) is reserved for local communication, and another (34379) for remote. All remote P-NET communication must include a password, to protect the device from unauthorized access. The network administrator should set up the NAT router to transfer packets to the remote communication UDP Port only. If this is done, only P-NET packets including a correct password will be accepted if they come from the NAT router, whereas P-NET packets from the local, secure IP network are accepted without password.

In general, it is recommended to use only a switched network, to reduce collisions, and to eliminate the time taken by P-NET nodes for rejecting packets intended for other nodes in a network. To completely avoid collisions, select Full Duplex. As auto negotiation to 10 MBit, Full Duplex is not possible, managed switches must be used, and manually configured.

Furthermore, it is recommended to use a separate IP subnet for P-NET nodes. P-NET devices with a UDP/IP Ethernet Communication Channel are set up to the default IP subnet address 172.17.17.xx. The subnet mask is fixed at 255.255.255.0. There are two ways of enabling a PC to communicate on this subnet: Either in the Advanced TCP/IP setup window in the control panel, add a new IP address (for example 172.17.17.10), or set up a local router to route packets to subnet 172.17.17.xx. Any other subnet address can be used, and is easily configured by means of the “Set P-NET Node Address” feature in VIGO.

Every server in a P-NET UDP/IP network must have a fixed IP address, and does not use DHCP. Normally, P-NET devices with a UDP/IP Ethernet Communication Channel have the IP address 172.17.17.NA, where NA is the P-NET Node Address. When the P-NET Node Address is set (for example by means of the Set P-NET Node Address utility in VIGO), the complete IP address is automatically set too. The P-NET Node address of a server can be in the interval 1..125. 0 is illegal, and 126 and 127 are used for netcast (broadcast within IP subnet).

A NetIndex and a NodeAddress form the address of a node in a P-NET UDP/IP network. The NetIndex selects the subnet, to which the node is logically connected, and the NodeAddress selects the node on that net. Up to 124 different subnets can be configured in the IPNetTable of the Ethernet communication channel. Subnet number 125 is reserved for dynamic client nodes. A subnet can be of type IPRange or UDPRange.

On an IPRange subnet, the first 3 bytes of the IP address come from the IPNetTable entry selected by the NetIndex, and the last byte from the NodeAddress. Example: IPNetTable[24] is an IPRange subnet, with IP address 172.18.19.00. The server logically connected to this subnet, with NodeAddress 12 is addressed with NetIndex = 24, NodeAddress = 12. IPRange subnets are used for direct addressing of nodes, without going through NAT routers. The same UDP port number is used to address all nodes on the same IPRange subnet. The UDP port number is defined in the IPNetTable. The value is typically 34378.

On a UDPRange network, the complete IP address comes from the IPNetTable entry selected by the NetIndex. The NodeAddress is added to the UDPPort defined in the IPNetTable entry. This configuration is used to access nodes on a remote network, through a NAT router. The IPAddress of the UDPRange subnet is the IPAddress exposed to the Internet by the remote NAT router. The router must be configured to translate the incoming UDP port number into the IPAddress of the node to be accessed, and to UDP port number 34379. A separate UDPRange subnet must be used for each remote network to be accessed.