Dynacord DPM 8016 Operation Manual Download Page 35

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Appendix

Ethernet basics

The DPM 8016 system controller can be connected to an Ethernet connection via the Ethernet
interface (RJ-45) on the rear panel. Ethernet is a computer networking technology for local
networks. If two devices (hosts) are to be connected, they can be connected via a crossed
Ethernet cable (crossover cable). If more than two devices are to be connected, they are
connected via a normal Ethernet cable (patch cable) and a central node (hub or switch). The
central node has one connection (port) for each participant on the network. The Ethernet
interface of the DPM 8016 is compatible with the following Ethernet standards:
•

10Base-T (IEEE 802.3i): With this standard, four wires (two twisted pairs) of a CAT-3 or
CAT-5 cable are used for the connection. The transfer rate is 10 Mbit/s, and the maximum
length of a segment is 100 meters.

•

100Base-TX (IEEE 802.3u): As with 10Base-T, two twisted cable pairs are used, but a
CAT-5 cable must be used. 100Base-TX with a transfer rate of 100 Mbit/s is the standard
Ethernet implementation.

IP address
Different network protocols can be used for communication between the devices connected
to the Ethernet. The DPM 8016 uses the TCP/IP protocol, which means this is an IP network.
In an IP network, IP addresses are used for the logical address assignment of devices. The
DPM 8016 uses version IPv4 (Internet Protocol Version 4) for address assignment, which
means an IP address is 32 bits (= 4 bytes) long. Using this system, around 4.3 billion unique
addresses are possible in theory. IPv4 addresses are usually represented using dotted decimal
notation, i.e., the four bytes are written as four decimal numbers separated by decimal points.
The general format of an IPv4 address is therefore AAA.BBB.CCC.DDD, for example
130.009.122.195. Leading zeros can also be omitted, so that the above example can also be
written as 130.9.122.195. The following table shows address ranges that should be used in
private networks. Private IP addresses are particularly useful in networks that are connected
to the Internet. Private IP addresses are not routed in the Internet, which means that an
address conversion with NAT (Network Address Translation) or PAT (Port Address Translation
= NAT and additional change of the port number) is necessary to access the Internet. This
means that several devices can be connected to the Internet via a router even if only one IP
address has been assigned by the Internet provider. It also means that the real IP addresses of
the devices can be hidden from hackers by NAT/PAT (security through obscurity).
Subnet mask
An IP address is always subdivided into a network element (network address/ID) and a host
element (host address/ID or device address). Devices are in the same IP network if the
network elements of their addresses are identical. If devices are in the same IP network, they
can communicate with each other directly. In order for devices in different networks to
communicate, additional equipment (such as a router) is required. Host addresses may not be
duplicated within a network. For example, a network could split the 4 bytes (32 bits) of an IP
address into a 3 byte network element and a 1 byte host element. The precise split between
the network element and host element is given in the form of a subnet mask. In this case, the
subnet mask 255.255.255.0 would mean the IP address was split into the first 24 bits or last 8
bits. The CIDR notation for displaying a subnet mask was an alternative to dotted decimal
notation. In CIDR notation, suffixes are used. The suffix specifies the number of 1-bits in the
subnet mask. The subnet mask 255.255.255.0 in dotted decimal notation would therefore