15
Network Interface
(MiniPlex-2E, MiniPlex-2Wi)
A network interface connects the multiplexer directly to a network with possibly more than one device.
There can be more than one multiplexer connected to a network and/or more than one device that needs
to communicate with a multiplexer.
Network Basics
In order to understand how a networked multiplexer works and how to connect to it, it is necessary to
know a little bit about IP addresses, port numbers and protocols.
IP Address
Every device on a network needs a unique number to be able to identify that device. This allows us to
send a message to one single device on a network. These unique numbers are called MAC addresses and
every device in the world that is connected to a network has a unique MAC address. The MAC address of
a MiniPlex-2E or -2Wi multiplexer is printed on the serial number label and looks like
00-20-4A-E4-28-58
These addresses are a bit cryptic and not easy to work with. Therefore a mechanism is used to assign a
more easy to read number to a device, called an IP address. An IP address consists of four numbers
grouped together, separated by dots. Each number can range from 0 to 255. An IP address looks like
this:
192.168.1.45
Assigning an IP address to a device could be compared to sticking a coloured label to your house. Now
the postman only needs to remember the colour of your label instead of your complete address. Of
course, someone needs to manage a list that matches the colour to your address in order to prevent two
houses of receiving the same coloured label. Networks and network devices have mechanisms built in
that take care of this so we don’t have to worry about it (it’s called ARP or Address Resolution Protocol).
Netmask
Another tricky bit of networking is a netmask. A netmask basically determines which part of an IP
address is the network address and which part is the device address. In its most basic form, a netmask
consists of four numbers, similar to an IP address, that are either 255 or 0. And the 255’s always come
first. A device always has an IP address AND a netmask, for instance:
192.168.1.45 and 255.255.255.0
This combination of IP address and netmask tells us that the first three numbers of the IP address are
the network address (192.168.1) and the fourth (45) is the device’s address. It also means that this
particular combination limits the number of devices on this network to 254 (0 and 255 are reserved).
A network address allows us to send a single message to all devices on the network, instead of sending it
to one single device. This is called a
broadcast
(see below). In this example, the broadcast address is
192.168.1.255. The last number here is 255, which means that it targets all devices on the network.
If we have an IP/netmask combination of 192.168.1.45/255.255.0.0, it means the network address is
192.168 and the device’s address 1.45, that there are 65534 possible devices (0.0 and 255.254 are
reserved) and that the broadcast address is 192.168.255.255.
If you’re completely lost at this point, don’t worry. Just remember two things:
•
all devices on a single network must have the same netmask
•
all devices on a single network must have the same network address
So when the netmask for example is 255.255.255.0, the first three numbers of the IP addresses must be
the same.
Port Number
A port number can be seen as a sub address within one single device. When a message is sent over the
network, it always contains the IP address of the sender, the IP address of the receiver and a port
number. This port number is just a logical number that determines the type of data in the message.
Web servers for instance, always listen to messages that have port number 80. If you start your web
browser and enter the name of a web site, the request to show the contents of a page is sent to a web
server using port number 80. Similarly, your mail program always uses port number 110 to retrieve mail
from a mail server and port number 25 to send mail to a mail server.
