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Gateways
The Annotator 300 can communicate with the e-mail server that it uses for e-mail
notification directly (if they are on the same subnet), or the communication can be routed
via a gateway (a computer that provides a link between different subnets).
Local and remote devices
The local and remote devices are defined from the point of view of the function being
described. In this manual, subnetting is an issue when you are using the controlling PC to
set TCP/IP values in the Annotator 300.
IP addresses and octets
Valid IP addresses consist of four 1-, 2-, or 3-digit numeric subfields, properly called
octets, which are separated by dots (periods) (figure 61). Each octet can be numbered
from 000 through 255. Leading zeros, up to 3 digits total per octet, are optional. Values of
256 and above are invalid.
192.168.254.254Typical IP Address:
Octets
Figure 69. IP Address and Octets
Subnet masks and octets
The subnet mask (figure 62) is used to determine whether the local and remote devices
are on the same subnet or different subnets. The subnet mask consists of four numeric
octets separated by dots. Each octet can be numbered from 000 through 255. Leading
zeros, up to 3 digits total per octet, are optional. Each octet typically contains either 255
or 0. The octets determine whether or not the same octets of two IP addresses will be
compared when determining if two devices are on the same subnet.
255.255.0.0Typical Subnet Mask:
Octets
255 indicates that this octet will be
compared between two IP addresses
.
0 indicates that this octet will not be
compared between two IP addresses
.
Figure 70. Subnet Mask and Octets
Determining whether devices are on the same subnet
To determine the subnet, the local device’s IP address is compared to the remote device’s
IP address (figure 63 below). Each address’s octets are compared or not, depending on
the value in the related subnet mask octet.
• If a subnet mask octet contains the value 255, the related octets of the local device’s
address and the remote device’s IP address are unmasked.
Unmasked octets are compared (indicated by ? in the figure below).
• If the subnet mask octet contains the value 0, the related octets of the local device’s
and remote device’s IP addresses are masked.
Masked octets are not compared (indicated by X in the figure below).
If the unmasked octets of the two IP addresses match (indicated by = in the figure below,
example 1), the two addresses are on the same subnet.
If the two unmasked fields do not match (indicated by an unequal sign in the figure below,
example 2 and example 3), the addresses are not on the same subnet.
Annotator 300 • Ethernet Connection 103