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TCP/IP Ethernet Communications User’s Manual - August 1997 GFK-1084B
As described in an appendix to your Ethernet module user manual, the 32 bits of an
IP address are divided between a net id part and a host id part. (The class of the IP
address determines how many bits are in the net id and how many are in the host id.)
In general, the net id portion of the IP address (on the left) is assigned by the Internet
authorities. The host id portion (on the right) is assigned by your local network
administrator. Subnetting is locally optional and consists of designating some (any
number) of the host id bits as an extended net id, or subnet id. The added subnet id bits
are normally taken from the host id bits adjacent to the net id, and the subnet mask
identifies these bits. In your Ethernet module configuration, you specify these bits
as one (1) and the remaining host id bits as zero (0). For example:
IP Address: 11.22.33.44
Net Id bits: 255.0.0.0 Net Id: 11.0.0.0
Added Subnet Id bits: 0.255.0.0 Subnet Id: 0.22.0.0
Subnet Mask: 255.255.0.0 Extended Net Id: 11.22.0.0
All nodes on a subnetted network must use the same value for subnet mask; subnets
are distinguished by different subnet ids, created by your local assignment of IP
addresses.
For further information, refer to the appendix titled Advanced Information About IP
and MAC Addresses in your Ethernet module user manual.
Station Manager A part of the basic Ethernet Interface communications software that
executes as a background activity on the Ethernet Interface. The Station Manager
provides interactive supervisory access to the Ethernet Interface. The Station
Manager may be accessed locally via the serial port, or remotely over the LAN.
Tally Counters kept by the LAN Interface to indicate load and performance information.
Topology The pattern formed by the physical medium interconnecting the nodes of a
network.
Transceiver See Medium Attachment Unit (MAU).
Transceiver Cable See Attachment Unit Interface (AUI).
Transmission Path Delay The time required for a bit to travel between the two most
distant network nodes in a bus network.
Transmission Control Protocol (TCP) The Internet standard connection-oriented
transport level protocol. See also Internet Protocol (IP).
Universal Address Administration See Global Address Administration.
Word A measurement of memory length, usually 4, 8, 16, or 32 bits long. In the Series
90 PLC, a word is always 16 bits.