GE GFK-1541B - Manual (Page 201)

A-8 TCP/IP Ethernet Communications for the Series 90™ PLC User's Manual – May 2002 GFK-1541B
A
supervisory access to the Ethernet Interface. The Station Manager may be accessed locally
via the serial port, or remotely over the LAN.
Stratum The number provided by an SNTP server that indicates the server’s relation to a “true”
time source. The lower the stratum number, the closer that particular SNTP server is to a
“true” time source. A “true” time source is usually based on an atomic clock such as the
broadcast signal transmitted by the Naval Observatory or GPS (Global Positioning System)
satellite signals. If configured for SNTP synchronization, Series 90 Ethernet Interfaces
automatically synchronize to the SNTP server with the lowest stratum number.
Subnet, Subnet Id, Subnet Mask The subnet mask is a mechanism to logically divide a large
network into smaller subnets according to your local assignment of IP addresses to nodes on
the network. Nodes on the network which have their IP addresses alike for the bits specified
in the subnet mask can talk to each other directly; nodes whose IP addresses are not alike in
these same bits must talk indirectly, via an intermediate gateway or router.
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 further information, refer to Chapter 5, “Network Administration
Support”.
Tally Counters kept by the LAN Interface to indicate load and performance information.
TCP/IP Commonly refers to the entire suite of protocols that run over IP. Includes, but is not
limited to IP, TCP, ARP, UDP, ICMP, and IGMP.
Time Synchronization The ability to synchronize the internal time clock of an Ethernet Interface to
time signals from a remote time server on the network. Time synchronization is useful in
conjunction with Ethernet Global Data.
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 Control Protocol (TCP) The Internet standard connection-oriented transport
level protocol. (See also Internet Protocol (IP).)
Transmission Path Delay The time required for a bit to travel between the two most distant
network nodes in a bus network.
Unicast. The transmission scheme in which exactly one receiver is specified as the target of a
transmission.
Universal Address Administration See Global Address Administration.
User Datagram Protocol (UDP) The Internet standard connectionless transport level protocol.