Installation guide

Network Infrastructure for EtherNet/IP™
D-4
Appendix D Glossary of Terms
Term Definition
segment A collection of nodes connected to an uninterrupted section of
physical media.
Simple Network Management Protocol (SNMP) A standard protocol used to monitor nodes, switches, routers,
and networks to which they are attached.
Spanning Tree Protocol (STP) A switch (or bridge) protocol that uses the spanning-tree
algorithm, enabling a switch to dynamically work around loops
in a network topology by creating a spanning tree. Switches
exchange special messages with other switches to detect loops,
and then remove the loops by shutting down selected switch
interfaces. Refers to both the IEEE 802.1D Spanning-Tree
Protocol standard and the earlier Digital Equipment Corporation
Spanning-Tree Protocol on which it is based.
subnet A collection of nodes using a common protocol and shared
media access arbitration. Subnets may have multiple physical
segments and contain repeaters.
system Contains one or more domains.
target A destination for I/O connection or message requests. It can
only respond to a request (not initiate an I/O connection or
message.)
Time to Live (TTL) A technique used in best-effort delivery systems to avoid
endlessly looping packets. For example, each IP packet is
assigned an integer TTL when it is created (TTL is a field in the
IP packet header). Each router decrements the TTL field when
the packet arrives. A router discards any packet when TTL
reaches zero.
unicast A transmission method by which a packet is sent to a single
destination. All TCP packets are sent via unicast on EtherNet/IP.
Virtual LAN (VLAN) A group of devices on one or more LANs that is configured
(using management software) such that the devices can
communicate as if they were attached to the same wire, when in
fact they are located on a number of different LAN segments.
Because VLANs are based on logical as opposed to physical
connections, they are extremely flexible.
References
1 Comer, Douglas E., Internetworking with TCP/IP, Volume 1: Principles, Protocol, and Architecture,
Prentice Hall, 1995.
2 Dictionary of Internetworking Terms and Acronyms, available on www.cisco.com