D-4 Series 90™-30 PLC LONWORKS® Bus Interface Module User's Manual – June 1997 GFK-1322A
D
Channel Status Bits The Channel Status bits comprise bits 17–80 (64 bits) of the status
indication area. These bits consist of an error bit and a data transfer
bit for each of the channels that can be established
Client A node that requests network services from a server. A client PLC
initiates a communications request. (See also Server.)
Collision A condition that results from concurrent transmissions by two or
more nodes on the transmission medium.
Collision Domain A single CSMA/CD network. If two or more nodes are within the
same collision domain and both transmit at the same time, a collision
will occur. Nodes separated by a repeater are within the same
collision domain. Nodes separated by a bridge are within different
collision domains.
Command Dictionary Provides an alphabetical listing of the LAN Interface commands.
Command Field That part of a protocol data unit (PDU) that contains commands, as
opposed to the address field and information field.
Communications Window A part of the PLC scan that provides an opportunity for the LAN
Interface to read and write PLC memory. The window is executed
automatically once per PLC scan.
Connection A logical communication link established between two end points
and used to transfer information.
CSMA/CD See Carrier Sense Multiple Access with Collision Detection.
Data Communications Equipment
(DCE)
Examples: Modems and transceivers. Distinct from DTE, Data
Terminal Equipment.
Data Link Layer In Open Systems Interconnection architecture, the layer (Layer 2)
that provides services to transfer data over a physical link between
open systems. Consists of the LLC and MAC sublayers.
Data Terminal Equipment Examples: computers, terminals, printers. Distinct from DCE, Data
Communications Equipment.
DCS Words See Detailed Channel Status Words.
Detailed Channel Status Words Two status words containing detailed information on a single Series
90 channel. The DCS words are retrieved using the Retrieve Detailed
Channel Status Command.
Device Name A character string that identifies a particular communication
destination at a given network adapter ( for example, the PLC CPU
or an SNP gateway).
Directory Information Base (DIB) A collection of information used for directory services (like name
resolution). In this document DIB refers to the DDP database which
is actually distributed among all DDP devices instead of in a single
name server. (See also Distributed Directory Protocol (DDP).
Distributed Directory Protocol
(DDP)
The GE proprietary protocol used to provide distributed name
service on a TCP/IP Ethernet network. The distributed nature of
DDP means that there is no name server.
Domain Name System (DNS) The predominant name service protocol used by the Internet. DNS is
primarily used to resolve a name into an IP address.
Dotted Decimal The notation for IP, gateway, and name server addresses as well as
the subnet mask. It consists of 4 decimal numbers (0–255) separated
by periods. Example IP address: 3.0.0.1
Dynamic Host Configuration
Protocol (DHCP)
A superset of the BOOTP protocol (see BOOTP).
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