18 August 1998
DATA TRANSMISSION SYSTEMS
UMCS DATA TRANSMISSION TOPOLOGIES.
a. UMCS data transmission networks are defined as peer-to-peer networks where all nodes (island
station computer, workstations and field equipment panels) have the same level of control over the
communications and can control their own activities. In the UMCS, peer-to-peer network data is stored in
many locations (distributed processing) and the island station computer takes the role of a server. UMCS
network topology describes the physical layout of the data transmission system. UMCS data transmission
system topologies include the following.
Point-to-point is a dedicated connection between two devices.
(2) Bus topology is a form of multinode local area network (LAN) data transmission system. In
a bus network all the devices connect directly to the same media by means of connectors in a daisy
chain configuration. Bus LANs include token-passing LANs and ethernet LANs which utilize carrier sense
multiple access/collision detection.
(3) Star topology is a configuration in which the UMCS island station computer or a
communications hub connects radially to multiple field equipment panels. Star topologies include token
ring, where the ring is internal to a multistation access unit, and hub ethernet, which is also called 10
(4) Hybrid topologies (combination bus and star) are used in an arcnet network, which is a
b. The UMCS data transmission system is also defined by the data transmission media used.
Guided or physical media consists of fiber optics, wireline and coaxial cable. Unguided media consists of
one-way radio frequency (RF) or two-way RF packet transmissions.
c. The selection of UMCS data transmission system topology will be based on the size of the
system. Arcnet-based networks are limited to 256 nodes. Ethernet-based networks can be extended
over 1000 nodes based on addressing capabilities, but the practical number is much lower because the
collision detection nature of ethernet will limit network performance as the network size grows. The use
of 10 Base-T hubs and multiple network segments can improve ethernet performance.
d. Data transmission between smart field panels and remote terminal units, universal programmable
controllers or unitary controllers typically uses a bus topology.
e. Network interconnection devices, including hubs, bridges and routers, extend or interconnect
networks or network segments.
(1) Active or passive hubs provide a central location for the connection of cables from network
devices such as field equipment panels, workstations, and other hubs. Active hubs regenerate signals
between devices connected to them. Passive hubs pass the signals from one port to the next without
signal conditioning or regeneration.
(2) Bridges provide a communication path between two or more network segments. Bridges
enable devices on one network segment to communicate with devices on another network segment.
Bridges allow only those packets destined for the other network segment to be passed.