Envoy ACP/XF Configuration and Management Manual

Introduction to EnvoyACP/XF
EnvoyACP/XF Configuration and Management Manual—429232-003
2-5
Multipoint Data Link
Multipoint Data Link
A somewhat more complex network consists of several terminals or computers
connected in parallel to a single communications line. This configuration is a multipoint
data link; each terminal or computer is a station in the network.
In a multipoint data link (Figure 2-5), one station is the supervisor. The supervisor
controls all communications over the link; all other stations are tributaries.
Communication can occur only between the supervisor and a tributary; tributary-to-
tributary communication is not permitted. Each tributary has a unique station address
that is defined at the application level in both the supervisor and the individual
tributaries. Transmissions between the supervisor and a tributary (in either direction)
always contain the particular tributary’s station address.
To solicit data transfers from the tributary stations, the supervisor periodically polls
each tributary station in the multipoint link. A tributary station cannot transmit data until
it is polled.
Figure 2-4. Point-to-Point Nonswitched Line
VST006.vsd
Privately Owned Cable or
Nonswitched Line
Station Station