Envoy Configuration and Management Manual

Introduction to Envoy
Envoy Configuration and Management Manual—429861-001
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Point-to-Point Data Links
A nonswitched line (Figure 2-3), on the other hand, provides a permanent path between
stations. This path can be a privately owned cable (often the case when a terminal is
connected to a computer) or a dedicated path leased from a common carrier, such as the
public telephone network. The terms nonswitched and leased are used interchangeably
when describing line facilities. In a nonswitched line, a station need not dial a number to
establish a call; a permanent link exists between stations.
In a point-to-point configuration, when a station wishes to transmit data it first bids for
the use of the line by sending an enquiry (ENQ) control character. To resolve contention
for the line (two stations bidding simultaneously), one station is designated as the
primary and the other as the secondary. If contention for the line exists, the secondary
station always defers to the primary station.
A full-duplex line protocol permits two stations to transmit and receive simultaneously.
Figure 2-2. Point-to-Point Switched Line
Modem
Station A
Station
B
Station C
Public Data
Network
CDT005.CDD
Modem