Envoy Configuration and Management Manual

Introduction to Envoy
Envoy Configuration and Management Manual—429861-001
2-6
Point-to-Point Data Links
For more information about communication protocols, profile disk file names, device
types and subtypes, and line types, refer to Profiles and Associated Protocols
on
page 3-1.
Point-to-Point Data Links
The simplest networks consist of one or more computers and/or terminals connected by
individual communications lines to a remote computer. Each such machine-to-machine
connection is a point-to-point data link, and each computer or terminal is a station in the
overall network. The application programs in the various computers address each remote
station implicitly by directing their read and write operations to the appropriate
communications lines.
In a point-to-point data link, the local station and the remote station are connected by
either a switched or a nonswitched line.
In a switched-line configuration (Figure 2-2
), the electrical connection between the two
stations exists over the public data network (PDN). Each station has its own telephone
number; to establish a connection, one station dials the other’s number. When the
stations finish communicating with one another, they terminate the link.
A switched line sometimes is called a dial-up connection, because a temporary
connection is established when one station dials the other station's number.
Table 2-1. Protocols, Line Configurations, and Concentrator Types
Protocol Line Configuration Concentrator Type
ADM-2 Multipoint supervisor Asynchronous*
Asynchronous Generalized supervisor Asynchronous
BISYNC (IBM, BSC) Multipoint (supervisor or tributary) Byte-synchronous
BISYNC (IBM, BSC,
SWIFT)
Point-to-point (primary or
secondary)
Byte-synchronous
Burroughs Point-to-point (primary or
secondary)
Asynchronous or Byte-
synchronous
Full Duplex Point-to-point Byte-synchronous
TINET Multipoint supervisor Asynchronous
* Envoy also supports Burroughs multipoint configurations, using either the asynchronous
or byte-synchronous concentrator. Burroughs multipoint asynchronous lines are configured
as ADM-2 lines. Burroughs multipoint byte-synchronous lines are configured as regular
BISYNC multipoint supervisor lines.