Specifications

54
HDLC Programming Library
What is HDLC?
High-Level Data Link Control (HDLC) standard is so far
one of the most widely used synchronous data link control
protocol. HDLC is a group of protocols or rules for
transmitting data between network points (sometimes
called nodes). In HDLC, data is organized into a unit (called
a frame) and sent across a network to a destination that
verifies its successful arrival. The HDLC protocol also
manages the flow or pacing at which data is sent. HDLC is
a bit-oriented line protocol specification, corresponding
to Layer 2 (Data Link Layer) of Open Systems
Interconnection (OSI).
Why is HDLC important?
The HDLC protocol has been used as a basis for the
development of a number of other widely used link layer
protocols. These protocols illustrate the importance of
HDLC in developing modern network applications. As
the figure shows, HDLC applications(in green columns)
are applied in various fields of technologies or network
layers(orange columns). Each of these protocols is a
derivation of HDLC and uses various combinations of
HDLC features with own protocol-specific operations. By
knowing HDLC, one can easily grasp basic operations of
the widely used protocols derived from HDLC.
How to develop HDLC?
MOXA multiport sync board products provide easy-
programming Sync API for DOS, Windows 3.x and
Windows NT environment and cover C/C++, Visual Basic,
and Delphi languages. MOXA Sync API provides physical
layer interface for HDLC, therefore programmers do not
have to consider bit sync details. Comprehensive API
functions are also helpful for developing higher level of
protocols or applications. MOXA Sync API is based on
easy-to-use DOS concepts for developing multi-task
functions of Windows NT, bringing users the true handy
tool for sync application development.