6100 ADCCP Programming Manual

3 ADCCP/X21 Protocol Module
069225 Tandem Computers Incorporated 3–1
X.21 is a CCITT recommendation that specifies the physical and functional interface
between data terminal equipment (DTE) and data circuit-terminating equipment
(DCE) for synchronous operation on circuit-switched public data networks. This
interface is defined in the CCITT Recommendation X.21 of 1980 and 1988.
X.21 networks provide either circuit-switched or leased connections between host
systems. Once an X.21 connection is set up, the network passes user data
transparently between the endpoints. The X.21 network does not impose a packet or
any other structure on the bit stream while a connection is established.
Features of
ADCCP/X21
ADCCP/X21 provides an X.21 call-control interface within the ADCCP protocol
module. ADCCP/X21 is downloaded into a 3650/6100 CSS or 3605/6105
communications controller, where it is executed by microprocessor circuitry in an X.21
LIU. The X.21 LIU consists of a CLIP 1 connected to an X.21 LIM. The ADCCP/X21
module is stored as a disk file and downloaded into the CLIP’s RAM when the system
is cold loaded or by operator request.
ADCCP/X21 allows your application to set up an X.21 circuit-switched connection
and then communicate over the circuit using the ADCCP bit synchronous
communication line protocol. The features of ADCCP/X21 lines allow your
application to:
Make different types of outgoing call requests. Depending on the call control
features provided by your X.21 network, an application can make the following
types of calls:
Normal calls using either full or abbreviated addressing
Direct calls
Selective direct calls
Accept incoming calls.
Transfer data over either a switched or leased X.21 network connection. (The
maximum is 64 K bits per second.)
Determine the action that ADCCP/X21 takes for each class of call progress signal.
Automatically retry certain types of unsuccessful calls.
Deliver the following information to your application:
Identification of the calling station when a call request comes in from the
network
Identification of the called station when a connection request that you have
made has been accepted
Charging information for the call after an X.21 connection has been cleared