HDLC ABM

HDLC ABM is an efficient, bit-oriented protocol for full-duplex, point-to-point links. This data link control protocol provides flow control and error detection, and guarantees the accurate exchange of information across the physical interface.

UconX Corporation has implemented the HDLC ABM protocol in a client-server environment using the UconX family of LAN-based, multi-protocol communication servers. The UconX server attaches to your local area network to provide wide-area connectivity for all clients on the LAN.

UconX also supports HDLC ABM on a variety of high-speed SBus, VMEbus and PCI intelligent communication controllers.

A single server or controller can support HDLC ABM operation on multiple serial links. Or, you can run other UconX protocols, such as X.25 or Asynchronous Data Transfer, on some links and HDLC ABM on others.

Features.

• HDLC ABM can be configured for HDLC LAPB, which provides the frame level of X.25 (CCITT X.25 Level II).
• Conforms to ISO.
• IEC specifications 3309, 4335 and 7809.
• Conforms to ANSI X3.66, American National Standard for Advanced Data Communication Control Procedures (ADCCP) in Asynchronous Balanced Mode (ABM).
• Supports multiple serial lines, which are independently configurable for line speed, clock source, frame size, timeouts and other options.
• HDLC ABM optional functions are selectable for each serial line. Supported options include extended addressing, extended sequence numbering, use of Reject, use of Selective Reject, and use of unnumbered information frames.
• Client software in source form includes an Application Programming Interface (API), sample application programs, and, for embedded communication controllers, a host device driver.
• LAN-based servers support UNIX and VMS client systems.
• Other UconX wide-area protocols can operate simultaneously on the same platform.
• Line Monitor diagnostic feature can be used to display all frames transmitted and received on any serial line.
• Data transmission and reception in loopback mode can be used to verify correct installation and hardware operation.

Client API.

HDLC ABM includes a simple, easy-to-use API to protocol software running on a LAN-based server or communication controller. The API provides a standard interface to the TCP/IP software or host driver. This makes application programs easily portable among client operating systems as well as the various UconX server and embedded controller platforms.

DLPI Interface Primitives.

For the interface to HDLC ABM, UconX uses a subset of the Data Link Provider Interface (DLPI), which defines a STREAMS-based message interface between a data link service provider (ABM) and an application program. Applications send and receive DLPI messages, or primitives, using the UconX API.

The following primitives are sent from the application to HDLC ABM:

DL_BIND_REQ

Assigns and configures a serial link.

DL_UNBIND_REQ

Frees a previously bound serial link.

DL_CONNECT_REQ

Brings the link to data transfer state.

DL_DISCONNECT_REQ

Disconnects an active connection.

DL_RESET_REQ

Resynchronizes the data link connection.

DL_GET_STATISTICS_REQ

Requests connection statistics.

DL_DATA_REQ

Contains an HDLC frame for transmission.

The following primitives are sent from HDLC ABM to the application:

DL_BIND_ACK

Indicates successful completion of DL_BIND_REQ.

DL_OK_ACK

Acknowledges various request types.

DL_ERROR_ACK

Reports unsuccessful completion of a request.

DL_CONNECT_CON

Indicates good completion of DL_CONNECT_REQ.

DL_DISCONNECT_IND

Reports a disconnect condition.

DL_RESET_IND

Reports resynchronization of the connection.

DL_RESET_CON

Indicates successful completion of DL_RESET_REQ.

DL_GET_STATISTICS_ACK

Provides data transfer statistics.

DL_TEST_IND

Provides Line Monitor information.

DL_DATA_IND

Contains a received HDLC frame.

Statistics.

At any time, a client application can request statistical and state information for its HDLC ABM connection. The protocol software maintains detailed counts of transmitted and received frames, separated by frame type; line errors, such as CRC errors and aborted frames; and other events, such as window-full conditions.

Configuration Parameters.

For each individual serial link, the UconX HDLC ABM software package allows configuration of the following parameters:

• DTE or DCE operation.
• Remote and local addresses.
• Values for T1, T3 and N2.
• Selection of optional functions (extended addressing, extended sequence numbering, use of Reject, use of Selective Reject, use of unnumbered information frames).
• Time to wait before transmitting a delayed RR.
• Maximum number of frames received before sending RR.
• Maximum number of unacknowledged frames to send.
• Maximum frame size.
• Line speed or external clocking.

Line Monitor.

The UconX HDLC ABM product includes a unique Line Monitor feature that can be used at any time for diagnostic purposes. To use this feature, an application program on a client system opens a special connection to HDLC ABM and specifies a serial link to be monitored. The protocol software records each frame as it is transmitted and received on the link, and sends the information to the client application. UconX supplies a sample monitor application which displays the received information in an easy-to-read format.

The information supplied for each HDLC frame includes direction (transmit or receive), frame type, address, and more.

The first time you attempt to establish a connection to a remote site, or any time you need to analyze problems with a particular connection, you can use this feature--instead of an expensive protocol analyzer.

Ordering Information: For more information or to place an order, please contact us at (619) 627-1700 or email us at sales@uconx.com . For technical questions about our products, please email us at tech@uconx.com .