HDLC NRM is a bit-oriented protocol for half- or full-duplex point-to-point or multipoint links. This data link control protocol operates in an unbalanced mode, with a primary station at one end of the data link and one or more secondary stations at the other end. The HDLC NRM protocol provides flow control and error detection, and guarantees the accurate exchange of information across the physical interface.

UconX Corporation has implemented the HDLC NRM 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 NRM on various high-speed SBus, VMEbus and PCI intelligent communication controllers.

A single server or controller can support HDLC NRM 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 NRM on others.

Features.

• Conforms to ISO 3309, 4335 and 7809 specifications.
• Conforms to ANSI X3.66, American National Standard for Advanced Data Communication Control Procedures (ADCCP) in Normal Response Mode (NRM).
• Supports multiple serial lines, which are independently configurable for line speed, clock source, frame size, timeouts and other options.
• Each serial line can be configured to support operation as a primary (control) station or to support one or more secondary (tributary) stations.
• Supports two-way alternate (half-duplex) and two-way simultaneous (full-duplex) operation.
• HDLC NRM optional functions are selectable for each individual station. Supported options include 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 NRM 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 NRM, UconX uses a subset of the Data Link Provider Interface (DLPI), which defines a STREAMS-based message interface between a data link service provider (NRM) 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 NRM:

DL_ATTACH_REQ

Assigns and configures a serial link

DL_DETACH_REQ

Frees a previously attached serial link

DL_BIND_REQ

Assigns and configures a station on a serial link

DL_UNBIND_REQ

Frees a previously bound station

DL_CONNECT_REQ

Brings the connection to normal response mode

DL_DISCONNECT_REQ

Returns to normal disconnect mode

DL_GET_STATISTICS_REQ

Requests connection statistics

DL_DATA_REQ

Contains data to be sent in one or more HDLC frames

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

DL_BIND_ACK

Indicates successful completion of DL_BIND_REQ

DL_OK_ACK

Acknowledges miscellaneous request types

DL_ERROR_ACK

Reports unsuccessful completion of a request

DL_CONNECT_CON

Indicates good completion of DL_CONNECT_REQ

DL_CONNECT_IND

Reports a transition to normal response mode

DL_DISCONNECT_IND

Reports a disconnect condition

DL_GET_STATISTICS_ACK

Provides data transfer statistics

DL_DATA_IND

Contains data received in an HDLC frame

Statistics.

At any time, a client application can request statistical and state information for its HDLC NRM 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.

The UconX HDLC NRM software package includes a background client process that auto-configures serial links based on parameters read from a text file. Each serial link can be individually configured with the following options:

• Primary or secondary operation
• Two-way alternate or two-way simultaneous operation
• Values for T1 and N2
• The rate at which secondary stations are polled
• Time to wait before transmitting a delayed RR
• Maximum number of frames received before sending RR
• Maximum number of unacknowledged frames to send
• Maximum size of HDLC frame
• Line speed or external clocking
• Use of CTS and DCD modem signals
• For each individual station on a serial link, the use of Reject, Selective Reject and unnumbered information frames can be enabled or disabled, and the station address can be configured.

Line Monitor.

The UconX HDLC NRM 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 NRM 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 Joseph Dohn at (619) 627-1700 or email us at sales@uconx.com . For technical questions about our products, please email us at tech@uconx.com .