Digital Data Communication Message Protocol

DDCMP (Digital Data Communication Message Protocol) is a byte-oriented protocol for synchronous and asynchronous point-to-point connections. It was designed by Digital Equipment Corporation as a link layer of DECnet. 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 DDCMP 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 DDCMP on a variety of high-speed SBus, VMEbus and PCI intelligent communication controllers.

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

Features.

• Conforms to Digital Equipment Corporation's specification for DDCMP.
• Supports multiple serial lines, which are independently configurable for synchronous or asynchronous operation, line speed, clock source, message size, timeouts and more.
• 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 DDCMP messages 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.

DDCMP 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 DDCMP, UconX uses a subset of the Data Link Provider Interface (DLPI), which defines a STREAMS-based message interface between a data link service provider (DDCMP) 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 DDCMP:

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

Requests transmission of a STACK.

DL_GET_STATISTICS_REQ

Requests connection statistics.

DL_DATA_REQ

Contains a DDCMP data message for transmission.

The following primitives are sent from DDCMP 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 receipt of a STACK.

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 DDCMP data message.

Statistics.

At any time, a client application can request statistical and state information for its DDCMP connection. Reported statistics include counts of transmitted and received messages, separated by message type; current state of the connection; and current transmitted and received sequence numbers.

Configuration Parameters.

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

• Synchronous or asynchronous operation.
• Conformance with DDCMP version 4.0 or I2.
• Values for T1 and N2.
• Time to wait before sending a delayed acknowledgement.
• Maximum number of data messages received before sending an acknowledgement.
• Maximum number of unacknowledged data messages to send.
• Maximum data message size.
• Line speed or external clocking.
• Parity and stop bits (for asynchronous operation only).

Line Monitor.

The UconX DDCMP product includes a unique Line Monitor feature that can be used at any time for diagnostic purposes. UconX supplies a sample monitor application which displays information about data traffic on a serial link in an easy-to-read format. The information displayed for each DDCMP message includes direction (transmit or receive), message type, address, flags, sequence numbers and more.

The first time you set up 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 .