Legacy Data System Reference - Comtech EF Data

Legacy Data
5.1 NetPerformer Support of Asynchronous Data Traffic
The NetPerformer supports two asynchronous communication modes on a serial port:
• Reliable mode (R-ASYNC)
• Transparent mode (T-ASYNC).
The ASYNC (Asynchronous communications) driver has the following characteristics:
• Configurable character format of 7 or 8 bits.
• Configurable parity bit (NONE, EVEN, ODD, SPACE MARK, IGNORE,
2STOP).
• Two types of flow control (XON-XOFF, HARDWARE).
• Error detection using the parity bit.
Characters received are forwarded to the compressor in cells of at least 1 byte and at most
48 bytes. At the remote site, the composite link information is decompressed and passed to
the transmitter which then transmits the data as it is received.
5.2 R-ASYNC Mode
In Reliable mode (R-ASYNC), cells are forwarded to a proprietary level 2 protocol before
being sent over the composite link. This protocol ensures retransmission in case of errors
on the link. The NetPerformer provides two flow control methods when the port is
configured Reliable mode: XON-XOFF and HARDWARE (CTS/DSR). This guarantees
that the buffers will not overflow and loose data.
5.3 T-ASYNC Mode
In Transparent mode (T-ASYNC), all characters received on a user port are transmitted on
the composite link without any interpretation. If an error occurs on the composite link
while characters are being transmitted, these characters will be lost.
The Transparent mode supports link-level asynchronous protocols. These protocols, like
DDCMP/ASYNC, XMODEM or POLL-SELECT/ASYNC, automatically retransmit
frames in case of errors or timeouts. If the NetPerformer port is configured in Reliable
mode for these protocols, multiple retransmissions could occur if both the NetPerformer
and the connected device start to retransmit data.
5-2 Memotec Inc.