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xtproto(M)

xtproto -- multiplexed channels protocol used by xt(HW) driver

Description

The xt(HW) driver contains routines which implement a multiplexed, multi-buffered, full-duplex protocol with guaranteed delivery of ordered data via an 8-bit byte data stream. This protocol is used for communication between multiple UNIX system host processes and an AT&T windowing terminal operating under layers(C).

The protocol uses packets with a 2-byte header containing a 3-bit sequence number, 3-bit channel number, control flag, and data size. The data part of a packet may not be larger than 32 bytes. The trailer contains a CRC-16 code in 2 bytes. Each channel is double-buffered.

Correctly received packets in sequence are acknowledged with a control packet containing an ACK; however, out of sequence packets generate a control packet containing a NAK, which will cause the retransmission in sequence of all unacknowledged packets.

Unacknowledged packets are retransmitted after a timeout interval which is dependent on baud rate. Another timeout parameter specifies the interval after which incomplete receive packets are discarded.

Files

/usr/include/sys/xtproto.h channel multiplexing protocol definitions

See also

layers(M), layers(C), xt(HW)
© 2003 Caldera International, Inc. All rights reserved.
SCO OpenServer Release 5.0.7 -- 11 February 2003