Envoy ACP/XF Application Programming Manual

Normal Response Mode (NRM) Protocols

EnvoyACP/XF Application Programming Manual–132179

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Reject (REJ)

The REJ command or response indicates that the specified I-frame was received in error

and requests retransmission of the indicated I-frame and all subsequent I-frames. For

modulo-8 frame sequencing, this type of error recovery causes EnvoyACP/XF to

retransmit at most seven frames. For modulo-128 frame sequencing, however, the REJ

command or response can introduce substantial inefficiency. (For more information

about the REJ response, see S-Frame Command/Response Codes

on page B-7.)

Selective Frame Reject (SREJ)

The selective reject (SREJ) command or response indicates that the specified I-frame

was received in error and requests the retransmission of only that frame. EnvoyACP/XF

still must acknowledge succeeding I-frames. You can use SREJ with a basic control field

but always use SREJ with an extended control field. (For more information about the

SREJ response, see S-Frame Command/Response Codes

on page B-7.)

This type of error recovery is very efficient. For example: suppose you use an extended

control field (modulo-128 frame sequencing) and send 100 I-frames in succession. All

100 I-frames are received without error except frame #3. If the remote station uses the

SREJ command/response, you only need to retransmit frame #3. (By contrast, if the

remote station used the REJ command/response, you would need to retransmit 97 frames

— all but frames #0, #1, and #2.)

If SREJ is disabled, EnvoyACP/XF responds with a FRMR to any incoming SREJ

command.

If you set parameter 2.<0> = 0 within a tributary application, EnvoyACP/XF responds

with FRMR to any incoming SREJ commands.

If you set parameter 2.<0> = 0 within a supervisor application, EnvoyACP/XF ignores

any incoming SREJ commands. The commands are discarded, no response is sent, and

no error indication is posted.

You enable or disable the REJ command or response by using bit 7 of parameter 1 in a

SETMODE 16 call, as follows:

CALL SETMODE (fnum,16,parameter1,parameter2)

parameter1.<7> = 0: disable REJ command or response

= 1: enable REJ command or response

You enable or disable the SREJ command or response by using bit 0 of parameter 2 in a

SETMODE 19 call, as follows:

CALL SETMODE (fnum,19,parameter1,parameter2)

parameter2.<0> = 0: disable SREJ command or response

1: enable SREJ command or response

Initializing a Link

When your application interacts with SDLC or ADCCP-NRM lines, you may need to

download code from a primary station to a secondary station or from a supervisory

station to a series of tributaries. To set a secondary or tributary station to Initialization