Envoy ACP/XF Application Programming Manual

Normal Response Mode (NRM) Protocols

EnvoyACP/XF Application Programming Manual–132179

3-8

Timers and Number of Retries

SDLC and ADCCP each maintain two retry count variables: one for the RR frame

transmissions and one for the I-frame retransmissions. EnvoyACP/XF uses the retry-

count parameter for both RR frame and I-frame retransmissions. If the remote station

responds to an RR frame, the local station does the following:

1. Resets the RR frame retry count to 0.

2. Retransmits the I-frame.

3. Increments the I-frame retry count.

The I-frame retry count resets to 0 either when the remote station acknowledges the I-

frame or when EnvoyACP/XF aborts the WRITE operation because one of the retry

counts is exhausted. Figure 3-2

shows the use of timeouts and these two retry variables.

Figure 3-1. T1TIMER and RR Frame Retry Count

Retry Count = 3

WRITE Operation Issued

Send I-Frame,P

Send RR,P

(No Response; Timeout)

WRITE Operation Aborted with File-System Error Code 162.

Send RR,P

RR Frame

Retry Count

017