Envoy ACP/XF Application Programming Manual

Normal Response Mode (NRM) Protocols
EnvoyACP/XF Application Programming Manual–132179
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Link Establishment with IBM SDLC Loop Controller
Link Establishment with IBM SDLC Loop Controller
You also can configure EnvoyACP/XF for an alternate method (OPTION2) of link
establishment procedure, which establishes a link to a remote station through an IBM
SDLC Loop controller. In this configuration, the primary EnvoyACP/XF station sends a
SNRM to the Loop controller. Upon receiving the SNRM, the Loop controller responds
to the primary station with a DM, then attempts to contact the station to which the
SNRM was directed.
The IBM Loop controller expects the primary station to reissue the SNRM. In a
non-error condition, the Loop controller contacts the selected secondary station before
the second SNRM arrives. If contact is established with the secondary station, the Loop
controller responds to the SNRM with a positive response (UA) and the session can be
established.
When configured with SCF for OPTION2 (Figure 3-4
), EnvoyACP/XF ignores the DM
response to the SNRM and the T1TIMER continues to run. When the T1TIMER
expires, EnvoyACP/XF retries the SNRM, and the T1TIMER restarts. Then the SNRM
is retried up to number of retries specified by L2RETRY.
Figure 3-3. Standard NRM Link Establishment
SNRM
ServerNet WAN
Concentrator
SNRM
DM
Tandem NonStop System
Primary/Supervisor
Station
Primary station places
the nonresponding
station(s) in an
error-stop state.
DM
043
Tributary Stations