Nokia 30 GSM Connectivity Terminal At Command Manual page 74

If the Nokia 30 does not receive acknowledgement within the required time (network
timeout), the Nokia 30 will send an RP-ERROR to the network. Routing to the TE will be
automatically disabled by setting both <mt> and <ds> values of +CNMI to zero.
PDU mode:
The +CNMA command confirms the reception of a new message (SMS-DELIVER or SMS-
STATUS-REPORT) which is routed directly to the TE. This acknowledgement command
should be used when the +CSMS parameter <service> equals 1. In the PDU mode, it is
possible to send either a positive (RP-ACK) or a negative (RP-ERROR) acknowledgement to
the network. The parameter <n> defines which acknowledgement will be sent. Optionally
(when <length> is greater than zero), an acknowledgement TPDU (SMS-DELIVER-REPORT
for RP-ACK or RP-ERROR) may be sent to the network. The entering of the PDU is carried
out similarly as specified in the command Send Message +CMGS, except that the format of
<ackpdu> is used instead of <pdu> (i.e. SMSC address field is not present). The PDU should
not be written inside double quotes. The TA should not send another +CMT or +CDS result
code to the TE before the previous code has been acknowledged.
If the Nokia 30 does not receive acknowledgement within the required time (network
timeout), the ME should send an RP-ERROR to the network. The Nokia 30 shall
automatically disable routing to the TE by setting both <mt> and <ds> values of the +CNMI to
zero.
The test command returns a list of supported <n> values. If the only value that is supported
is 0, the device does not support the sending of TPDU.
Defined values
<n>:
0
1
2
<length> the length of the actual TP data unit in octets (i.e. the RP layer SMSC address
octets are not counted in the length)
command operates as defined for the text mode
send RP-ACK (or buffered result code received correctly)
send RP-ERROR (if PDU is not given, the Nokia 30 shall send an
SMS-DELIVER-REPORT with a GSM 03.40 TP-FCS value set to
'FF' (unspecified error cause))
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