At Commands Not Applicable In Mux Mode; Air Interface Limitation; Application Data Recovery - Wavecom GX64 GSM 27.010 Multiplexer Feature Application Note

Some local settings may cause "global" activities and should only be set in one
channel. For instance ATS0 and AT+CGAUTO should not be used in more than one
channel.
6.2

AT Commands Not Applicable in MUX Mode

Some AT commands are not applicable in MUX mode. One such an example is
AT+CMUX command – AT+CMUX set command returns ERROR in MUX mode. Another
example is AT+IPR command – this command may be issued in MUX mode but it will
have no effect on the channel's operation. One can find whether or not a command
works with MUX in the AT commands' characteristic table under "Works with MUX".
6.3

Air Interface Limitation

Although 27.010 MUX provides capability to multiplex on the serial link, the air link is
not multiplexed; all the limitations of air link still apply in MUX mode. GR/GS64
wireless CPU is a mobile class B device; as a result, simultaneous GPRS data and
circuit-switched transactions (such as voice calls) are not possible.
For GR/GS64, GPRS will temporarily suspend to support circuit-switched activities
such as CS SMS, Location Updates and voice calls. After the circuit-switched
transactions finish, GPRS is resumed. In serial mode, in order to perform any MO CS
transactions a host application has to explicitly suspend or escape out of a GPRS data
session. But in the MUX mode, both MO and MT CS activities can happen while the
GPRS session is ongoing, which in turn makes the air link limitation an important
design consideration in the MUX mode.
6.4

Application Data Recovery

As discussed in section 6.3, GPRS can be suspended due to the nature of mobile class
B. A host application needs to have an application level mechanism to handle the
possibility of temporary data loss - either through a reliable transport protocol such
as TCP or other application layer re-transmission mechanisms.
Measures can also be taken to reduce the occurrence of GPRS suspension during
heavy GPRS data traffic. This can be managed by scheduling MO Circuit Switched
activities properly. Since MO CS SMS messages are more widely supported by carriers
than Packet Switched (GPRS) SMS messages, the default AT+CGSMS setting of 3 (i.e.
Circuit Switched preferred SMS) is used for simultaneous GPRS and MO SMS. In this
case scheduling would be beneficial.
On the other hand, a basic mode 27.010 does not guarantee reliable transmission of
user data through virtual channels. In basic mode only UIH frames are used to carry
user data and by definition, only headers are checked against FCS. Moreover, basic
mode 27.010 tends to have long recovery time if frames become out-of-sync.
Gx64 APPLICATION NOTE
27.010 MUX Feature
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