insys icom GPRS 5.1, Руководство пользователя, Страница: 81 / 102

INSYS GPRS 5.1 serial GSM, GPRS, and EDGE General
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Note: The above mentioned values represent the theoretically maximum possible
values.
In practice, the following applies:
GPRS/EDGE will not provide guaranteed data rates or bandwidths for the applica-
tion. The values allocated by the network provider (coding scheme and time slots
to be used) can change dynamically during a connection and, among other things,
depend on the current amount of connections in the GSM cell.
In the device class B, the INSYS GPRS 5.1 serial supports the GSM services EDGE,
GPRS, CSD and voice. However, only one service can be executed at a time.
8.6 Quality of Service (QoS)
The above mentioned characteristics data rates (in the form of values such as “da-
ta amount per hour” and maximum data amount) and delay times are, among
others, a part of the Quality of Services.
Theoretically, there is a possibility for requesting a certain QoS profile from the
provider during the connection setup via
AT commands ( AT+CGQREQ ) or to define
a minimum profile ( AT+CGQMIN ) which must exceeded by the QoS offered by the
provider, in order to enable the device to establish the connection.
Experience has shown that these settings will not show any success regarding
performance improvement, as the providers always supply "Best Effort” as QoS,
i.e. the best values according to the current network load during the moment of
the connection setup.
8.7 Delay Times
Usually, there will be marginally higher delays than with a "normal" connection
via GSM.
The delays will mostly be below one second.
The average delay times are stated with 700 ms, for GSM values of 500 ms are as-
sumed. In rare cases, delays of several seconds are possible; the applications at
the GPRS end devices should therefore be set to maximum delay times.