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P800/P802
White Paper, January 2003
100
Here is a summary of the slot usages in HSCSD. One ‘uplink’ and 1 to 2 ‘downlinks’.
Analogue and ISDN (V110) Bearer Service Types
CSD and HSCSD are capable of Analogue and, where supported by the mobile operator, ISDN
connections. ISDN offers faster call set-up time and can increase the performance of an HSCSD
connection due to the limitations in analogue modem technology. The simplest option is to test
ISDN bearer mode, and switch to analogue if no connection can be made. Note that due to
network limitations, analogue is often the only bearer that works when the user is roaming.
GPRS
GPRS mode combines the speed advantages of multi-timeslot working with packet data
efficiency. Instead of utilizing a constant stream of timeslots in a circuit-switched call, GPRS
mode sends/receives data in small packets, as needed, much like IP on the internet. Capacity is
only used when data is being sent or received, which means that it is possible to be “constantly”
connected so that applications have immediate access to networked servers. The radio resources
are shared between users in a much more efficient way than is possible using circuit-switched
methods – timeslots are dynamically allocated to those users who are transmitting and receiving
data. The service is typically charged by the amount of data transferred.
Connection set-up is fast and the P800 will normally be left connected for the whole time it is
switched on. When applications need to transfer large amounts of data such as files, images etc,
it is possible to increase bandwidth by using more timeslots for the duration of the transfer. The
P800 supports up to 4+1 timeslots receive + transmit. The GSM network will dynamically allocate
timeslot resources depending on current network conditions.
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