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Figure 6. A comparison between GSM and GPRS.
1. A normal GSM call uses only one of eight repeating time slots in the GSM channel, giving a data speed of
9,600 bps. The T290i/T290c supports a more efficient coding scheme, giving data speeds of up to 14,400 bps
(with necessary network support). Furthermore, High Speed Circuit Switched Data (HSCSD) adds the possibil-
ity of using two time slots for receiving data, increasing the data speed to as much as 28,800 bps (network
dependent).
2. In GPRS, data is sent in packets, with up to three time slots being combined to provide the necessary band-
width. The T290i/T290c is prepared to support 3+1 time slots (three slots for receiving data and one slot for
transmitting data), giving speeds of up to 64,200 bps for receiving data, depending on coding scheme.
Using GPRS in the T290i/T290c
Instead of occupying an entire voice channel for
the duration of a data session, the T290i/T290c
sends/receives data in small packets, as needed,
much like IP on the Internet. Because of this, the
T290i/T290c maintains a constant online connec-
tion. Its data transmission abilities are summoned
by the application in use on an as-needed basis.
The GPRS specification includes four coding
schemes – CS1, CS2, CS3 and CS4 – that allow
data speeds of 9,050 bps, 13,400 bps, 15,600 bps
and 21,400 bps respectively using one time slot.
The T290i/T290c works with all four coding
schemes, but data speed will naturally vary accord-
ing to network configuration. At the moment, CS3
and CS4 are not supported in any live network, i.e.,
present speed is limited to 40,200 bps using three
time slots.
The GSM system limits the ability to use all eight
time slots, so the T290i/T290c uses up to three
time slots for receiving data, and one slot for trans-
mitting (3+1). This means that for CS4, the speed
for receiving data is up to 64,200 bps and up to
21,400 bps for sending data.
25
White Paper
T290i/T290c
October 2004
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