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T300/T302
White Paper, August 2002
21
Using GPRS in the T300/T302
Instead of occupying an entire voice channel for
the duration of a data session, the T300/T302
sends/receives data in small packets, as needed,
much like IP on the Internet. Because of this, the
T300/T302 maintains a constant online
connection, its data transmission abilities
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. The T300/T302
works with all four coding schemes, but data
speed will naturally vary according to network
configuration. At the moment, CS-3 and CS-4 are
not supported in any live network, i e present
speed is limited to 40,200 bps.
The GSM system limits the ability to use all eight
time slots, so the T300/T302 uses up to three
time slots for receiving data, and one slot for
transmitting. This means the speed for receiving
data is up to 64,200 bps and up to 21,400 bps for
sending data.
Information about the identity of the phone and
the characteristics of the connection are
described in the PDP (Packet Data Protocol)
context. This information is stored both in the
phone and in the mobile network, so that each
phone is identified and “visible” to the system.
GSM
9,600/14,400
9,600/14,400
9,050/13,400/
15,600/21,400
1
14,400, 19,200 or 28,800 bps (HSCSD)
GPRS
9,050, 13,400,
15,600, 18,100,
21,400, 26,800,
27,150, 31,200
40,200, 42,800,
46,800 or 64,200 bps
2
9,600/14,400
9,600 bps
9,050/13,400/
15,600/21,400
9,050/13,400/
15,600/21,400
9,050/13,400/
15,600/21,400
Figure 4 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 T300/T302 sup-
ports a more efficient coding scheme, giving data
speeds of up to 14,400 bps (with necessary net-
work support). Furthermore, High Speed Circuit
Switched Data (HSCSD) adds the possibility of
using two time slots for receiving data, increasing
the data speed to as much as 28,800 bps (net-
work dependent).
2. In GPRS, data is sent in packets, with up to
three time slots being combined to provide the
necessary bandwidth. The T300/T302 is pre-
pared to support 3+1 time slots, giving speeds of
up to 64,200 bps for receiving data, depending
on coding scheme.