Page 87 - From GMS to LTE

General Packet Radio Service (GPRS) and EDGE 73

Data packets of user 1 with a
different destination address

Data packets of user 2

Router Router

Data packets of different users are
Data packet
of user 1 transferred one after another

Figure 2.2 Packet‐switched data transmission.

To send packet‐switched data over existing GSM networks, GPRS was designed as a
packet‐switched addition to the circuit‐switched GSM network. It should be noted that
IP packets can be sent over a circuit‐switched GSM data connection as well. However,
until they reach the Internet service provider they are transmitted in a circuit‐switched
channel and thus cannot take advantage of the benefits described below. GPRS, on the
other hand, is an end‐to‐end packet‐switched network and IP packets are sent packet
switched from end‐to‐end.
The packet‐switched nature of GPRS also offers a number of other advantages for
bursty applications over GSM circuit‐switched data transmission:

By flexibly allocating bandwidth on the air interface, GPRS exceeds the slow datarates
●
of GSM circuit‐switched connections of 9.6 or 14.4 kbit/s. Datarates of up to 170
kbit/s are theoretically possible. Multislot class 10 mobile devices (see below) reach
speeds of about 85 kbit/s and are thus in the range of the fixed‐line analog modems
that were in widespread use at the time GPRS was introduced.
With the EDGE update of the GSM system, further speed improvements were made.
●
The enhancements of EDGE for GPRS are called EGPRS in the standards. The term,
however, is not widely used in practice and preference has been given to the term
EDGE. With an EDGE class 32 mobile device, it is possible to reach transmission
speeds of up to 270 kbit/s.
GPRS is usually charged by volume and not by time, as shown in Figure 2.3. For subscribers
●
this offers the advantage that they pay for downloading a web page but not for the
time spent reading it, as would be the case with a circuit‐switched connection. For
the operator of a wireless network it offers the advantage that the scarce resources on the
air interface are not wasted by ‘idle’ data calls because they can be used for other
subscribers.
GPRS significantly reduces call set‐up time. Similar to a fixed‐line analog modem, a
●
GSM circuit‐switched data call took about 20 seconds to establish a connection with
the Internet service provider, while GPRS accomplishes the same in less than 5
seconds.