General Packet Radio Service (GPRS) is a GSM Phase 2+
bearer service. It represents the first true advance in packet
data service since CDPD and is the first packet data service on
wireless digital networks. It is currently being launched in
Europe on the GSM networks, but a common start-up problem
has hampered its growth—lack of equipment! GPRS handsets
are still in short supply. This is a recurring nightmare for operators
of all new technologies: When WAP was introduced,
there was a lack of handsets and content.
This results from the classic “chicken-and-egg” syndrome.
Because GPRS handsets cost more to make in small quantities,
prices to consumers are higher. With low sales figures, manufacturers
produce small quantities of product. The ramp-up to
higher production volumes will take time, but it will happen, of
that you can be sure. GPRS will be the backbone of GSM and
TDMA networks for wireless packet data communications.
Radio resources are shared by all mobile stations, and GPRS
parses out those resources as needed to each user because
Internet browsing usually results in data communication that
is transmitted in bursts rather than steady streams. This creates
greater efficiency in network capacity management: Data
rates as high as 115 Kbps can be achieved.
Unlike SMS messaging, GPRS was not originally a part of
the GSM (or TDMA) network. For this reason, some new network
elements must be introduced to the GSM architecture,
and some mobility management functions must be modified as
shown in Figure 2-5. Unlike CDPD, however, GPRS provides
a data overlay within the standard GSM infrastructure by adding these additional elements. Packet data through a GPRS
network does not use any circuit-switched network resources.
One of these additional network elements is called the
Gateway GPRS Support Node (GGSN). Essentially, this is a
packet router with some mobility management functions. It
connects to the GSM network and the external packet node
network through standard interfaces.
The second new element is very similar in function except
that it connects directly to the Base Station Controller (BSC).
The Serving GPRS Support Node (SGSN) is responsible for
handling packet data to and from the mobile unit.
BT Cellnet began offering GPRS network access to mobile
phone users in Europe in 2001. Recent tests of those services,
however, have not impressed many customers. Actual data
rates have not matched expectations, but it is a new service and
there will be a great deal of “fine tuning” to the system over the
next few months.
When GPRS fulfills its promise of higher data rates, many
new applications will be possible over GSM and TDMA networks.
GPRS will fully enable mobile Internet applications
similar to Web browsing on a desktop computer. Applications
will include file transfer, Web surfing, and of course, email
with attachments.
As with any new technology, GPRS does have some negative
impact on a network. Not only are data resources shared, they are shared with voice resources—for any given cell site, channels
must be divided between voice users and GPRS users. If all
voice channels are in use and file transfers are taking place on
all packet-data channels, there is no more capacity for that particular
cell site until someone stops using some of the resources.
Dynamic allocation of resources can only do so much. 70