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Local
area
network
Server
Router
Local
area
network
Server
Router
Corporate 2
Corporate 1
Intra-PLMN
backbone
network
(IP based)
Serving GPRS
Support Node
(SGSN)
Point-To-
Multipoint
Service
Center
(PTM SC)
Gateway GPRS
Support Node
(GGSN)
GPRS
INFRASTRUCTURE
HLR/AuC
MSC
BSC
BTS
Packet
network
PSTN
Packet
network
SS7
Network
Packet
network
Data
network
(Internet)
Packet
network
Data
network
(X.25)
Packet
network
Inter-PLMN
Backbone
network
Border
Gateway (BG)
Gb
Gr
Gd
Gi.IP
Gi.X.25
Firewall
Firewall
Firewall
Um
R/S
SMS-GMSC
Gr
Gd
Gs
Gs
Gp
Gn
Gn
EIR
MAP-F
Figure 4. GPRS architecture.
GPRS introduces two new network nodes in the GSM PLMN: The Serving GPRS Support
Node (SGSN), which is at the same hierarchical level as the MSC, keeps track of the
individual MSs’ location and performs security functions and access control. The SGSN is
connected to the base station system with Frame Relay. The Gateway GSN (GGSN)
provides interworking with external packet-switched networks, and is connected with SGSNs
via an IP-based GPRS backbone network. The HLR is enhanced with GPRS subscriber
information, and the SMS-GMSCs and SMS-IWMSCs are upgraded to support SMS
transmission via the SGSN. Optionally, the MSC/VLR can be enhanced for more-efficient co-
ordination of GPRS and non-GPRS services and functionality: for example, paging for circuit-
switched calls that can be performed more efficiently via the SGSN, and combined GPRS
and non-GPRS location updates.
The GPRS air interface uses the basic features of the GSM air interface, such as spectrum
division, modulation and burst structure. Thus both the circuit switched GSM services and
the GPRS service can be provided using the same carrier. However, the GPRS backbone
network has been designed so that it is not dependent on the air interface used. Thus it will
be possible to reuse the GPRS backbone network with different air interfaces. This implies
that GPRS is an important step in providing packet data services in the next generation
wireless systems
The Nokia D211 supports multi slot
class 6
(Max Rx time slots 3, Max Tx time slots 2, sum
4, type 1). Type 1 MS are not required to transmit and receive at the same time. No time
slots are allocated explicitly for one user for a GPRS call period. Time slots are allocated only
when needed. Allocation can be changed dynamically based on traffic conditions: for
example, voice time slots are added when new voice calls are made or more time slots are
given for GPRS when off-peak for voice. One time slot can be from 9.05 kbit/s to 21.4 kbit/s
depending on coding scheme. The Nokia D211 supports all four channel coding schemes
GPRS-1, GPRS-2, GPRS-3 and GPRS-4.
Networks support initially schemes GPRS-1 and
