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Um
R/S
Serving GPRS
Support Node
(SGSN)
Border
Gateway (BG)
Packet
Inter-PLMN
network
Backbone
network
Gp
Firewall
Point-To-
Multipoint
Service
Center
(PTM SC)
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
BTS
BSC
MSC
Gb
Gr
Gd
Gs
Gn
GPRS
INFRASTRUCTURE
Intra-PLMN
backbone
network
Gateway GPRS
(IP based)
Support Node
(GGSN)
Gn
Data
Firewall
network
(X.25)
Packet
network
PSTN
HLR/AuC
Gs
Gr
Packet
SS7
network
Network
EIR
MAP-F
Router
Firewall
Data
Packet
network
network
(Internet)
Gi.IP
Gi.X.25
Packet
network
Router
SMS-GMSC
Gd
Corporate 1
Server
Local
area
network
Corporate 2
Server
Local
area
network
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