General Packet Radio Service
(GPRS)
Adapted from a presentation by
Miao Lu
(mlu@site.uottawa.ca)
Nancy Samaan
(nsamaan@site.uottawa.ca)
SITE, Ottawa University
1
Introduction
 GPRS (General Packet Radio Service)
• Reuse the existing GSM infrastructure
• Introduce packet-switched routing functionality
• Better data transfer rates
• Low cost and connectivity-oriented
• Migration Path to 3G Networks
2
Packet-switched technique
vs. circuit-switched
 In circuit-switching, resources (e.g. a channel) are
allocated to user for duration of connection
•
•
•
Inefficient use of resources
User pays for the whole connection
High QoS: channel maintains real-time connection
 In packet-switching, resources are allocated to user
only for the time it takes to send each packet
•
•
•
A channel can serve many users
User pays by the packet
Ideal for bursty data connections
3
Comparison
 Packet-switched
•
•
•
•
•
High bit rates (up to
170kbit/s)
Shared bandwidth
Variable access times
Friendly bill (based on
volume)
Robust application
support
• Frequent transmission
of small volumes
• Infrequent transmission
of small or medium
volumes
 Circuit-switched
•
•
•
•
•
Low bit rates
(14.4kbit/s)
Reserved bandwidth
Fixed access time
Unfriendly bill (based
on duration)
Limited application
support
• Large volumes
4
GPRS Architecture
5
GPRS Architecture - Components
 New components introduced for GPRS
services:
• SGSN (Serving GPRS Support Node)
• GGSN (Gateway GPRS Support Node)
• IP-based backbone network
 Old components in GSM upgraded for GPRS
services:
• HLR
• MSC/VLR
• Mobile Station
6
GPRS Architecture
SGSN – Serving GPRS Support Node
 At the same hierarchical level as the MSC.
 Transfers data packets between mobile
stations and GGSNs.
 Keeps track of the individual MSs’ location
and performs security functions and access
control.
 Detects and registers new GPRS mobile
stations located in its service area
 Participates into routing, as well as mobility
management functions.
7
GPRS Architecture
GGSN – Gateway GPRS Support Node
 Provides inter-working between PLMN and external
packet-switched networks.
 Converts the GPRS packets from SGSN into the
appropriate packet data protocol format (e.g., IP or
X.25) and sends out on the corresponding packet
data network.
 Participates into the mobility management.
 Maintains the location information of the mobile
stations that are using the data protocols provided by
that GGSN.
 Collects charging information for billing purpose.
8
GPRS Architecture
Backbone Network
 Tunnels of data and signaling messages
between GPRS support nodes.
 Protocol architecture based on the Internet
Protocol (IP).
 GTP (GPRS Tunneling Protocol) used to
tunnel user data and signaling between
GPRS Support Nodes. All PDP (Packet Data
Protocol) PDUs (Protocol Data Units) shall be
encapsulated by GTP.
9
GPRS Architecture
Backbone Network (cont.)
 Two kinds of GPRS backbone Network:
•
•
Intra-PLMN backbone network: The IP network
interconnecting GSNs within the same PLMN.
Inter-PLMN backbone network: The IP network
interconnecting GSNs and intra-PLMN backbone
networks in different PLMNs.
 Two intra-PLMN backbone networks are connected
via the Gp interface using Border Gateways and an
inter-PLMN backbone network.
 Border Gateway handles the packet transfer between
GPRS PLMNs.
10
GPRS Architecture
Backbone Network
Packet Data Network
Inter-PLMN Backbone
Gi
GGSN
BG
Intra-PLMN Backbone
SGSN
Gi
Gp
SGSN
BG
GGSN
Intra-PLMN Backbone
SGSN
11
GPRS Architecture
HLR
 Enhanced with GPRS subscription data and
routing information.
 Accessible from the SGSN via the Gr
interface and from the GGSN via the Gc
interface.
12
GPRS Architecture
MSC/VLR
 Not needed for routing of GPRS data.
 Needed for the co-operation between GPRS
and the other GSM services. e.g.,
• Paging for circuit-switched calls that can be
•
performed more efficiently via the SGSN
Combining GPRS and non-GPRS location
updates
 Receives location information from SGSN or
sends paging requests to SGSN via the Gs
interface.
13
GPRS Architecture
Mobile Station
 GPRS MS includes two components:
• MT (Mobile Terminal). Typically a handset
•
used to access the radio interface.
TE (Terminal Equipment). Typically a laptop or
a Personal Digital Assistant (PDA).
 Could be one unit combing the functionalities
of a MT and a TE.
14
GPRS Architecture
Mobile Station (cont.)
 Three types of MS:
• Class-A: Could be attached to both GPRS and
•
•
other GSM services, and the MS supports
simultaneous operation of GPRS and other
GSM services.
Class-B: Could be attached to both GPRS and
other GSM services, but the MS can only
operate one set of services at a time.
Class-C: Could be exclusively attached to one
service type at a given time.
15
GPRS Architecture
Interfaces
MSC/VLR
HLR
D
Gr
Gs
Gc
A
Gb
TE
MT
R
BSS
Um
Gn
Gn
SGSN
Gi
PDN
GGSN
Ga
Ga
Gp
CGF
SGSN
GGSN
Other PLMN
TE
Gf
Billing
System
EIR
• CGF(Charging Gateway)
16
Packet transfer
Intra-PLMN backbone
PLMN
17
Packet Transfer
 A laptop connects with a GPRS-capable
handset.
 The handset communicates with GSM base
station.
 Base station sends the GPRS packets to
SGSN.
 SGSN encapsulates packets
 Handset location information is updated in
other GSM components, such as HLR.
 SGSN sends encaps. packets to GGSN.
 GGSN decapsulates and sends to PDNs.
18
Communication betw. GPRS station
and IP host
Go red
Return blue
BSC
BTS
BSC
BTS
SGSN
SGSN
MS
Intra-PLMN
GPRS Backbone
PLMN1
Inter-PLMN
GPRS Backbone
Gn
Gp
Border
Gateway
Gn
Intra-PLMN
GPRS Backbone
PLMN2
Border Gateway
Gn
GGSN
SGSN
GGSN
Gi
Packet Data Network(PDN)
Eg.Internet,Intranet
Host
19
Brasche and Walke (adapted)
Router
Routing example
 MS located in PLMN1 sends IP packet to host (e.g.
Web server)
•
•
•
SGSN where sender MS is registered encapsulates IP
packets
Routes them through intra-PLMN backbone to
appropriate GGSN
GGSN decapsulates packets and sends them to IP
network, that forwards to appropriate host
 host sends return packet to home PLMN2 of MS
•
•
•
PLMN2’s GGSN queries HLR and finds that MS is in
PLMN1
Packet is encapsulated and sent to SGSN in PLMN1
SGSN decapsulates packet and delivers to MS
• Note usefulness of inter-PLMN backbone so GPRS
routing does not need to go through PDN
• No encapsulation-decapsulation needed to traverse
backbone
20