Transcript General Packet Radio Service (GPRS) Miao Lu (2705914) Nancy

CSI 5171 (95.533)
Network Architectures, Services, Protocols and Standards
General Packet Radio Service
(GPRS)
Miao Lu
([email protected])
Nancy Samaan
([email protected])
SITE, Ottawa University
1
Agenda
 Introduction
 Part I
• GPRS Architecture
 Part II
 Bearer Services and Supplementary
Services
 Mobility Management
 GPRS Limitations
2
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
3
Packet-switched technique
 Share radio resources: users share a pool of
channels
• Channels are allocated to users only when
•
packets are to be sent or received
Users can use several time slots (packet data
channels) simultaneously
 Volume-charging: charging is based on traffic
volume instead of the duration of a session
4
Comparison
 Packet-switched
•
•
•
•
High bit rates (up to
170kbit/s)
Short 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
(maximum 14.4kbit/s)
Long access times
Unfriendly bill (based
on duration)
Limited application
support
• Large volumes
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GPRS Architecture
6
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
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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.
 Participates into routing, as well as mobility
management functions.
 Detects and registers new GPRS mobile
stations located in its service area
8
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.
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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.
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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.
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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
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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.
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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.
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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.
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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.
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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)
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Packet transfer
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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.
 GPRS packets routing information and
handset location information are updated in
other GSM components, such as HLR.
 SGSN communicates with GGSN.
 GGSN sends the packets to PDNs.
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Agenda
 Introduction
 Part I
• GPRS Architecture
 Part II
 Bearer and Supplementary Services
 Mobility Management
 GPRS Limitations
20
Bearer and Supplementary Services of GPRS
 The bearer services of GPRS offer end-to-end packet
switched data transfer.
 Two different kinds of bearer services :
•
•
PTP (Point-to-point) services
PTM (Point-to-multipoint) services
• Supplementary Services : SMS call, call forwarding
unconditional (CFU), call forwarding on mobile
subscriber not reachable (CFNRc), and closed user
group (CUG) .
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GPRS Bearer Services
PTP services
Two types :
Connection-Oriented Network Service (PTP-CONS) :
• A logical relation is established between users.
• supports bursty transactional or interactive APs based on X.25.
• Multiple packets are sent between a single source and destination.
• Examples : Credit card validations, Telnet, and Database access.
ConnectionLess Network Service (PTP-CLNS) :
• A datagram type service based on the connectionless network protocol
(ex: IP).
• Supports bursty non-interactive applications.
• No logical link required between users.
• Each packet is sent is independent of other packets.
• Examples :Electronic mail, Internet ‘s World Wide Web.
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GPRS Bearer Services
PTM Services
enables the transmission of a single message to multiple destinations.
 Multicast service (PTM-M):
• Addressed to all subscribers in a geographical area group identifier
indicating whether to all subscribers or to a specific PTM group
• Example : News, Weather and Traffic reports.
 Group call service (PTM-G):
• Only a predefined group of subscribers controlled by a multicast
server will receive the message transmitted.
• Group members must join the PTM-G call.
• Real time delivery.
• Example: Conferencing services.
 IP Multicast (IP-M ):
• Messages are transmitted to a specific group.
• Group members must join the IP-M call.
• Real time delivery.
• Examples : Live multimedia transmissions.
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Mobility Management
• Mobility management is the means by which GPRS keeps track of a
mobile subscriber location while connected to the Network.
• Main concepts :
• GPRS Identifiers.
• GPRS service areas.
•GPRS mobility management states
•
GPRS network access.
• Attachment.
• Location management
• Packet Data protocol PDP context
• Detachment
•
Routing Example
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Mobility Management
Identifiers
 International Mobile station Equipment Identity (IMEI) :
Specified for each equipment by the manufacturer
 International Mobile Subscriber Identity (IMSI):
•
It is stored in the subscriber identity module (SIM).
 Temporary International Mobile Subscriber Identity
(TMSI):
•
assigned by the VLR.
 Packet Temporary Mobile Subscriber Identity (P-TMSI):
•
(during attachment by the SGSN) .
 Temporary Link Layer Identifier (TLLI):
•
During the attachment phase , a TLLI is randomly
generated by mobile.
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Mobility Management
GPRS service Areas[8]
SA : Service Area
RA: Routing Area
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Mobility Management
Mobility Management States
IDLE
unreachable mobile
Explicit Detach
GPRS Detach
READY
reachable mobile
PDU
Transmission
/Reception
STANDBY
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Mobility Management
Mobility Management States (cont.)
IDLE State
 GPRS MS is unreachable - MS may receive PTM-M message
READY state
 MS can send and receive PDP PDU, and receive PTM-P and PTM-G
data. MS informs SGSN when it changes cells.
 A timer monitors the ready state and upon its expiry, the MS is put on
standby.
STANDBY State
 MS
is attached to GPRS MM. - MS and SGSN have established MM
contexts. MS can receive PTM-M and PTM-G data (i.e. can receive
paging message)
 MS execute MM procedure to inform SGSN when MS enter a new RA
 PTP data reception and transmission, and PTM-G data transmission
are not possible
 MS does not inform SGSN when a change of cell in the same RA
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Mobility Management
GPRS network access
• An MS can connect to the GPRS network by requesting a
GPRS attach procedure.
• The outcome is the establishment of a logical link between
the MS and a single SGSN and the creation of a mobility
management context.
• The logical link is uniquely defined by the identifier TLLI
and is used subsequently in messages exchanged between
the MS and SGSN.
• This identifier is changed when the MS is served by a new
SGSN.
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Mobility Management
Attachment
Before a mobile station can use GPRS services, it must
register with an SGSN of the GPRS network. The network
checks if the user is authorized, copies the user profile
from the HLR to the SGSN, and assigns a packet
temporary mobile subscriber identity (P-TMSI) to the user.
Steps :
• Inform the network for the MS’s request to be active
• Network checks the Ms’s identity
• Download MS’s subscription information from HLR to
SGSN.
• Update MSC/HLR
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Mobility Management
Attachment
GPRS Attach function :
•Authenticate the mobile
•Generate the ciphering key
•Enable the ciphering
•Allocate temporary identity (TLLI)
•Copy subscriber profile from HLR to SGSN
After GPRS attach
•The location of the mobile is tracked
•Communication between MS and SGSN is secured
•Charging information is collected
•SGSN knows what the subscriber is allowed to do
•HLR knows the location of the MS in accuracy of SGSN
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Mobility Management -Attachment [5]
MS
BSS
New SGSN Old SGSN
1.Attach Request
3. Identity Request
GGSN
EIR
New
old
HLR
MSC/VLR
MSC/VLR
2. Identification Request
3. Identification Response
3. Identity Response
4. Authentication
5. IMEI check
6a. Update Location
6b. Cancel Location
6c. Cancel Location ACK
6d. Insert Subscriber Data
6d. Insert Subscriber Data ACK
6e. Update Location ACK
7a. Location Update Request
8. Attach Accept
7h. Location Update Accept
9. Attach Complete 10. TMSI Reallocation complete
7b. Update Location
7c.
Cancel
Location
7d.ACK
7e. Insert Subscriber data
7f. Insert Subscriber data ACK
7b. Update Location ACK
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Mobility Management –
Location management
Three types of location management procedures:
• Cell Update:
• MS informs the network of its current cell location( in READY state).
• MS listens periodically to special control channel for cell identity.
•Intra-SGSN routing update :
• MS changes RA and remains in the same SGSN(STANDBY
&READY states).
•Inter-SGSN routing update:
• When the entry of MS to a new RA triggers a change of
SGSN service area(STANDBY &READY states).
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Mobility Management
Packet Data Protocol(PDP) Session
• An MS can request to activate one or more PDP (Packet Data
Protocol) contexts which specify the PDNs (Packet Data Networks) it
want to access.
• A PDP context activation procedure is initiated for each required
PDP session.
• Triggered by the MS or a request from a PDN.
• Contains the parameters required to transfer packets between the
MS and the PDN via a GGSN.
• An MS can have more than one PDP context.
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Mobility Management
Packet Data Protocol(PDP) Session
• An MS specifies its network service access point and the Access
Point Name (APN) of the PDN it wants to connect to.
• The SGSN identifies the corresponding GGSN and make its aware of
the MS.
• A two way point-to-point path (tunnel) is uniquely identified by a
tunnel ID (TID ) and is established between the SGSN and the GGSN.
• At the MS a PDP context is identified by a Network Service Access
Point Identifier(NSPAI), used by the MS for data transfers.
• Ms can be assigned static or dynamic addresses
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Mobility Management
Packet Data Protocol(PDP) Content
• A PDP (PACKET Data Protocol) contains:
• The type of network PDP used (X25, IP...).
• PDP Addresses of the terminal (x.121, IP).
• IP Addresses of the SGSN where the subscriber is localized.
• The access point to the service network used (NSAPI).
• The quality of service.
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Mobility Management
Packet Data Protocol(PDP) Session[8]
An MS with two PDP contexts Active
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Mobility Management
PDP context Activation [5]
MS
SGSN
GGSN
Activate PDP Context Request
PDP type,PDP Address
QoS Requested,Access Point,…
Create PDP Context Request
PDP type,PDP Address, IMSI,
QoS Negotiated,Access Point,…
MS Activate PDP Context Accept
PDP type,PDP Address
QoS Negotiated,…
Create PDP Context Response
PDP type,QoS Negotiated,…
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Mobility Management
PDP context Deactivation [5]
MS
SGSN
GGSN
MS DEACTIVATE PDP
CONTEXT REQUEST(NSAPI)
GTP DELETE PDP CONTEXT
REQUEST (NSAPI,IMSI)
SM DEACTIVATE PDP
CONTEXT ACCEPT(NSAPI)
GTP DELETE PDP CONTEXT
RESPONSE
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Mobility Management
Detachment
Two types of Detachments :
 MS initiated Detachment:
 Network Initiated Detachment:
(Ex : service Termination, Network congestion)
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Mobility Management
MS Initiated Detachment [5]
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Mobility Management
Network Initiated Detachment [5]
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Routing Example
BSC
BTS
BSC
BTS
SGSN
SGSN
MS
PLMN1
Intra-PLMN
GPRS Backbone
Inter-PLMN
GPRS Backbone
Gn
Border
Gateway
Gn
Intra-PLMN
GPRS Backbone
Gp
PLMN2
Border Gateway
Gn
GGSN
SGSN
GGSN
Gi
Packet Data Network(PDN)
Eg.Internet,Intranet
Router LAN Host
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GPRS Limitations
•
Speeds Much Lower in Reality
•
Support of GPRS Mobile Terminate by Terminals is Not Ensured
•
Packet switching means that data packets can traverse different
routes and then be reassembled in their final destination leading
to potential transit delays affecting the Quality of Service.
•
Operators may decide to charge based on time rather than volume,
which may destroy the cost advantage that GPRS provides today.
•
Requires major network modifications: Many network elements to be
upgraded and totally new to be introduced
•
Expensive: Not much time for invest to be returned due to upcoming 3rd
generation technology
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References (papers)
[1] Dale R. Shelton, “General Packet Radio Service”, Aether Systems,
Incorporated, 2001
[2] Agilent Technologies, “Understanding General Packet Radio Service
(GPRS)”, Technical report, 2001.
[3] Christian Bettstetter, Hans-J¨org V¨ogel and J¨org Ebersp¨acher, “GSM
Phase 2+ General Packet Radio Service GPRS: Architecture, Protocols,
and Air Interface”, IEEE Communication Surveys, vol. 2, n. 3, 1999.
[4] ETSI, “GSM 02.60 Digital cellular telecommunications system (Phase2+):
General Packet Radio Service, Service Description Stage 1”.
[5] ETSI, “GSM 03.60 Digital cellular telecommunications system (Phase2+);
General Packet Radio Service, Service Description Stage 2”, 1998.
[6] L. Logrippo D. Amyot, N.Hart and P. Forhan, “Formal Specification and
Validation using a Scenario-Based Approach: The GPRS Group-Call
Example”,ObjecTime Workshop on Research in OO Real-Time
Modeling, Ottawa, Canada, pp. 99–118, Jan. 1998
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References (papers)
[7] B. Ghribi L. Andriantsiferana and L. Logrippo, “Prototyping and Formal
Requirement Validation of GPRS: A Mobile Data Packet Radio Service
for GSM”, Proceedings of 7th Int. Working Confrence on Dependable
Computing For Critical Applications (DCCA-7), san Jose,
California,USA, pp. 99–118, Jan. 1999.
[8] B. Ghribiand L. Logrippo, “Understanding GPRS: The GSM Packet Radio
Service”, Computer Networks, vol. 34, pp. 763–779, 2000.
[9] Herman Rao Yi-Bing Lin and Imrich Chlamtac, “General Packet Radio
Service (GPRS): Architecture, Interfaces, and Deployment”, Journal of
Wireless Communiations and Mobile Computing, vol. 1, n. 1, pp. 77–92,
2001.
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