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General Packet Radio Service General Packet Radio Service (GPRS)(GPRS)

Miao Lu Miao Lu (mlu@site.uottawa.ca)(mlu@site.uottawa.ca)

Nancy Samaan Nancy Samaan (nsamaan@site.uottawa.ca)(nsamaan@site.uottawa.ca)

SITE, Ottawa UniversitySITE, Ottawa University

CSI 5171 (95.533)Network Architectures, Services, Protocols and Standards

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AgendaAgenda

IntroductionIntroduction

Part IPart I

• GPRS Architecture

Part IIPart II Bearer Services and Supplementary

Services Mobility Management GPRS Limitations

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IntroductionIntroduction

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

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Packet-switched techniquePacket-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

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ComparisonComparison

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 ArchitectureGPRS Architecture

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GPRS Architecture - GPRS Architecture - ComponentsComponents

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 ArchitectureGPRS ArchitectureSGSN – Serving GPRS Support NodeSGSN – 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

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GPRS ArchitectureGPRS ArchitectureGGSN – Gateway GPRS Support NodeGGSN – 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 ArchitectureGPRS ArchitectureBackbone NetworkBackbone 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 ArchitectureGPRS ArchitectureBackbone Network Backbone Network (cont.)(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 ArchitectureGPRS ArchitectureBackbone NetworkBackbone Network

Inter-PLMN Backbone

Packet Data Network

Intra-PLMN Backbone Intra-PLMN Backbone

GGSN BG

SGSN SGSN

BG GGSN

SGSN

Gi GiGp

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GPRS ArchitectureGPRS ArchitectureHLRHLR

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 ArchitectureGPRS ArchitectureMSC/VLRMSC/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 ArchitectureGPRS ArchitectureMobile StationMobile 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 ArchitectureGPRS ArchitectureMobile Station Mobile Station (cont.)(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 ArchitectureGPRS ArchitectureInterfacesInterfaces

TE MT BSS SGSN GGSN PDN TE

MSC/VLR HLR

SGSNCGF

EIR

BillingSystem

Other PLMN

GGSN

R Um

AGs

DGr

Gc

Gb Gn Gi

Gn Gp

Gf

GaGa

• CGF(Charging Gateway)

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Packet transfer Packet transfer

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Packet TransferPacket 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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AgendaAgenda

IntroductionIntroduction

Part IPart I

• GPRS Architecture

Part IIPart II Bearer and Supplementary Services Mobility Management GPRS Limitations

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Bearer and Supplementary Services of GPRSBearer and Supplementary Services of GPRS

The bearer servicesbearer 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 ServicesSupplementary 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 GPRS Bearer Services PTP servicesPTP services

Two types :Connection-Oriented Network Service (PTP-CONS) :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) :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 GPRS Bearer Services PTM ServicesPTM Services

enables the transmission of a single message to multiple destinations. Multicast service (PTM-M): 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): 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 ):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

• Mobility management is the means by which GPRS keeps track of a mobile subscriber location while connected to the Network.

• Main concepts :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 Mobility Management IdentifiersIdentifiers

International Mobile station Equipment Identity (IMEI) : (IMEI) : Specified for each equipment by the manufacturer

International Mobile Subscriber Identity (IMSI):(IMSI):

• It is stored in the subscriber identity module (SIM). Temporary International Mobile Subscriber Identity

(TMSI):(TMSI):

• assigned by the VLR. Packet Temporary Mobile Subscriber Identity (P-TMSI):(P-TMSI):

• (during attachment by the SGSN) . Temporary Link Layer Identifier (TLLI):(TLLI):

• During the attachment phase , a TLLI is randomly generated by mobile.

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Mobility Management Mobility Management GPRS service Areas[8]GPRS service Areas[8]

SA : Service Area

RA: Routing Area

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Explicit Detach

Mobility Management Mobility Management Mobility Management StatesMobility Management States

IDLE

READY

STANDBY

GPRS Attach GPRS Detach

Timer expiry/Force STANDBY/

Abnormal RLC condition

PDU Transmission

/Reception

reachable mobile

unreachable mobile

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IDLE StateIDLE State GPRS MS is unreachable - MS may receive PTM-M message

READY stateREADY 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 StateSTANDBY 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

Mobility Management Mobility Management Mobility Management States Mobility Management States (cont.)(cont.)

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Mobility Management Mobility Management GPRS network accessGPRS network access

• An MS can connect to the GPRS network by requesting a GPRS attachattach procedure.

• The outcome is the establishment of a logical link between the MS and a single SGSN and the creation of a mobility mobility management contextmanagement context.

• The logical link is uniquely defined by the identifier TLLI 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 Mobility Management AttachmentAttachment

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 Mobility Management AttachmentAttachment

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 -Mobility Management -Attachment [5]Attachment [5]

1.Attach RequestMS BSS New SGSN Old SGSN GGSN EIR

NewMSC/VLR

HLR oldMSC/VLR

2. Identification Request

3. Identification Response3. Identity Request

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

8. Attach Accept

9. Attach Complete 10. TMSI Reallocation complete

7c. CancelLocation7d.ACK

7a. Location Update Request7b. Update Location

7e. Insert Subscriber data

7h. Location Update Accept

7f. Insert Subscriber data ACK7b. Update Location ACK

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Mobility Management –Mobility Management –Location managementLocation management

Three types of location management procedures:

• Cell Update: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 :Intra-SGSN routing update :

• MS changes RA and remains in the same SGSN(STANDBY &READY states).

•Inter-SGSN routing update: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 Mobility Management Packet Data Protocol Packet Data Protocol((PDP) SessionPDP) 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 Mobility Management Packet Data Protocol Packet Data Protocol((PDP) SessionPDP) 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 Mobility Management Packet Data Protocol Packet Data Protocol((PDP) ContentPDP) 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 Mobility Management Packet Data Protocol Packet Data Protocol((PDP) Session[8]PDP) Session[8]

An MS with two PDP contexts Active

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Mobility Management Mobility Management PDP context Activation [5]PDP context Activation [5]

MS SGSN GGSN

Activate PDP Context Request

MS Activate PDP Context Accept

Create PDP Context Request

Create PDP Context Response

PDP type,PDP AddressQoS Requested,Access Point,…

PDP type,PDP Address, IMSI,QoS Negotiated,Access Point,…

PDP type,QoS Negotiated,…PDP type,PDP AddressQoS Negotiated,…

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Mobility Management Mobility Management PDP context Deactivation [5]PDP context Deactivation [5]

MS SGSN GGSN

MS DEACTIVATE PDPCONTEXT REQUEST(NSAPI)

GTP DELETE PDP CONTEXTREQUEST (NSAPI,IMSI)

GTP DELETE PDP CONTEXTRESPONSESM DEACTIVATE PDP

CONTEXT ACCEPT(NSAPI)

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Mobility ManagementMobility ManagementDetachmentDetachment

Two types of Detachments :

MS initiated Detachment:

Network Initiated Detachment:

(Ex : service Termination, Network congestion)

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Mobility ManagementMobility Management MS Initiated Detachment [5]MS Initiated Detachment [5]

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Mobility Management Network Initiated Detachment Network Initiated Detachment [5][5]

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Routing ExampleRouting Example

PLMN1 PLMN2

MS

BTS

BSC

SGSNGn

Intra-PLMNGPRS Backbone

Gn

Gn

SGSN

GGSNGi

Packet Data Network(PDN)Eg.Internet,Intranet

Border Gateway

Gp

Inter-PLMNGPRS Backbone

Border Gateway

Intra-PLMNGPRS Backbone

GGSN

RouterLANHost

SGSN

BSCBTS

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GPRS LimitationsGPRS 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)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)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.