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GPRS BasicsGPRS Basics
Zhang ChunpingZhang Chunping
AgendaAgenda
GPRS Network Structure
GPRS Interface and Protocol
GPRS Address , Identity
GPRS Radio Interface Technology
GPRS Mobility Management
GPRS Session Management
GPRS Network Structure
GPRS Interface and Protocol
GPRS Address , Identity
GPRS Radio Interface Technology
GPRS Mobility Management
GPRS Session Management
What’s GPRS
GPRS - General Packet Radio Service
High spectrum efficiency for data application
provide data service based on existing GSM
GPRS can keep long connection with network , charge based on data flow
internetLow Speed Circuit Switching Data Service
Low Spectrum efficiency Long Time for Call Setup Narrow Bandwidth & Low Data Rate High Cost
Disadvantages for Circuit Switching Data Service
IWFIWF
Support connecting with PSTN/ISDN/PDN
Provide Data & Fax Service
Most Data rate is just 9600bps
Support transparent & non-transparent Data
Service
Demands increase IWF Function Module in MSC
9.6K
57.6K
171.2K
384K
2M
GSM Revolution
GPRS Network StructureGPRS Network Structure
BTS SGSN GGSNBSC
MSC/VLR
Gi
Gn
GrGs
Gb
Gn
A
Abis
HLR
IPNetwork
GPRSBackbone
BGBG
Other PLMN
Gp
PCU
SGSN
GGSN
Gn
GnBGBG
SS7
GPRS CompositionGPRS Composition
SGSN-Serving GPRS support Node
GGSN-Gateway GPRS Support Node
BG- Border Gateway
PCU- Packet Control Unit
GPRS Mobile Station
Network access control
Authentication
Charging information collection
SGSN FunctionSGSN Function
Routing and tunnel transmission
Encryption and decryption
Subscriber data storage and forwarding
Route selection
Encapsulation and tunnel transmission
MM and SM
Network access control (external PDN side)
Message filtering
Charging information collection
SM
Route selection and forwarding
Storage and forwarding
Route selection
Address translation and mapping
Encapsulation and tunnel transmission
Dynamical IP address allocation( optional)
GGSN FunctionGGSN Function
BG realize the interworking between operators
Based on router
Safety protocol and route protocol Embedded
BG function, GPRS Backbone NetworkBG function, GPRS Backbone Network
GPRS backbone network based on IP protocol
Consist of backbone router
Interworking with each NE, SGSN, GGSN…
Every NE occupy unique IP address
Save GPRS subscription data
Provide location/route information for MM and route selection, such as:
Save and update user SGSN number and address
GPRS user location deletion indicator
MS reachable tag
HLR FunctionHLR Function
HLR GPRS user informationHLR GPRS user information
Domain Description
IMSI User identifier
MSISDN User basic MSISDN
SGSN Number Registered SS7 number of SGSN
SGSN Address Registered SGSN IP addressSMS Parameters 短消息有关的用户签约数据MS Purged for GPRS 用户 GPRS 清除标志MNRG 用户 GPRS不可及标志GGSN-list 列表,每一项包含某一 GGSN的 SS7号码和 IP地址
PDP Context Identifier PDP上下文索引PDP Type PDP类型PDP Address PDP地址
Qos Profile Subscribed 用户登记的 Qos过滤VPLMN Address Allowed 是否允许用户使用 VPLMN的 APNAccess Point Name 外部分组数据网接入点
MSC/VLR Additional FunctionMSC/VLR Additional Function
SGSN connect with MSC via Gs interface( optional)
Combined IMSI/GPRS attach/detach
Combined location area/routing area updating
Improve radio resource
GPRS support SMSGPRS support SMS
SGSN connect with SMSC via Gd interface
capable of sending SM by GPRS, thus decrease the influence to voice service
Share the existing short message information source
Transfer SMS by MSC or SGSN upon decision of operator
AgendaAgenda
GPRS Network Structure
GPRS Network interface and protocol
GPRS address and identity
GPRS radio interface technology
GPRS Mobility Management
GPRS Session Management
GPRS Network Structure
GPRS Network interface and protocol
GPRS address and identity
GPRS radio interface technology
GPRS Mobility Management
GPRS Session Management
GPRS Network StructureGPRS Network Structure
BTS SGSN GGSNBSC
MSC/VLR
Gi
Gn
GrGs
Gb
Gn
A
Abis
HLR
IPNetwork
GPRSBackbone
BGBG
Other PLMN
Gp
PCU
SGSN
GGSN
Gn
GnBGBG
SS7
Data Transmission PlatformData Transmission Platform
GSM RF
MAC
RLC
LLC
SNDCP
L1
NetworkService
BSSGP
LLC
SNDCP
MS BSS SGSNGbUm
IP
L2
IP
UDP/TCP
IP
UDP/TCP
GTP
L1bi s
NetworkService
BSSGP
GSM RF
MAC
RLC
Relay
IP IP
Gn Gi
RelayIP
Relay
Appli-cation
Appli-cation
GGSN ISP
L1
L2 L2
L1
L2
GTP
MS-BSS-SGSN Signaling PlatformMS-BSS-SGSN Signaling Platform
GMM: GPRS Mobility Management
SM: Session Management
MS BSS SGSN
BSSGP
GMM/SM
LLC
RLC
MAC
GSM RF
GMM/SM
LLC
BSSGP
L1bis
Um Gb
NetworkService
RLC
MAC
GSM RF L1bis
NetworkService
relay
Gb InterfaceGb Interface
BTS SGSNBSCGbAbis
PCU
L1bis : physical transmission layer, based on E1or T1
NS : transmit BSSGP PDU based on frame
BSSGP : provide link without connection for data transmission without acknowledgement ;
For signaling platform, transmit radio related information , such as QoS 、 routing ;
Process paging request , flow control to data transmission
L1/L2 : lower layer transmission networks :ATM,Ethernet,DDN
IP : backbone protocol, routing selection for data and control ;
UDP/TCP : UDP bear PDU no requiring reliable transmission;
TCP provide flow control and loss, error protection to bear PDU requiring reliable transmission
GTP : data and protocol transmission between GSN
Gn/GP interfaceGn/GP interfaceBTS SGSN GGSNBSC
Gn
Gb
Gn
Abis
GPRSBackbone
BGBGOther PLMN
Gp
PCU
SGSN
Gn
BGBG
SCCP
MTP2
MTP3
MTP2
MTP3
SCCP
GrGd
SGSN
TCAP
MAP
TCAP
MAP
L1 L1
No.7 Signaing InterfaceNo.7 Signaing Interface
Gr : Authentication, MM
Gd: transmit SM via GPRS network
HLRSMC
Submit SMS Submit SMS
SMSC check destination address of SMS,request location
information of relevant HLR
HLR return information include the current SGSN or MSC
number ,or both to SMS.
if no SGSN number ,means MS not reachable via SGSN;
SGSN is given priority to be chosen for SMS delivery
AgendaAgenda
GPRS Network Structure
GPRS Network Interface and Protocol
GPRS Address and Identity
GPRS Radio interface technology
GPRS Mobility Management
GPRS Session Management
GPRS Network Structure
GPRS Network Interface and Protocol
GPRS Address and Identity
GPRS Radio interface technology
GPRS Mobility Management
GPRS Session Management
SGSN GGSN
GPRS BackboneGPRS Backbone
PDP addressP-TMSIIMSI
TLLI/ NSAPI
IP address
No.7 signaling address
TID=IMSI+NSAPI
Address, IdentityAddress, Identity
TLLI/NSAPI used to uniquely identify PDP PDU of MS between
MS and SGSN ; TID used to uniquely identify PDP PDU of MS between GSNs;
used to forward user data with tunnel transmission mechanism, is
composed of IMSI/NSAPI, existed in head of GTP
IPNetwork
IP address
No.7 signaling address
P-TMSI : assigned by SGSN for attached GPRS user used in
PS, correspond to TMSI in CS;
TLLI : Identify logical link between MS and SGSN, deduct
from P-TMSI
NSAPI : used to specify specific PDP Context for MS
IMSI/NSAPI or NSAPI/TLLI in routing cell can be used
to uniquely identify specific PDP context for specific user.
TID : IMSI+NSAPI, used to uniquely identify a PDP context
between SGSN and GGSN, or new SGSN and old SGSN
Address, IdentityAddress, Identity
GSN address : every GSN has one or more IP address , internal
address , each one has one or more domain name for communication
GSN Number : Each SGSN has a SS7 numbering to communicate with HLR and MSC.
GGSN shall have a SS7 numbering as well if GGSN connect with HLR via Gc interface
PDP Address : IP address ( IP4 or IP6 ) or X.121 address
( for X.25 service )
Address ,IdentityAddress ,Identity
IP Address AllocationIP Address Allocation
In GPRS network, SGSN, GGSN,CG,DNS is communicated with each other by IP address, each NE shall be allocated one IP.
The IP address of SGSN,GGSN,DNS is private or public, which
need to be planned in whole GPRS network.
CG usually use private IP for safety purpose. MS shall be allocated IP address, IP address allocation :
Static address assigned to MS when subscription; or
dynamic address allocated to MS when PDP context activation;
IP address can be private or public;
If MS use private address, address mapping and conversion need to
be implemented by network when MS visit external IP network.
BSSInternetGPRS Backbone
DNS
SGSN GGSN
FireWare
10.2.1.1
10.2.1.2
202.1.1.1202.1.1.2 202.100.1.1
202.1.1.4
10.2.1.1 <-> 202.100.1.1:100110.2.1.2 <-> 202.100.1.1:1002
IP for NE interface ( Gn , Gi ) is public address ;
Mobile Terminal is allocated as private address ( dynamic )
IP Address AllocationIP Address Allocation
AgendaAgenda
GPRS Network Structure
GPRS Network Interface and Protocol
GPRS Address , Identity
GPRS Radio Interface Technology
GPRS Mobility Management
GPRS Session Management
GPRS Network Structure
GPRS Network Interface and Protocol
GPRS Address , Identity
GPRS Radio Interface Technology
GPRS Mobility Management
GPRS Session Management
Radio Channel Allocation Radio Channel Allocation
GPRS share the physical channel of radio
interface with GSM
Radio resource allocation :
Dynamic allocation
Fixed allocation
PS/CS Channel Dynamic AllocationPS/CS Channel Dynamic Allocation
P2 P1 P3 P3 P3 P3 P3 P3 P3P2 P1 P3 P4 P4 P5 C8 C8 C8P1 P1 P1 P4 P4 P5 C9 C9 C9P1 P1 P1 P1 P5 P5 P5 P5 P5C4 P1 P1 P1 P1 P1 P1 C10 C10C3 C3 C3 C3 C3 C3 C3 C3 C3C2 C2 C2 C6 C6 C6 C6 C6 P1C1 C1 C5 C5 C5 P5 C7 C7 C7
7时 隙
时 间21
0时 隙1时 隙2时 隙3时 隙4时 隙5时 隙6时 隙
83 75 64 9
P: Packet channel , C : voice channel
Coding Scheme For Radio ChannelCoding Scheme For Radio Channel
Higher data transmission rate of each timeslot is compensated by lower error-tolerance.
Scheme CodeRate
USFbits
Pre-codedUSFbits
RadioBlock(excl. USF
and BCS)
BCS Tailbits
Codedbits
Puncturedbits
DataRate
(kbps)
CS-1 1/2 3 3 181 40 4 456 0 9.05
CS-2 ~2/3 3 6 268 16 4 588 132 13.4
CS-3 ~3/4 3 6 312 16 4 676 220 15.6
CS-4 1 3 12 428 16 0 456 0 21.4
Add BCS(
Add precoded USF
Add tail bits Coding Puncture 456bits
Effective load
• BCS : Block Check Sequence
• USF : Uplink State Flag
Steps for GPRS codingSteps for GPRS coding
rate 1/2 convolutional coding
puncturing
456 bits
USF BCS
Radio Block
B0 B1 B2 T B3 B4 B5 X B6 B7 B8 T B9 B10 B11 X
52 TDMA Frames
12 Radio Block Periods = 240 ms
*Interleaving
Radio block structure from CS1 to CS3Radio block structure from CS1 to CS3
Radio Block Structure for CS4Radio Block Structure for CS4
blockcode
no coding
456 bits
USF BCS
Radio Block
*Interleaving
B0 B1 B2 T B3 B4 B5 X B6 B7 B8 T B9 B10 B11 X
52 TDMA Frames
12 Radio Block Periods = 240 ms
Channel Data Flow RateChannel Data Flow Rate
C/I 载干比 (dB)•CS1 and CS2 least influenced by carrier-to-interference radio
•CS3 and CS4 has low efficiency for low C/I, used when C/I >10 DB
0
5
10
15
20
25
0 4 8 12 16 20 24
CS1CS2CS3CS4
Typical city area, moving speed at 3km/h
User data
Segment Segment
Info FH FCS
PH
Segment Segment Segment
InfoBH BCS Tail
Convolutional encoding
Burst Burst Burst Burst
...
...
Network layer
SNDCP layer
SNDCP layer
LLC layerLLC layer
RLC / MAC layer
RLC / MAC layer
Physical layer
Packet(PDU)
LLC frame
RLC block
Normal Burst
PH : Packet Header BH : Block Header FCS : Frame Check SequenceFH : Frame Header BCS : Block Check Sequence LLC:Logic Link Control, RLC:Radio Link Control
456 bits
114 bits 114 bits 114 bits 114 bits
Data flow for Packet TransmissionData flow for Packet Transmission
AgendaAgenda
GPRS Network Structure
GPRS Network interface and protocol
GPRS Address, Identity
GPRS Radio Interface Technology
GPRS Mobility Management
GPRS Session Management
GPRS Network Structure
GPRS Network interface and protocol
GPRS Address, Identity
GPRS Radio Interface Technology
GPRS Mobility Management
GPRS Session Management
MS AttachMS Attach
Attach Type :When MS turn-on, initiate attach procedure, Attach Type included in Attach Request indicates the type
Log on GPRS onlyLog on GPRS/ Non-GPRS, SGSN initiate location update procedure to MSC/VLR MM Context :PMM has three states , can be converted under the trigger of different event , each state corresponds to certain functionality and a series of relevant information, which constitute MM context; one user corresponds to a unique MM context, which existed in MS and SGSN.
Idle GPRS connection
Or PDP activation
GPRS detach
Timer Timeout
Send or receive PDU
Timer
timeo
ut o
r loc
ation
canc
ellat
ion
MS State ModelMS State Model
Ready
CI is known
Standby
RAI is known
In GPRS, location management is based on RA. RA is a subset Of location area, a location area can be viewed as a RA, can also be defined as several RA. Every RA is served by one SGSN, location update includes:
Cell update; CI changes, RA unchanged;RA update: RAI changes, Intra-SGSN RA update Inter-SGSN RA updateCombined RA/LA update Intra-SGSN Combined RA/LA update Inter-SGSN Combined RA/LA updatePeriodical Location Update
Location ManagementLocation Management
Mobility Management enable the system acquire the user state info and location info.Includes:
GPRS Attachment: establish MM context, MM state changed to Standby state.GPRS Detachment: Delete MM context, MM state changed to IdleCan be initiated by MS or Network sideSafety function: authentication, encryption,identification check, etc.Location Management: RA update, periodical update, Cell update
Mobility Management FunctionMobility Management Function
MS BSS new SGSN HLRGGSNold SGSN
2. SGSN Context Response
3. Security Functions
1. Routeing Area Update Request
2. SGSN Context Request
6. Update PDP Context Request
6. Update PDP Context Response
7. Update Location
10. Update Location Ack
11. Routeing Area Update Accept
8. Cancel Location
8. Cancel Location Ack
9. Insert Subscriber Data Ack
9. Insert Subscriber Data
12. Routeing Area Update Complete
5. Forward Packets
4. SGSN Context Acknowledge
C1
C3
C2
Inter-SGSN Update
MS SGSN HLR
Insert Subscriber Data
Attach Request
. Update Location
Update Location AckInsert Subscriber Data Ack
Attach Accept
Triplet request
Authentication
GPRS MS Attachment ProcedureGPRS MS Attachment Procedure
AgendaAgenda
GPRS Network Structure
GPRS Network Interface and Protocol
GPRS Address, Identity
GPRS Radio Interface Technology
GPRS Mobility Management
GPRS Session Management
GPRS Network Structure
GPRS Network Interface and Protocol
GPRS Address, Identity
GPRS Radio Interface Technology
GPRS Mobility Management
GPRS Session Management
If GPRS service applied by a user involved in one or more than one external PDN( e.g. Internet,X.25), GPRS subscribed data shall include 如果一个用户所申请的 GPRS 业务涉及一个或多个外部PDN(如等),则在其 GPRS 签约数据中就将包括一个或多个与这些 PDN 对应的 PDP 地址。每个 PDP 地址对应有一个PDP 上下文。每个 PDP 上下文由 PDP 状态及相关信息来描述,存在于 MS 、 SGSN 、 GGSN 中。一个用户的所有PDP 上下文都与该用户唯一的一个 MM 上下文相关联。
Session Management-PDP Context Session Management-PDP Context
MS send “PDP activation request” to SGSNAPNPDP type (IP)PDP address requestQoS and others
SGSN check user dataAPNDynamic or static IP address
BTS BSC
SGSN
GGSN
Intranet
GPRS Core
Network
SS7
HLR
DNS
Internet
1.
AccessPoint
PDP Activation - 1PDP Activation - 1
Definition of APN Structure Definition of APN Structure
APN Network Identification define the external network GGSN connected (mandatory ) APN Operator Identification define the GPRS Network where GGSN located (optional)APN correspond to a GGSN domain name
www.zte.com.cn.mnc<MNC>.mcc<MCC>.gprs
APN Network Identification
APN Operator
Identification
BTS BSC
SGSN
GGSN
GPRS Core
Network
DNS
Intranet
Internet
1.
2.
AccessPoint
(1) SGSN obtain GGSN IP address from DNS
APN mapping GGSN IP address
(2) SGSN send “ create PDP context” request to GGSN
PDP type ( e.g.IP ) PDP address ( dynamic or
static ) APN QoS and other parameters
PDP Activation - 2PDP Activation - 2
BTS BSC
SGSN
GGSN
GPRS Core
Network
Intranet
Internet
1.
2.
APN identify external data network the user want to use Dynamic address allocation: allocated by GGSN address pool or external DHCP server GGSN return “create PDP context response” to SGSN SGSN return “PDP context activated”to MS SGSN can establish routing between MS and GGSN
PDP Activation - 3PDP Activation - 3
PDP Activation on Network side (1)
MS SGSN GGSN
3. PDU Notification Request
HLR
1. PDP PDU
2. Send Routeing Info for GPRS
2. Send Routeing Info for GPRS Ack
4. Request PDP Context Activation
5. PDP Context Activation procedure
3. PDU Notification Response
PDP Activation on Network side(2)
MS SGSN GGSN
PDU Notification Request
HLR
PDP PDU
Send Routeing Info for GPRS
Send Routeing Info for GPRS Ack
Request PDP Context Activation
PDP Context Activation procedure
PDU Notification Response
PLMN Backbone Network
Visiting Network Home Network
GPRS MS ClassificationGPRS MS Classification
Class ACan Attache GPRS and non-GPRS network, and implement the CS and PS service simultaneously.
Class BCan Attache to GPRS and GSM network, but can’t implement CS and PS service simultaneously.
Class CCan’t attach to GPRS and GSM network simultaneously, only one of them can be selected, unselected service state is in off state, which can be connected.
Procedure for MS Access to InternetProcedure for MS Access to Internet
Procedure: 3 steps Attach PDP activation Access to Internet
Attach_request (IMSI)
Triplet request
Authentication
Update_location
GPRS MS AttachGPRS MS Attach
SGSN HLR
Insert_subscriber_data
Update_location_ack
GPRS MS AttachGPRS MS Attach
Attach_accept (TLLI)
MS TLLI
SGSN HLR
Activate_PDP_context_req(NSAPI1,type [+ @ of PDP] , APN, QoS)
DNS_query (APN)
DNS_response (IP of GGSN)
DNS
PDP ActivationPDP Activation
SGSN
Create_PDP_context response (IP )
Activate_PDP_context_accept (IP )
Create_PDP_context_req(type, APN, QoS)
TID1 Create_PDP_ctxt GGSN IP
PDP ActivationPDP Activation
GGSNSGSN
GPRS MS Data TransmissionGPRS MS Data Transmission
TLLI IMSI
NSAPI + IMSI TID
NSAPI TLLI
NSAPITLLI User packet
User packet
User packetTIDGGSN
PDP network (IP/X.25)
GGSNSGSN
Roaming - Connected to Home GGSN
Roaming - Connected to Home GGSN
Home PLMN
GGSN
GGSN
BG
ISP Network
ISP Network
BG
MS SGSN
HLR
Visiting PLMN
RoamingMS
Re-attach
Subscriptiondata GTP addres-
sing
IPSectunnelhop-by-hop
SGSNMS
Home PLMN
GGSN
GGSN
BG
Home ISP Network
Home ISP Network
BG
MS SGSN
HLR
Visiting PLMN
RoamingMS
Re-attach Visiting ISP
Network Visiting ISP
Network
SGSN
RADIUS
RADIUS
Roaming agreement between ISP’s
MS
Roaming-Connected to Visiting GGSN
Roaming-Connected to Visiting GGSN
Th
ank
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