introduction-to-gprs-egprs-

EVOLIUM Base Station Subsystem
INTRODUCTION TO GPRS/EGPRS

TRAINING MANUAL
3FL10472ACAAWBZZA2 – MARCH 2006

© All rights reserved. Passing on and copying of this document,
use and communication of its contents not permitted without
written authorization from Alcatel.
© Alcatel University – 3FL10472ACAAWBZZA Ed.02

Page 1

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Copyright

1

This document contains information that is proprietary to Alcatel and may be used for training purposes
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2
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All rights reserved © 2004, Alcatel
legislation is hereby expressly prohibited.

Introduction to GPRS/EGPRS

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.

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equipment and its operation.


Page 2

Contents
1 What is GPRS ?

6

1.1 Definition

8

1.2 General architecture

9

1.3 MS Class

10

1.4 MS Multislot Class

11

1.5 GPRS Main Concepts

12

1.6 The benefits of GPRS

17

1.7 EGPRS

18

1.8 Quality of service profile

19

1.9 Services

20

2 GPRS Operation

23

2.1 Main Entities

25

2.2 MS Mobility Management States

30

2.3 MS Radio Resource Operating Modes

31

2.4 Basic procedures

32

2.5 Charging

45

2.6 Security

47

3 The Base Station Subsystem

52

3.1 3GPP Position

54

3.2 Alcatel’s Choice

55

3.3 Layered Model

56

3.4 Gb Interface

58

3.5 Radio Interface

60

4 Alcatel Solution

71

4.1 GPRS Network Overview

73

4.2 Alcatel 9135 MFS

74

4.3 Packet Switched Core Network

80

4.4 GPRS Network Management

82

4.5 Alcatel QoS offer

83

5 Annex and Glossary


88

Page 3

Self assessment of the objectives

Contract number :

Course title :
Client (Company, centre) :
Language : English

dates from :

Number of trainees :

to :

Location :

Surname, First name :

Did you meet the following objectives ?
Tick the corresponding box
Please, return this sheet to the trainer at the end of the training

Yes (or
Globally
yes)

Instructional objectives
1

To be able todescribe the organization of a
GPRS network,architecture, interfaces and
protocols.

3

To be able todescribe the main data
interchange mechanisms on a GPRS
network

4

Comments

To be able toidentify the benefits of GPRS

2

No (or
globally
no)

To be able tocharacterize the solution
offered by Alcatel

Other comments


Page 4

Self assessment of the objectives (continued)
Yes (or
Globally
yes)

Instructional objectives

No (or
globally
no)

Comments

Other comments

Thank you for your answers to this questionnaire


Page 5


Page 6

1 What is GPRS ?
Session presentation
> Objective: to be able to identify the technical
and commercial benefit of GPRS.
> Program:
• 1.1 Definition
• 1.2 General architecture
• 1.3 MS Class
• 1.4 MS Multislot Class
• 1.5 GPRS Main Concepts
• 1.6 GPRS Benefits
• 1.7 EGPRS
• 1.8 Quality of Service profile
• 1.9 Services

7


Page 7

1 What is GPRS ?
1.1 Definition
> Definition (3GPP TS 22.060)
• GPRS provides data transfer capabilities between a sending entity and
one or more receiving entities.
• These entities may be an MS or a Terminal Equipment, the latter being
attached either to a GPRS network or to an external data network.
• The base station provides radio channel access for MSs to the GPRS
network.


8

w PDN (Packet Data Network)
IP networks = Internet (connectionless)


Page 8

1 What is GPRS ?
1.2 General architecture
RADIO
ACCESS
NETWORK

circuit
switching

A

PSTN

NSS

BSS
GPRS
Gb

PDN

Core Network
IP

IP / PPP

Packet
switching


Gi

9

w GPRS Core Network
The GPRS Core Network is also called GSS (GPRS Sub-System). It is an IP network, and therefore contains routers
(machines handling the packet switching function.)
w Routing Function
Data transmission between GPRS Support Node (GSN), may occur across external data networks that provide their own
internal routing functions, for example X.25 [34], Frame Relay or ATM networks.
w IP interworking
The GPRS Core Network supports interworking with networks based on the Internet protocol (IP). The GPRS Core
Network may provide compression of the TCP/IP header when an IP datagram is used within the context of a TCP
connection.
w X.25
X.25 PDP Type have been removed from the standard since R99.


Page 9

1 What is GPRS ?
1.3 MS Class
> Class A
• Operates GPRS and other GSM services simultaneously.

> Class B
• Monitors control channels for GSM GPRS and other GSM services
simultaneously,
• but can only operate one set of services at one time.

> Class C
• Exclusively operates GPRS services.


10

w Classes A and B
Require dual scanning by the mobile for both GSM and GPRS service requests. Class A or B mobiles are "attached"
simultaneously to both networks.
w Class B
The exchange of packets is suspended to answer to an incoming GSM call (the GPRS subscriber is considered to be in
the "busy" or “on hold" state).
The PDP contexts are still active on the SGSN side until the Purge_Timer elapses.
w Class C
Exclusively operates GPRS services.


Page 10

1 What is GPRS ?
1.4 MS multislot class
Multi-slot
class
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19 to 29
like 10

Type

Rx

Tx

Sum

Ttb

Tra

Trb

1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2

1
2
2
3
2
3
3
4
3
4
4
4
3
4
5
6
7
8

1
1
2
1
2
2
3
1
2
2
3
4
3
4
5
6
7
8

2
3
3
4
4
4
4
5
5
5
5
5
NA
NA
NA
NA
NA
NA

2
2
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0

4
3
3
3
3
3
3
2
2
2
2
2
3
3
3
2
1
0

2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
0
0

1

x

x

NA


11

w MS type
Type 1 are simplex MS, i.e. without duplexer: they are not able to transmit and receive at the same time
Type 2 are duplex MS, i.e. with duplexer: they are able to transmit and receive at the same time
w Rx
Maximum number of received timeslots that the MS can use per TDMA frame. The receive TS shall be allocated
within window of size Rx, but they need not be contiguous. For SIMPLEX MS, no transmit TS shall occur between
receive TS within a TDMA frame. This does not take into account measurement window (Mx).
w Tx
Maximum number of transmitted timeslots that the MS can use per TDMA frame. The transmit TS shall be
allocated within window of size Tx, but they need not be contiguous. For SIMPLEX MS, no receive TS shall occur
between transmit TS within a TDMA frame.
w SUM
Maximum number of transmit and receive timeslot (without Mx) per TDMA frame
w Meaning of Ttb, Tra et Trb changes regarding MS types.
For SIMPLEX MS (type 1):
Ttb Minimum time (in timeslot) necessary between Rx and Tx windows
Tra Minimum time between the last Tx window and the first Rx window of next TDMA in order to be able to
open a measurement window
Trb same as Tra without opening a measurement window
For DUPLEX MS (type 2):
Ttb Minimum time necessary between 2 Tx windows belonging to different frames
Tra Minimum time necessary between 2 Rx windows belonging to different frames in order to be able to
open a measurement window
Trb same as Tra without opening a measurement window


Page 11

1 What is GPRS ?
1.5 GPRS Main Concepts (1/5)
> Use of radio resources in case of circuit switching
Radio interface

Access node
<CS <->PS
Radio timeslot

GSM
network
CS

PDN
PS

Fixed Rate

12

w Drawbacks of CS for data services
one radio channel at 9.6 kbit/s per user
fixed bit rate => waste (in the case of discontinuous service) and limitation on bit rate


Page 12

1 What is GPRS ?
> Use of radio resources in case of packet switching
Radio interface

GPRS

PDN

network

PS

PS
Radio timeslot

Variable Rate

13

w Benefits of Packet Switching
Variable bit rate becomes possible
One MS uses several RTSs. The maximum number of RTSs is given by the Operator (O&M parameters) and MS
capabilities (MS multislot class)
One RTS is shared by several MSs. The maximum number of MSs per RTS is given by the Operator (O&M
parameters) and 3GPP specifications (limitation due to addressing availability)


Page 13

1 What is GPRS ?
> Radio resource assigned according to requirement
• Radio resource shared between users
• Various radio channel coding schemes are specified to allow bit rates
from 9 to more than 150 kb/s per user (according also to the quality of
radio transmission and the modulation used)
• High bit rates if several channels are assigned to one MS
• Low bit rates if one channel is shared by several MSs.

> Optimized use of the radio resource
• Use of the radio resources only when data is transferred
• Uplink and downlink resources reserved separately


14

w Radio resource sharing
The radio resources are shared by statistical multiplexing. As in GSM, no subscriber has their own permanent radio
resource.
w Bit rate
Maximum instantaneous bit rate provides 171,2 kb/s by the allocation of eight RTSs to one subscriber. The stated
maximum bit rates are different, because different coding schemes are used, which impacts the bit rate over a RTS. (see
Annex)
w Up link (UL) and downlink (DL)
It is possible to use a different bit rates in each transmission direction, whereas in CS (Circuit Switching) mode, there is a
maximum limit of 9.6 kb/s, in both directions and at all times.


Page 14

1 What is GPRS ?
> Dynamic allocation and sharing of radio resources
1 RESOURCE USED BY ONE USER NOT SHARED TCH
User 1
User 1
User 2
User 3
User 4
User 5

1 RESOURCE SHARED BY X USERS (PDCH)

USER1 USES 3 RESOURCES (3 PDCH)

User 1

Number of resources according to the capability of the MS

15

w Caution: Animated slide that does not make sense if not in the slide-show mode.
w Optimized use
A radio resource (set of Radio Blocks over one or several RTS) is allocated only when data is being transferred, by
establishing and releasing Temporary Block Flow (TBF), that can be presented as micro-connections, each time a data
transfer has to be sent over the radio interface.
w Radio resource sharing
One TS can be shared by several MSs, by dynamic time multiplexing under control of the BSS.


Page 15

1 What is GPRS ?
> Variable useful transmission rate per Radio resource
When the radio transmission has a good quality the security can be reduced in
order to increase the useful transmission rate

Maximum security

Minimum security

Channel Transmission rate
about 22 k with GMSK
about 60k with 8PSK (Edge)

minimum throughput

Maximum throughput

16


Page 16

1 What is GPRS ?
1.6 The benefits of GPRS
> GPRS benefits
• BSS hardware (included OMC-R) is re-used from GSM
• Smooth GPRS introduction
• Higher data throughput thanks to EGPRS (EDGE)
• Data transfers can billed by volume instead of time
• An MS can exchange data by GPRS in parallel with a conventional GSM
call (if MS Class A)


17

w BSS is re-used
The same Radio Access Network is re-used, and a Packet Control Unit (PCU) function is implemented in the BSS.
w Compared to the GSM BSS
same frequency bands
same TDMA frame structure
same burst structure
same frequency hopping laws
...


Page 17

1 What is GPRS ?
1.7 EGPRS
> EGPRS is an enhancement of GPRS
• allows higher bit rates on the radio interface
• achieved by using
–
–

a new modulation (8-PSK)
and new coding schemes (MCS-1 to MCS-9) in the MS and the BSS.

> The same set of services provided by GPRS is available in EGPRS.


18

w Shared = in other words: "the radio resources are shared by statistical multiplexing". As in GSM, no subscriber has their
own permanent radio resource.
w High or low bit rates = more than one time slot per MS or conversely, more than MS on the same TS (one TDMA frame
occupies 4.615 ms and is divided into 8 TS or channels).
w Maximum instantaneous bit rate provided = 171,2 kbps through the allocation of eight TSs to one subscriber. The stated
maximum bit rates are different (according to the BSS release), because different ways of encoding the data, or "coding
schemes", are used, which impacts the bit rate over a TS. (cf Annex)
w Optimized use:refer to Radio resource allocation in the slides to come + radio resource management in the BSS
Chapter.The radio resource allocation is suitable for variable, bursty traffic (downloading Web pages).
w Up link (UL) and downlink (DL): It is possible to use a different bandwidth (bit rate) in each transmission direction, whereas
in CS (circuit switching) mode, there is a maximum limit of 9,6 kbps, in both directions and at all times.
w QoS: Henceforth, QoS parameters are part of subscription data, according to the wide range of services provided to a
subscriber.


Page 18

1 What is GPRS ?
1.8 Quality of service profile
9 classes
19 classes

5 classes
4 classes
3 classes

Peak throughput Class
the maximum data rate allowed to the user

Throughput class

Mean throughput Class
maximum data rate during a period

Reliability Class
acknowledgement of packets

Delay Class
total delay measured between R or S point and Gi

Precedence Class
relative importance of service under congestion


19

w Precedence class
According to the class, user data packet can be discarded during the transfer due to a congestion state.
3 classes are defined : any, normal, high
w Delay class
The delay class depends on the operator network because a measurement is done between the R or S interface (between
the Mobile Terminal and the Terminal Equipment) and the Gi interface. For each operator, delay values are different so
delay classes are a reference not a strict value.
4 classes are defined : best effort, 1, 2, 3
w Reliability class
The reliability means that user data packets are acknwoledged during the transfer. The reliability classes are defined
according to the acknowledgement or not of the packet.
5 classes are defined
w Throughput class
The throughput class is defined by the 2 following parameters:
Mean Throughput : 9 classes are defined (from best effort to 111 Kb/s)
Peak Throughput : 19 classes are defined (from 8 Kb/s to 2048 Kb/s)


Page 19

1 What is GPRS ?
1.9 Services
Media

Always-on

Fun
• Games (Hangman, Poker, …)
• Screen Saver
• Ring Tone
• Horoscope
• Biorhythm

Directories
• Yellow/White Pages
• International Directories
• Operator Services

Mobile Office
• Voice (!)
• E-mail
• Agenda
• IntraNet/InterNet
• Corporate Applications
• Database Access

Music
• Downloading of
music files or
video clips

Transportation
• Flight/train Schedule
• reservation

Vertical application
•Traffic Management
•Automation
•Mobile branches
•Health

News
(general/specific)
• International/National News
• Local News
• Sport News
• Weather
• Lottery Results
• Finance News…

• Traffic Conditions
• Itineraries
• Nearest Restaurant,
Cinema, Chemist,
Parking;, ATM ...

M-commerce
Non physical
• on-line Banking
• Ticketing
• Auction
• Gambling….


Location services

Physical
• on-line shopping
• on-line food

20

w Retrieval services
Provide the capability of accessing information stored in data base centers. The information is sent to the user on demand
only. An example of one such service in the Internet's World Wide Web (WWW).
w Messaging services
Offer user-to-user communication between individual users via storage units with store-and-forward mailbox, and/or
message handling (e.g., information editing, processing and conversion) functions;
w Conversational services
Provide bi-directional communication by means of real-time (no store-and-forward) end-to-end information transfer from
user to user. An example of such a service is the Internet's Telnet application;
w Tele-action services
Characterized by low data-volume (short) transactions, for example credit card validations, lottery transactions, utility meter
readings and electronic monitoring and surveillance systems.
w Distribution services
Characterized by the unidirectional flow of information from a given point in the network to other (multiple) locations.
Examples may include news, weather and traffic reports, as well as product or service advertisements;
w Dispatching services
Characterized by the bi-directional flow of information from a given point in the network (dispatcher) and other (multiple)
users. Examples include taxi and public utility fleet services;
w Conferencing services
Provide multi-directional communication by means of real-time (no store-and-forward) information transfer between
multiple users.


Page 20

1 What is GPRS ?
Exercise
–

True or False ?
–
–
–
–
–
–
–
–
–

GPRS is a circuit switching technology
The GSS is an IP network
Data transfers are often conducted at variable bit rates
With a class B mobile, a web page can be downloaded while speaking
Billing by volume allows subscribers to be permanently on line
Several channels can be assigned to a MS
One channel is shared by several MSs
EGPRS is GPRS with better Throughput
The useful transmission rate depends on the radio quality

Time allowed :
5 minutes


21


Page 21

1 What is GPRS ?
Evaluation
> Objective : to be able to identify the
technical and commercial benefit of GPRS

Thank you for answering
the self-assessment
of the objectives sheet


22


Page 22

2

GPRS Operation



Page 23

2 GPRS Operation
> Objective: to be able to describe the organization of a
GPRS network architecture, interfaces and protocols.
> Program:
• 2.1 Main Entities
• 2.2 MS Mobility Management States
• 2.3 MS Radio Resource Operating Modes
• 2.4 Basic Procedures
• 2.5 Charging
• 2.6 Security


24


Page 24

2 GPRS Operation
2.1 Main Entities
> Overview

To PSTN

PCU included
in BSS
BTS

AUC

BSC

EIR

circuits
CELLS

MSC
VLR

N7

HLR

NSS CALL PROCESSING

BSS RADIO ACCESS

NTP

DNS

SGSN

GGSN

To IP Networks

IP

GPRS

BG

SGSN
DHCP

To other operator
IP Networks

25



w PCU functions
LLC PDU segmentation / re-assembly into RLC/MAC PDU
PDCH scheduling (resource multiplexing)
Channel access control (access requests and grants)
ARQ function (RLC block Ack / Nak, buffering and retransmission of RLC blocks)
Radio channel management (power control, congestion control, broadcast control information).
w DNS (Domain Name Server) and DHCP (Dynamic Host Convergence Protocol)
w NTP server (Network Time Protocol) for GSN synchronization. In general an NTP application does not run on a
dedicated server. The OMC-G can play this role.
w HLR (Home Location Register) is involved in MS attachment to the GPRS network (authentication + services subscribed
to)


Page 25

2 GPRS Operation
2.1 Main Entities
> SGSN and GGSN
IP
network 1

SGSN1
GGSN1

IP
network 1

SGSN2

IP

IP
network 1

backbone

SGSN3

GGSN2
IP
network 1

SGSN4

IP
network 1
SGSN5

GGSN3

GSS
26



w The SGSN (Serving GPRS Support Node) stores subscriber data:
Subscription information
IMSI
one or more temporary identities (P-TMSI)
zero or more PDP addresses
Location information
the cell or the RA where the MS is registered
the VLR number of the associated VLR (if the Gs interface is implemented)
the GGSN address of each GGSN for which an active PDP context exists
It also manages:
the transfer and routing of user data packets from the GSS towards the BSS
the mobility (GPRS attach/detach, data retrieval from the HLR, RA / Cell update)
the authentication and encryption (Access control and security)
the sessions (PDP context activation/deactivation)
The transfer of charging data.
w The GGSN (Gateway GPRS Support Node) stores subscriber data received from the HLR and the SGSN:
Subscription information
IMSI
zero or more PDP addresses
Location information
the SGSN address of the SGSN where the MS is registered
It also manages:
the allocation and use of dynamic @IP for MS,
the tunneling and encryption of user data at Gi interface,
the transfer of user data packets,
the charging data.

Page 26

2 GPRS Operation
2.1 Main Entities
> Servers
NTP

SGSN

GGSN

Alcatel.fr
256.167.123.34

DNS

GPRS
BACKBONE

DHCP

IP add

27



w DNS
Resolve a name into an IP address
Use in Mobility procedure
w DHCP
Provide dynamically IP addresses
Split Users into pool of IP addresses
w NTP
Provide one time reference for all the network
Have a very precise time reference
Synchronization from satellite


Page 27

2 GPRS Operation
2.1 Main Entities
> Border gateway
VISITED PLMN
BSS

SGSN

GGSN

VPLMN
BG

MS

INTER PLMN
NETWORK

HOME PLMN

BG
HPLMN

GGSN

PDN

28



w Border Gateway functions
Inter-PLMN routing and forwarding of user packets (IP router)
Security functions (firewall, access-list filtering)
w Connection of two Border Gateways
Via a private or public IP network, through the Gp interface.
w Choice of GGSN
If a subscriber wants to access an Intranet (PDN) in his home country, from the visited PLMN, the selected GGSN is the
one from the home PLMN
For Internet access a GGSN in the visited country could be used.


Page 28

2 GPRS Operation
2.1 Main Entities
> Interfaces
Um
Mobile
GPRS

BSS

A

MSC

Gs
Gb

SMSGMSC

HLR

Gd

Gr

Gc
SGSN
Gn

Signaling + data
Signaling

Gi

SGSN

GGSN

PDN

GPRS network

29



w Signaling protocols
MAP/TCAP/SCCP/MTP on Gr, Gd and Gc,
GTP/UDP/IP on Gn,
BSSAP+/SCCP/MTP on Gs,
GMM/SM/LLC on Gb/Um.
w Gc interface
Used for network-requested PDP contexts activation (GGSN asks the HLR for SGSN routing information).
w Gs interface
Defines the Network Mode of Operation I (NMOI). It allows to perform LA + RA combined Location Update, and PS and
CS paging coordination (refer to ANNEX).
w Gr interface
Exchange of subscription information at GPRS attachment phase
w Additional interfaces
Gf (to the EIR)
Gd to deliver the SMS to the mobiles via the GPRS network (SGSN option and subscriber feature)


Page 29

2 GPRS Operation
2.2 MS Mobility Management States
Autonomous cell reselection

> MS MM states

READY
timer expiry

Stand-by

Location at
CELL level

Location at
RA level
PDU transmission

Ready
GPRS Attach
Autonomous cell reselection NCO
Or controled by network
NC 2
( In paquet transfert mode )
GPRS Detach

Idle

30

w IDLE (GPRS) State
In GPRS IDLE state, the subscriber is not attached to GPRS mobility management. The MS and SGSN contexts hold no
valid location or routeing information for the subscriber. The subscriber-related mobility management procedures are not
performed.
Data transmission to and from the mobile subscriber and the paging of the subscriber is not possible. The GPRS MS is
seen as not reachable in this case.
In order to establish MM contexts in the MS and the SGSN, the MS shall perform the GPRS Attach procedure.
w STANDBY State
In STANDBY state, the subscriber is attached to GPRS mobility management. Pages for data or signalling information
transfers may be received. It is also possible to receive pages for the CS services via the SGSN. Data reception and
transmission are not possible in this state.
The MS performs GPRS Routeing Area (RA) and GPRS cell selection and re-selection locally. The MS executes mobility
management procedures to inform the SGSN when it has entered a new RA. The MS does not inform the SGSN on a
change of cell in the same RA. Therefore, the location information in the SGSN MM context contains only the GPRS RAI
for MSs in STANDBY state.
The MS may initiate activation or deactivation of PDP contexts while in STANDBY state. A PDP context shall be activated
before data can be transmitted or received for this PDP context.
w READY State
In READY state, the SGSN MM context corresponds to the STANDBY MM context extended by location information for the
subscriber on the cell level. The MS performs mobility management procedures to provide the network with the actual
selected cell. GPRS cell selection and re-selection is done locally by the MS, or may optionally be controlled by the
network.
An identifier of the cell, the Cell Global Identity including RAC and LAC, is included in the BSSGP header of the data
packet from the MS; see GSM 08.18 [21].
The MS may send and receive PDP PDUs in this state. The network initiates no GPRS pages for an MS in READY state.
Pages for other services may be done via the SGSN. The SGSN transfers downlink data to the BSS responsible for the
subscriber's actual GPRS cell.
The MS may activate or deactivate PDP contexts while in READY state.


Page 30

2 GPRS Operation
2.3 MS Radio Resource Operating Modes
> MS RR operating modes vs MS MM states
RR

Packet
transfer mode

MM

Packet
idle mode
Ready

Packet
idle mode
Standby

> Packet idle mode
In packet idle mode no Temporary Block Flow. Upper layers can require the
transfer of a LLC PDU which, implicitly, may trigger the establishment of TBF and
transition to packet transfer mode.
> Packet transfer mode
In packet transfer mode, the mobile station is allocated radio resource providing a
Temporary Block Flow (TBF) on one or more physical channels. Continuous
transfer of one or more LLC PDUs is possible. Concurrent TBFs may be established
in opposite directions. Transfer of LLC PDUs in RLC acknowledged or RLC
unacknowledged mode is provided.

31

w Packet idle mode
While operating in packet idle mode, a mobile station belonging to GPRS MS class A may simultaneously enter the different
RR service modes. A mobile station belonging to either of GPRS MS class B or C leaves both packet idle mode and
packet transfer modes before entering dedicated mode, group receive mode or group transmit mode.
w Packet transfer mode
When selecting a new cell, mobile station leaves the packet transfer mode, enters the packet idle mode
where it switches to the new cell, read the system information and may then resume to packet transfer mode in the new
cell.
While operating in packet transfer mode, a mobile station belonging to GPRS MS class A may simultaneously enter the
different RR service modes. A mobile station belonging to either of GPRS MS class B or C leaves both packet idle mode
and packet transfer modes before entering dedicated mode, group receive mode or group transmit mode.


Page 31

2 GPRS Operation
2.4 Basic Procedures
> IP overview
http

ftp

wap

smtp

http

ftp

smtp

wap

gtp
tcp

1

1

tcp

Routers
ip

ip

SGSN

ip

ip

ip

IP network
GGSN


32


Page 32

2 GPRS Operation
nK bytes MESSAGE

L4
L3

L2

x 4k TCP packets
TCP 4K bytes PACKET

IP

TCP

IP

TCP 4K bytes PACKET

Y Datagrams IP
IP

IP

TCP


Z Ethernet 1.5k frames
33


Page 33

2 GPRS Operation
IP / X25
SNDCP
SNDCP
LLC

HEADER

DATAS

HEADER

DATAS

HEADER

DATAS

HEADER

DATAS

CRC

Max 1600Bytes

SGSN to MS

RLC/
PCU

HEADER

TRE / CCU

456
456

AIR INTERFACE

57 X 8
57

57


34


Page 34

2 GPRS Operation
> Transmission plane
TCP HTTP FTP SMTP

Application

IP

IP

relay

SNDCP

SNDCP

LLC

LLC

GTP

GTP
UDP

UDP

IP

IP

L2

L2

Physical
layer

Physical
layer

relay
RLC

RLC

BSSGP

MAC

MAC

(Frame
Relay)

Physical
layer

Physical
layer

(Frame
Relay)

Physical
layer

Um

L2
MAC

BSSGP

Physical
layer

BSS
(with PCU)

MS

IP

SGSN

Gb

Physical
layer

GGSN

Gn

Gi

35

w GTP (GPRS Tunnelling Protocol) tunnels user data between GPRS Support Nodes in the backbone network. The GPRS
Tunnelling Protocol shall encapsulate all PDP PDUs.
w UDP (User Datagram Protocol) carries GTP PDUs for protocols that do not need a reliable data link (e.g., IP), and
provides protection against corrupted GTP PDUs.
w IP (Internet Protocol) is the backbone network protocol used for routing user data and control signalling. The backbone
network may initially be based on the IPv4. Ultimately, IPv6 shall be used.
w SNDCP (SubNetwork Dependent Convergence Protocol ) maps network-level characteristics onto the characteristics of
the underlying network.
w LLC (Logical Link Control) provides a highly reliable ciphered logical link. LLC shall be independent of the underlying
radio interface protocols in order to allow introduction of alternative GPRS radio solutions with minimum changes to the
NSS.
w Relay. In the BSS, this function relays LLC PDUs between the Um and Gb interfaces. In the SGSN, this function relays
PDP PDUs between the Gb and Gn interfaces.
w BSSGP (Base Station System GPRS Protocol) conveys routing and QoS-related information between the BSS and the
SGSN. BSSGP does not perform error correction.
w (NS) Network Service transports BSSGP PDUs. NS is based on the Frame Relay connection between the BSS and the
SGSN, and may - multi-hop and traverse a network of Frame Relay switching nodes.
w RLC/MAC (Radio Link Control / Medium Access Control). The Radio Link Control function provides a radio-solutiondependent reliable link. The Medium Access Control function controls the access signalling (request and grant) procedures
for the radio channel, and the mapping of LLC frames onto the GSM physical channel.


Page 35

2 GPRS Operation
> MS high protocol layers
GMM/SM

SMS

IP
NSAPIi

SNDCP

TLLI

LLC

NSAPI

TLLI

NSAPI

Radio layers

36



w SNDCP (Sub-Network Dependent Convergence Protocol)
Data compression, segmentation of large packets, recognition of PDP-PDU sessions (according to their NSAPI), inclusion
of QoS (use of SAPIs on the LLC link).
w NSAPI (Network Service Access Point Identifier)
This is used for a particular MS to distinguish different PDP contexts (= sessions)
by the PDP-type: X.25 or IP, or mainly by
the APN to be reached, or by
the required QoS.
w LLC (Logical Link Control)
Provides a safe link, encrypted and independent of the physical bearer, independent to BSS brand.
w TLLI (Temporary Logical Link Identity)
Identifies a logical link with the MS (one TLLI per MS)
w GMM/SM (GPRS Mobility Management / Session Management)
MS-SGSN signaling protocol for Gprs Mobility Management/ Session Management
w SMS (Short Message Service)


Page 36

2 GPRS Operation
> HLR GPRS data
For each MS
NMC-NSS

¨IMSI & MSISDN
¥ network access mode :
GPRS | NSS | both
¥ subscribed « PDP contexts » (maximum of n) :
• PDP type :

IP

| PPP

• [PDP address (IP@) ]

MS

HLR

• Access point name (APN) or * (= wild card)

n
times

• APN accessible through FPLMN-GGSN ?
• QoS profile

• etc ...
HPLMN


37

w PDP address
Almost always empty. The network then dynamically assigns (using a DHCP server) an IP address to the subscriber when
he activates his PDP context (seen later).
w PDP contexts
Each PDP context can be considered as a BS (basic service = telephony, fax, etc). A PDP context is a dialog session with
an external IP network, identified with an APN. It is not always mandatory to subscribe (in the HLR) to PDP contexts,
access to some networks is free. For a user, the traffic of his different sessions will be recognized in the messages by the
use of different NSAPIs. A user can declare one of his PDP contexts as the default.
w APN (Access Point Name)
The APN represents an IP network. An APN has two parts: the APN-Network Id (example: wanadoo.fr) and the APN-oper
Id (example: mnc...gprs)
Examples of APN: wanadoo.fr.mnc001.mcc208.gprs,
APN = * (wildcard) potentially authorizes the MS to activate any APN.
w Valid APN
Boolean, if YES, indicates that this APN can be reached through the GGSN of the visited FPLMN.


Page 37

2 GPRS Operation
> GPRS attachment

HLR

Update_loc_ack()

MS_authentication_procedure

GGSN

~

}

Ž

Œ

Insert_subs_data()

PLMN

N7

Update_loc_req()

Authent_info_req()

Attach-Request
(IMSI)

|

Authent_info_respq)

SGSN

Attach_resp (P_TMSI)

GPRS IP
backbone

Attach_complete () €
BSS
38



w Attach Request.
The attach_request message is placed in an LLC frame. x
The MS sends its IMSI.
w Authentication
The SGSN gets the “authentication triplets” from the HLR:
triplets request message y
triplets response message z
The SGSN performs the “authentication procedure” with the MS: {
triplets request message y
triplets response message z
w Location Update
The SGSN performs the “location_update procedure” with the HLR:
location_update request message |
the HLR transfers the MS_subscription data to the SGSN }
the HLR terminates the location_update procedure ~
w Attach Complete
The SGSN terminates the attach_procedure with the MS :
attach_accept message (with a new P_TMSI allocation)
attach_complete message € (since a new P_TMSI has been allocated)


Page 38

2 GPRS Operation
> GPRS attachment
After a GPRS_Attach procedure The mobile is « connected » to the serving SGSN

TLLI1

GGSN
1

SGSN
1

PDN 1

GPRS IP
backbone

SGSN
2

LLC layer


GGSN
2

PDN 2

GPRS - CN

39

w Attached MS
After running the attach procedure, the MS is “GPRS_attached”:
a logical connection is established between the MS and the SGSN
connection established between the peer LLC layers in the MS and the SGSN
this connection is identified by the TLLI (Temporary Logical Link Identity)
this logical connection remains established until the MS detaches
the MS can now access to GPRS services and is reachable for GPRS services


Page 39

2 GPRS Operation
> PDP context activation
DNS

DHCP

2
Activate_PDP_req (PDN2)

PLMN

4

Œ

TLLI1

GGSN

PDN
1

GPRS

SGSN

backbone

GGSN

Activate_PDP_resp(@IP_MS)
}

PDN
2

Create_PDP_req (PDN2) 3
BSS
5 Create_PDP_resp (@IP_MS)

GPRS Core Network


40

w MS IP address
In case of IP PDP_type access with no additional mobile authentication procedure, the MS IP address is provided by the
PLMN, using either the subscription data, or the backbone DHCP server. No additional user authentication is needed on
top of the GPRS authentication mechanisms (i.e. using IMSI and authentication triplets)
w PDP Context Activation
Œ MS requests for a PDP_context activation, providing the name of target Packet Data Network (PDN2
parameter).
SGSN queries the backbone Name Server (here DNS) to identify the GGSN giving access to the Data Network
PDN2 (here GGSN2).
Ž SGSN sends a Create_PDP message to the corresponding GGSN2, in order to setup a GTP tunnel.
GGSN2 allocates an IP address to the MS (@IP_MS), using the backbone DHCP server.
GGSN2 acknowledges the Create_PDP message to the SGSN, returning the @IP_MS allocated to the MS.
‘ SGSN acknowledges the Activate_PDP message to the MS, with the allocated @IP_MS.


Page 40

2 GPRS Operation
Authentication and
accounting

DNS
2

PLMN

Activate_PDP_req (PDN2)

RADIUS

Œ

TLLI1

GGSN
SGSN

4

GPRS
backbone

Activate_PDP_resp(@IP_MS)
}

ISP
INTRANET

GGSN
Create_PDP_req (PDN2) 3

BSS

6 Create_PDP_resp (@IP_MS)

GPRS Core Network

5

DHCP

Address allocation

41

w MS address
IP PDP_type access with mobile authentication via a RADIUS. The address allocation server (i.e. DHCP) and/or
authentication server (i.e. RADIUS) may be located within the PLMN or in the ISP/Intranet network. Non-transparent
access is aimed for corporate intranet access, where additional user authentication is often required.
w PDP Context Activation
The authentication data are piggybacked in the Protocol Configuration Options (PCO) field of the PDP context
activation messages Œ and ’.
Œ , , Ž same as for IP PDP_type in transparent access.
GGSN performs the user authentication towards a RADIUS server.
GGSN allocates an @IP to the MS using the intranet/ISP DHCP server.
‘, ’ same as for a PDP context in transparent access.


Page 41

2 GPRS Operation
after PDP_context_activation procedures
LLC layer

by the GTP layer

TLLI1

SGSN TID 1 = IMSI + NSAPI 1
1
TID
2

=I
MS
GPRS IP
I+
backbone
NS
AP

SGSN
2

GGSN
1

PDN 1

I2

GGSN
2

PDN 2

GPRS - CN


42

w User data transfer
In order to achieve a proper transfer of User Data, two main protocols are used: GTP (between GGSN and SGSN) and
LLC (between SGSN and MS), and two types of logical connections are established:
MS <-> SGSN. Logical Link used for signaling and data transfer, created at GPRS attach (unique per MS),
identified by a TLLI value;
SGSN <-> GGSN. Created with the activation of PDP context = when opening a session (several per MS),
identified each by a TID value.
w TLLI (Temporary Logical Link Identity)
Identifies uniquely a MS attached to the GPRS core network (Standby or Ready state).
w TID (Tunnel Identity)
Identifies a logical connection ("tunnel") between GGSN and SGSN (for each session of each MS). TID= IMSI+NSAPI.


Page 42

2 GPRS Operation
after PDP_context_activation procedures
LLC layer

by the GTP layer

TLLI1

SGSN TID 1 = IMSI + NSAPI 1
1
TID
2

=I
MS
GPRS IP
I+
backbone
NS
AP

SGSN
2

GGSN
1

PDN 1
ul/dl data_transfers

I2

GGSN
2

PDN 2

GPRS - CN


43


Page 43

2 GPRS Operation
> User data transfer
SGSN

over the Gi
interface

GGSN
over the Gn interface

@ MS
@server

U-data

@ MS
@server

U-data

MS
U-data
within the MS

@ggsn
@sgsn

UDP
header

@ MS
@server

GTP
header

GTP
header

@server
@ MS

UDP
header

@sgsn
@ggsn

PDN

U-data
server

@server
@ MS

@server
@ MS

U-data


U-data

44

w User data transfer
Data are transferred from header translation, then encapsulation in underlined protocol data unit.
At the GGSN, the IP address of the MS is used to retrieve a PDP context and therefore a TID and the address of the
current SGSN.
At the SGSN, the TID is used to work out the NSAPI and the IMSI (therefore the TLLI). If the MS is ready, no need for
paging because the MS is located to the exact cell.


Page 44

2 GPRS Operation
2.5 Charging
> Charging process
CCBS
FTP

CG
GTP

MS

BSS

SGSN

GPRS

TLLI

GGSN

BACKBONE

Attachment

PDN

G_CDR

M_CDR S_CDR

PDP CONTEXT ACTIVATION AND DATA TRANSFERT


45

w CDR (Call Detail Record)
CDRs are used for subscriber charging, statistics and location purposes.
Three types of CDR are managed within the GPRS backbone:
M-CDR related to the GPRS mobility of a mobile station
S-CDR related to PDP-contexts activation and data transfers as seen by the SGSN
G-CDR related to PDP-contexts activation and data transfers as seen by the GGSN
CDRs, generated by the xGSN, are then sent to the CG (Charging Gateway) :
periodically,
using reliable transfers (GTP over TCP)
The CG forwards those CDRs to external CCBS (Customer Care and Billing System)
w CDR content
Here are the main information in the CDR :
IMSI
location information (LAC + RAC + Cell)
APN
PDP-context identifier
PDP-context start time and duration
negotiated QoS
volume of data sent / received
source and destination PDP addresses,
….


Page 45

2 GPRS Operation
2.5 Charging
> Charging process
VISITED PLMN
TLLI

SGSN

VPLMN
BG

BSS

MS

CG

CCBS

INTER PLMN NETWORK
HOME PLMN

S_CDR

CCBS

BG
HPLMN

CG

GGSN

PDN

G_CDR
46



w Charging data collection for inter-PLMN charging
Use of G_CDR and S-CDR as specified by GSM 12.15
Inter-operator agreement to transfer between Billing Systems


Page 46

2 GPRS Operation
2.6 Security
1- Secured network access
• Authentication of MSs and confidentiality of
their identity
• Possibility of encrypting user data
• Possibility of verifying IMEI with an EIR (Gf)

2- Secured backbone IP network
Firewall = application-level filtering
Filtering by access lists (in the GGSNs)

GPRS Network
Public Internet

3- Secured intranet access
APN with mandatory subscription
APN with access lists
APN with tunneling on Gi (IPsec)

47

w Authentication and confidentiality
As in GSM, by security triplets and the use of the TLLI/P_TMSI instead of the IMSI.
w Encryption
The LLC frame is encrypted, so encryption from the MS to the SGSN and not just on Um.
w Firewall
Filtering function installed on routers (ex: GGSN). Packets are rejected by filtering at application level (for example: in http,
some URLs are barred). Also makes it possible to hide the IP addresses of MSs and backbone entities from external hosts
(Network Address Translation function).
w Access Lists (IP addresses lists)
A function of Cisco routers (and therefore of GGSNs). Each APN is linked to two lists of IP addresses to be checked during
the PDP context activation phase (calling address and called address in both UL and DL directions).
These lists are therefore used to protect access to the operator's backbone IP, but also to filter the access to external
PDNs.
At the GGSN, some APNs can be declared "with mandatory subscription" (at the HLR) and therefore inaccessible to other
MSs.
w Tunneling
Several ways:
by IPsec (Secured IP) = IP version in which the user data is encrypted (IP datagrams payload but not their header).
Or by Generic Routing Encapsulation (GRE)
by PPTP (Point-To-Point Tunneling Protocol). Refer to ANNEX for PPP Tunneling.


Page 47

2 GPRS Operation
Exercise (1/3)
–

True or False?
–

The GGSN reads the header of user packets arriving from the PDN

–

The GPRS HLR knows the location of an MS to the nearest RA

–

With each web page downloaded, a new PDP context must be
activated

–

A CDR is generated for each packet sent or received

–

The SGSN can be considered as PMSC and PVLR

–

A TLLI is a virtual connection between a GPRS attached mobile and the
GGSN

Time allowed :
5 minutes


48

w PMSC: Packet MSC.
w PVLR: Packet VLR.


Page 48

2 GPRS Operation
Exercise (2/3)
–

True or False ?
–

The Charging gateway provides a single interface towards the billing centers

–

No need for paging to send a packet to a mobile in the "Ready" state

–

Attachment to the network does not involve GGSN

Time allowed :
5 minutes

49


Page 49

2 GPRS Operation
Exercise (3/3)
–

What interfaces of the GPRS NSS does a packet cross from a PDN to an MS?

–

Why , theoretically, is an RA smaller than an LA?

Time allowed :
5 minutes

50


Page 50

2 GPRS Operation
Evaluation
> Objective : to be able to describe the
organization of a GPRS network :
architecture, interfaces, protocols,…

the self-assessment

51


Page 51

3

The Base Station Subsystem



Page 52

> Objectives :
• To be able to briefly describe the data
interchange mechanisms through the BSS

> Program :
• 3.1 3GPP Position
• 3.2 Alcatel’s Choice
• 3.3 Layered Model
• 3.4 Gb Interface
• 3.5 Radio Interface


53


Page 53

3.1 3GPP Position
> PCU function
BSS

BTS
CCU

BSC

SGSN

PCU

BTS
CCU

BSC

BSS

SGSN

PCU

BTS

BSC

BSS

PCU

CCU


SGSN

54

w PCU functions
RLC and MAC layers: LLC frame transportation (segmentation/reassembly),
Gb interface end point,
network access functions (radio resource management),
radio channel management (power control, congestion control, etc).
w CCU functions
encoding suited to radio channels,
radio measurements (receive quality, signal level, "timing advance" management).


Page 54

3.2 Alcatel’s Choice
> PCU function

MFS is just the name of the
rack containing PCU functions
Abis

Ater
GSL

BTS

BSC

Gb

MFS

SGSN

PCU

CCU

BSS
LLC Transmission check between SGSN and MS
RLC Transmission check between PCU and MS
GCH transmission check between PCU and TRE


55

w The Multi BSS Fast packet Server (MFS):
w MFS is just the namee of the rack containing PCU functions
performs the GPRS Packet Control Unit (PCU) functions (3GPP 03.60 standard),
manages the Gb interface with the GPRS & EGPRS core network,
performs the Serving Mobile Location Center (SMLC) functions,
manages the SAGI interface with the A-GPS server.


Page 55

3.3 Layered Model
> User plane
IP

SNDCP

SM

GMM SM

GMM

LLC

SNDCP

LLC
PCU

RLC
RLC

MS

Frame
relay

Frame
relay

L2-GCH
L1-GCH

Physical
layer

Physical
layer

relay
Physical L2-GCH
layer
L1-GCH

Um

BTS


BSSGP

BSS
GP

MAC

MAC
Physical
layer

relay

Abis/Ater

MFS

Gb

SGSN

56

w For GPRS TRAFFIC, the BSS simply relays the LLC frames between the MS and the SGSN.
w BSSGP = BSS Gprs Protocol. Functions:
to relay LLC frame over the Gb, with no guarantee of integrity (relaying user data and GMM / SM messages :
session, RA_update and paging procedures). Conceals the FR layers for the LLC layer.
SGSN-MFS signaling = management of Gb interface objects (flush, paging, resume suspend, LLC-discarded and
other procedures).
cell-SGSN traffic management (identified by BssgpVCs): in particular cell update management (in the same RA):
the BSSGP header always indicates the current cell so if a "ready" MS moves into a new cell, then the SGSN
stores this new cell and sends all the unacknowledged LLC_PDUs to it (DL).
w The concept of handover has no meaning in packet switching (GPRS). There is no "circuit" to re-establish!
w RLC = Radio Link Control. (Provides a safe link for transporting LLC-PDUs in acknowledged or unacknowledged mode,
LLC-PDU segmentation into blocks and reassembly, management of TBF contexts. RLC depends on the physical bearer:
data encoding, error control and flow control suited to GSM channels.
w MAC = Medium Access Control. Multiplexing of RLC frames onto PDCH (transfer of blocks over the different PDCHi).
Including traffic sharing over several TSs or, conversely, the use of one TS for several users.


Page 56

3.3 Layered Model
> Signaling plane
BSCGP
BSCGP
L2-GSL
L1-GSL

L2-GSL
L1-GSL

RRM

RRM

relay

relay

physical
layer

physical
layer

MS

Um

BTS

Abis

BSC

Ater

MFS

Gb

57



w BSCGP protocol
administration interface of Radio Resource management :
(de)allocation of PDCH and MPDCH within a cell
activation / release of PDCH
System control information:
BSC reset procedure
cell and GIC group state management
Radio signalling :
GSM / GPRS paging,
GPRS access procedure
w RMM protocol
dynamic allocation of Radio Resources to a MS :
radio blocks from one or several PDCH
for uplink or downlink data transfers


Page 57

3.4 Gb Interface
> Managed entities
BSS side

GPRS Core Network side
BVCI=2
PCM
BC

BVCI=2
BVCI=1
BVCI=3

BSC1

NSVC1

PCM
PVC
BC

BVCI=1
NSE1

NSE1
PCM
BC

NSVC2

PCM
PVC
BC
BVCI=3

F.R
Network
PCM
BC

BVCI=5
BVCI=4
BVCI=6

BSC2

NSVC3

BVCI=5
BVCI=4

PCM
PVC
BC
NSE2

NSE2
PCM
BC

NSVC4

PCM
PVC
BC
BVCI=6
SGSN


58

other procedures).


Page 58

3.4 Gb Interface
> Protocols
BSS side

GPRS Core Network side

BVCI=2
BVCI=1

BSC1

BVCI=3

BSS GPRS Protocol

BSS GPRS Protocol

BVC

(BSSGP)

(BSSGP)

BVCI=5
BVCI=4
BVCI=
6

BSC2

NSE

Network Service Control

Network Service Control

(NSC)

NS-VC

(NSC)

Sub-Network Service

PVC

Sub-Network Service

(SNS)
Physical layer

PCM

Packet Control Unit function
(PCU)

(SNS)

BC
PCM

Physical layer

Frame Relay

SGSN

59

other procedures).


Page 59

3.5 Radio Interface 1/8
> GPRS / EGPRS throughput

EGPRS

Modulation

Maximum rate
per PDCH (kb/s)

CS4
CS3
CS2
CS1

GMSK
GMSK
GMSK
GMSK

21.4
15.6
13.4
9.05

MCS9
MCS8
MCS7
MCS6
MCS5

8-PSK
8-PSK
8-PSK
8-PSK
8-PSK

59.2
54.4
44.8
29.6 / 27.2*
22.4

MCS4
MCS3

GMSK
GMSK

17.6
14.8 / 13.6*

MCS2
MCS1

GPRS

Coding Scheme

GMSK
GMSK

11.2
8.8
* in case of padding


60


Page 60

> Coding schemes
Bad radio condition
Max security

CS1

Good radio condition
Min security

CS2

CS3

Max number of bits for
user data

Maximum number of bits to
have security

BETTER USER BIT RATE

POOR USER BIT RATE


CS4

61


Page 61

> GMSK / 8-PSK modulations
1

1 bit per
Symbol

0

1

1

Gross bit rate
per carrier

GMSK

270 kb/s GMSK
One TS 142 symbols
142 Bits

ONE TS

One TS 142 symbols
426 Bits

ONE TS
001

3 bitS per
Symbol

101

011

001

8-PSK

810 kb/s 8-PSK
8 PSK has 3times more capacity than GMSK


62

w Transmission and reception data flows are the same for GPRS and EGPRS, except for EGPRS MCS-9, MCS-8 and
MCS-7, where 4 normal bursts carry 2 RLC blocks (1 RLC block within 2 bursts for MCS-9 and MCS-8).
w Radio blocks are transported on the air interface (Um) over 4 consecutive normal bursts of the TDMA frame.
w The GMSK normal burst is composed of 156.25 symbols (1 bit for 1 symbol):
6 tail symbols,
26 training sequence symbols,
114 encrypted symbols,
2 stealing flags (2 symbols),
8.25 guard period (symbols).
For GMSK, the radio blocks are transported by 114 x 4 = 456 symbols.
w The 8-PSK normal burst is composed of 156.25 symbols (3 bits for 1 symbol):
6 tail symbols,
26 training sequence symbols,
116 encrypted symbols (there is stealing flags),
8.25 guard period (symbols).
For 8-PSK, the radio blocks are transported by 116 x 4 = 456 symbols.


Page 62

> Transmission Rate with 8 PSK modulation
CHANNEL

Bad radio condition

Good radio condition

MCS9
MCS8
MCS7
MCS6

MCS1
8,8k

MCS2 MCS3
11,2k

MCS4

14,8k

17,6k

MCS5

22,4k

29,6k

Maximum number of bits to have security

44,8k

54,4k

59,2k

Max number of bits for user data
63



Page 63

> Impact of EGPRS (Edge) on terrestrial transmissions in BSS

CS1 about 9K
PDCH

BTS

TRX

GMSk and Not a
good transmission

BSC

16k resource

relay

Abis

MFS

16k resource

PCU

Ater

MCS9 ABOUT 59K
BTS

PDCH

TRX

BSC

Extra capacity

relay

MFS

Extra capacity
Extra capacity

Extra capacity

8PSK good
transmission

Extra capacity

Extra capacity

Extra capacity

PCU

Extra capacity


64


Page 64

> Resources allocation according to the MCS
MCS n
PDCH

BTS

TRX

Extra capacity

BSC

Extra capacity

relay

Extra capacity

Extra capacity

Extra capacity

MFS

PCU

Extra capacity

QUALITY OF TRANSMISSION LOT OF BITS LOST
INCREASE SECURITY DECREASE USEFUL TRANSMISSION RATE

PDCH
BTS

TRX

Extra capacity

BSC

Extra capacity

relay

Extra capacity

Extra capacity

Extra capacity

MFS

PCU

Extra capacity

MCS n-1
Can be allocated to
another PDCH

Can be allocated to
other PDCH

65

w When the operator decide that the TRX will run MCS n all the terrestrial resources will be allocated , but if the quality of
the radio transmission is bad the PCU decides to increase the security on the air interface, the useful transmission rate on
the PDCH will be decreased and less capacity will be needed on the terrestrial transmission .
w The resource which is not used a that time can be allocated to another TRX if needed at BTS level
w The RLC blocks coming from different are multiplexed on the common resource for all the PDCH in the TRX which is
called M EGCH (Multiplexed EGCH)


Page 65

3.5 Radio interface 7/8
> UL transfer

TBF

start
of TBF1

MS

end of
TBF1

TBF2

MAC

network

TBF3

TBF4

fULi

time
Packet Channel Request
Packet Resource Assignment
(list of PDCHi, token=T,TFIk)

PCU

MS starts listening to all DL blocks token value on the allocated PDCHi
DL PDCHi

N

Ø

Ø

T

T

Ø

T

Ø

T

T

T

Ø

TFIk

TFIk

Ø

TFIk

Ø

TFIk

TFIk

TFIk

in block b
token =T ?
Y

SEND on block b+1 (TFIk)

UL PDCHi

?

Ø

Ø


66

w This slide demonstrate that the radio resources (blocks) are used only when data need to be transferred (LLC-PDU) :
dynamic radio resource allocation. As a matter of fact, an MS shall specify its radio resource request at initiation of each
TBF for a better optimization of radio resource & MS capabilities.
w A TBF (the blue shape) comprises one or more consecutive LLC-PDUs.
w Temporary (Block) Flow Identity = TLLI + sequential number, used by the network to recognize data from different MSs.
Identifies uniquely a TBF in one direction within a cell.
The blocks are dynamically allocated upon the use of a token (Uplink State Flag) allocated to the MS at TBF
establishment. Any DL block includes a USF in the header.
The mobile "listens" to the PDCHi assigned, when block b (in DL) contains USF = T, the MS shall send one
PDTCH in UL on block b+1 on the UL PDCHi.
w The theoretical maximum of 160 kbit/s is given for one MS which would have 8 PDCHs of 21.4 kbit/s each. Those MS are
yet to be available on the market place.


Page 66

3.5 Radio interface 8/8
> DL transfer

PCU

SGSN
PS Paging

Paging Request ("packet")

MS PDU

MS IN STANB BY
MODE

Packet Paging Response

UL TBF: refer to
previous slide

MS IN READY
MODE

Packet Resource Assignment
(list (PDCHj),TFIz)

MS starts listening to all DL blocks TFI value on the allocated PDCHj

DL PDCHj

Ø

Ø

Z

Z

Ø

Z

Ø

Z

Z

N
in block b, TFI=TFIz ?
Y

The MS consumes the content of block b

67

w In DL, each time an LLC-PDU is received, if there is no TBF in progress, it is essential to “establish" one.
w To respond to the paging, the MS needs to send a "paging response" to the SGSN (GMM) encapsulated in an LLC_PDU.
This response is carried by an UL TBF.
w Upon reception of the Paging response, the SGSN can send the DL PDU (LLC frame) to the MS through the MFS.
The MFS shall establish a DL TBF with the MS.
w DL TBF: each block of the DL TBF are identified by the DL TFI = TFIz
w After completion of the TBF establishment phase, the MS listen to all the DL blocks on the allocated PDCHs and keeps the
blocks tagged with the TFIz.


Page 67

Exercise (1/2)
–

True or False?
–

–

For each cell, the number of channels which can be
used for GPRS traffic is operator-configurable

–

If a user packet is lost at the Gb interface, it can be
recovered using frame relay protocol mechanisms

–

Time allowed :

The SGSN is linked to the BSS by an interface based on
the Frame Relay protocol

The LLC protocol is independent of the type of BSS
employed

5 minutes


68


Page 68

Exercise (2/2)
–

True or False?
–

In a cell, a TRX can carry eight PDCHs

–

One PDCH can be allocated in its entirety to a single user

–

If necessary, blocks on different PDCHs can be allocated to a
single user

–

The NSEI is the identifier used by the SGSN to indicate the
destination cell of a LLC frame to the MFS

–
Time allowed :The same quantity of PVCs is declared on the MFS and SGSN

5 minutes

sides


69


Page 69

Evaluation
> Objective : To be able to briefly describe
the data interchange mechanisms through
the BSS

the self-assessment


70


Page 70

4

Alcatel Solution



Page 71

4 Alcatel Solution
> Objectives: to be able to characterize the solution
offered by Alcatel
> Program:
• 4.1 GPRS Network Overview
• 4.2 Alcatel 9135 MFS
• 4.3 Packet Switched Core Network
• 4.4 GPRS Network Management
• 4.5 Alcatel QoS Offer


72


Page 72

4 Alcatel Solution
4.1 GPRS Network Overview
Radio subsystem
B
T
S

GSM/GPRS common servers

BSS1
MSC

HLR

CAMEL & IP based
Prepaid
SCP Services

SMS-C

BSC

B
T
S

GPRS Core Network
A9135
MFS

BSS2

B
T
S

SGSN
Intranet

BSC
GPRS IP
backbone

Frame
Relay
network

B
T
S

Firewall
iGGSN

access
router
Internet

BSS--

B
T
S

SGSN

BSC

Charging Gateway

A9135
MFS

B
T
S

Border
Gateway

Inter-PLMN
backbone

OMC-CN
73



w Within the radio subsystem :
Existing Alcatel BTS and BSC from GSM are reused for GPRS :
no need of hardware change to provide GPRS features
need just software upgrade
The GSM-BSS now includes a proprietary equipment :
Alcatel A9135 = MFS (Multi BSS Fast packet Server)
which deals with the GPRS PCU functions
w

Within the GPRS Core Network :
both SGSN and iGGSN are Alcatel proprietary equipments
Charging Gateway and OMC-CN are Alcatel components based on HP platform
Firewalls, Border gateway and access routers are standard IT components

w The HLR, MSC, SCP and SMS-C are reused from the GSM-NSS


Page 73

4 Alcatel Solution
> Functional architecture
Control Subsystem

OMC-R

M
F
S

LAN x 2

A-ter if
B
T
S

Gb if

BSC1

GPU1
PCU

B
T
S

S

GPU2
PCU

G
Telecom Subsystem

B
T
S

S

GPU1

BSC2

PCU

B
T
S

GPU1

N

PCU

74



w The duplex "Control subsystem" (two DS10 in active/standby mode, with 2 shared disks) :
controls the “telecom subsystem” (initialization, supervision, defence)
provides the management interface (OMC-R or local maintenance terminal)
w The “Telecom subsystem” is composed of GPU boards :
1.

GPRS Processing Unit (GPU).

2.

Each GPU board performs the PCU functions towards the BSC and the SGSN
16 PCM ports per GPU board
some PCM ports connected to the BSS, the other to the SGSN

w There are two different configurations regarding the support of BSC by the GPU boards :
only one GPU board supporting each BSC (in the B6.2 release)
multiple GPU boards supporting each BSC (from the B7 release)


Page 74

4 Alcatel Solution
4.2 Alcatel 9135 MFS CONNECTIONS
120 CICs

TC SM

BSC

MSC
BSC

BSC

120 GICs 16K

A Interf
PVC
PCU

BSC

PCU

FRAME

PCU

SGSN

RELAY

PCU

PMSC
PVLR

BSC
PCU

MFS

Muxed ATer

75

Gb
BEARER CHANNEL



Page 75

4 Alcatel Solution
> Rack layout
1 BSXTU
1 BSXTU
11 GPU (+1)
11 GPU (+1)
maxi
maxi

1 BSXTU
1 BSXTU
11 GPU (+1)
11 GPU (+1)
maxi
maxi

2 DS 10
2 DS 10
Control
Control
sub-rack
sub-rack

2 or 4
2 or 4
Switches
Switches
3 COM 3300
3 COM 3300
+ IOLAN module
+ IOLAN module

76

w The "Control sub-rack" part is duplex (two DS10 in active/standby modes).
w each BSXTU sub-rack contains a maximum of 12 JBGPU boards.
The GPRS traffic of one BSC can be handled by several GPUs (up to six are foreseen from the same MFS rack)
Since B7, a full MFS contains from 4 to 22 BSS (BSC), due to multi-GPU feature
4 BSS per MFS: 2* (1 BSS / 6 GPU)+(1 BSS / 5 GPU)
22 BSS per MFS: 22*(1 BSS/GPU)
w One JBGPU board (= 1 PCU) offers 480 PDCH. Two uses of JBGPUs :
1.

One JBGPU for each BSC, (Ater interface), so one MFS serves a maximum of 22 BSCs.

2.

With 240 PDCH per GPU, a BSC can offer up to 6*240 = 1440 PDCH

3.

To be connected to the FR network (Gb interface).

w Fast ethernet Switches (100 Mb/s) made by 3COM: 2 or 4 (as needed) to build LANs to which are connected
the Nectar stations (DS10)
GPU boards
printers and craft terminals (for local management, the terminal is called IMT = Installation & Maintenance
Terminal)


Page 76

4 Alcatel Solution
4.2 Alcatel 9130 MFS (1/3)

ATCA
shelf

ATCA
shelf


77

w This platform is a high availability distributed platform composed of blades compliant with the Advanced Telecom
Computing Architecture (ATCA) open standard
w ATCA has been developed by the PCI Industrial Computers Manufacturers Group (PICMG).
w The related specifications are described in the PICMG 3.0 R1.0.


Page 77

4 Alcatel Solution
4.2 Alcatel 9130 MFS (2/3)
General

Option 1

Option 2
ATCA shelf content

MFS

ATCA
shelf

G
P

MFS

MFS

LIU

G
P

G
P

G
P

O

S

S

O

M

S

S

M

C

ATCA
shelf

G
P

W

W

G
P

G
P

G
P

G
P

G
P

C

LIU


P

P

78

w LIU: Line Interface Unit – to collect the external PCM connections
w GP: GPRS Processing module
w OMCP: O&M Control Processing board – the control stations,
w SSW: Subrack SWitch


Page 78

4 Alcatel Solution
4.2 Alcatel 9130 MFS (3/3)
E1 connections
Abis

L
I
U

16 LIU X 16 E1

Ater

M
M
U
UX
X

L
I
U

S
S
S
S
W
W

GP
GP
GP
GP
GP
GP
GP
GP
GP
GP

MFS

9 PCU + 1SPARE

OMCP
OMCP

79



w LIU shelf: Multiplexes/demultiplexes and cross connects all E1 external links to/from NE multiplexed links (n E1 over
Ethernet) on the TP and the GP board. Equipped with two Mux boards and n LIU boards, depending on capacity.
w The LIU shelf hosts Two MUX boards which collect the E1 links from the 16 LIU boards on 16 serial links at 36.864 Mbit/s
and build packets sent towards up to 32 directions (125ms each) on a Gigabit Ethernet link.
w SSW: it’s an Ethernet switch which allows exchanges between all platform elements and externalIP/Ethernet equipment.
w OMCP: these control stations are used to process defense functions and platform Operation, Administration and
Maintenance (OAM) generic services..
w GP: Manages the user plane packet data flow processing.
w Ethernet links on the IP ports of the SSW switch: these links connect the platform to external IP equipment (i.e. OMC-R,
external alarm box).


Page 79

4 Alcatel Solution
towards Prepaid Servers

> SGSN

> iGGSN

Pilot Blades

O&M, Charging

GPRS
signaling & user
Plane Blades

O&M & service
provisioning

Intra-PLMN
DNS

SS7 Blades

Vigilon

Gr, Gs,

Senteon

session control
logic

Gd, Ge

PDN1

GPRS IP
Backbone
WN

Gb

WN
GPU

PDN2

Ethernet LAN (internal com.)
Switching & Routing

OMC-CN

Charging
Gateway

GTP control &
user planes

80



w The SGSN is ATCA based component (Advanced Telecom Computing Architecture). The main functions are distributed
over different hardware modules :
SS7 network interfaces (Gs, Gr, Gd) by a number of ATCA SS7 blades,
Gb interface by a number of Alcatel proprietary GPU boards,
SGSN O&M and GPRS charging agent (initialisation, defense, O&M, and CDR) by a cluster of ATCA Pilot blades,
GPRS signaling and user traffic handling by a number of ATCA control & user plane blades
SGSN internal communication, switching and routing of user traffic by a dedicated Ethernet switch
w The iGGSN is an Alcatel proprietary equipment, where the main functions are distributed over 3 hardware modules :
Vigilon server for iGGSN O&M, subscriber configuration and service provisioning,
Senteon server as a control logic for subscription and credit check during session establishment phase,
WN1200 node for full 3GPP GTP services


Page 80

4 Alcatel Solution
SGSN rack

backbone rack

iGGSN rack

NTS150
NTS150

GPU boards

NTP Servers
Gn switches

NS500

Ethernet
switch/routers

WN1200

NS500

Firewalls

border router

ATCA platform
pilot blades

access router
Senteon 1&2

GPRS control
& user plane
blades

external DNS
Ethernet
switch/routers

SS7 blades
Internal control LAN


Intra-PLMN
DNS/DHCP

81


Page 81

4 Alcatel Solution
4.4 GPRS Network Management
> Dedicated OMCs
BSC1

B
T
S
B
T
S

Radio part
BSC2

B
T
S

OMCR
MFS

NMC
Q3

SGSN

Core Network part
OMCCN

DNS/DHCP

NTP

BG

iGGSN

Charging
Gateway

82



w OMC-R: Called Alcatel 1353 RA = management of the radio subsystem :
Alcatel 9135 MFS.
BSCs and associated BTSs
w OMC-CN : called ALMA 1364 GPRS = management of the Core Network :
the SGSN server
the SGSN router
the GGSN.
The Charging Gateway (alarm supervision)
the DNS/DHCP server (supervision)
the GPRS network level (APN and Routing Areas)


Page 82

4 Alcatel Solution
> R97/98 QoS compliance
ETSI R’97/98 QoS attributes
Delay class

Mean throughput
class

Precedence class

Alcatel Offer
Resulting QoS class

(4) Best Effort

any

any

Best-Effort

1, 2 or 3

(3) Low priority

any

Best-Effort

1, 2 or 3

Normal, High priority

Best Effort

Best-Effort

1, 2 or 3

(2) Normal priority

specified, except BE

Normal

1, 2 or 3

(1) High priority

specified, except BE

Premium

as required by the MS

Reliability class:

83



w These QoS attributes are associated with a PDP context performed by a R97/98 MS
w The five QoS parameters of the standard define more than 60 combinations ! Which is too much and leeds to simplification
:
Too complex to implement,
Many of the combinations have no meaning!
The standard "allows" more simple QoS implementations.
“-” = any value.
In bold, the main criterion for definition of the resulting QoS.
w Best effort = inexpensive, comparable to the Internet (no commitment). Ideal for foraging on the internet.
w Normal:

Comparable to an intranet.

w Premium:

Expensive, high performance.


Page 83

4 Alcatel Solution
> R97/98 QoS mapping into R99 QoS

R99 Traffic class

Traffic handling priority

conversational

R97/98 Bearer QoS class

-

Premium

streaming

-

Premium

interactive

1

Premium

interactive

2

Normal

interactive

3

Normal

background

-

Best Effort


84

w The mapping of R97/98 QoS attributes to R99 QoS is applicable in the following cases :
hand-over of PDP context from GPRS R97/R98 SGSN to GPRS R99 or UMTS SGSN
when a R99 MS performs a PDP context activation in a R99 SGSN with a R97/98 GGSN
when the SGSN has received R97/98 QoS subscribed profile, but the MS is R99
w The mapping of R99 QoS attributes to R97/98 QoS is applicable in the following cases :
PDP context is handed-over from GPRS R99 to R97/R98
when a R99 MS performs a PDP context activation in a R99 SGSN while the GGSN is R97/98
when the SGSN sends user data to the BSS for a R99 MS
when the SGSN has received R99 QoS subscribed profile but the MS is R97/98
in the new SGSN, during an inter-SGSN RA_update procedure, or inter-system change, on receipt of the R99 QoS
attributes from the old SGSN


Page 84

4 Alcatel Solution
Exercise (1/2)
–

True or False?
–

–

The iGGSN is an Alcatel proprietary
equipment

–

The SGSN server is an Alcatel proprietary
equipment based on IT devices

–

Time allowed :

Implementing GPRS in the BSS simply entails
adding A9135 or A9130 MFS servers

The DNS/DHCP servers used in the GPRS
Core Network are IT standard servers

5 minutes


85


Page 85

4 Alcatel Solution
Exercise (2/2)
–

True or False?
–

GPRS Core Network equipments are managed from an
OMC- CN

–

GPRS radio subsystem (BSS) equipments are managed
from an OMC-R

–

Alcatel GPRS network handles simultaneously the UMTS
QoS classes (R99 QoS parameters) and the GPRS QoS
profiles (R97/98 QoS attributes)

Time allowed :
5 minutes


86


Page 86

4 Alcatel Solution
Evaluation
> Objective : to be able to characterize the
solution offered by Alcatel

the self-assessment


87


Page 87

5

Annex and Glossary



Page 88

5 Annex 1
Coding Schemes : CS1 -> CS4

Channel rate (kbps)

20

CS4
CS3

15

CS2
10

CS1

5
0
0

10

20

30

C/I (dBm)

BACK

89



w The data rate on a PDCH depends on the coding scheme :
for CS-1: PDCH data rate = 9.05 kbit/s (poor radio conditions or BSS signaling)
for CS-2: PDCH data rate = 13.4 kbit/s (better radio conditions)
for CS-3: PDCH data rate = 15.6 kbit/s
for CS-4: PDCH data rate = 21.4 kbit/s.
w The system selects automatically the best coding scheme :
the data rate is set according to the current C/l.
maximum data rate (160 kbit/s) only possible with CS4 on 8 parallel channels


Page 89

5 Annex 2
GPRS compared to other technologies

2 Mbps

Bit rate

384 Kbps
160 Kbps
64 Kbps
9.6 Kbps
Technology
CS data - SMS, 9.6Kbps
HSCSD
GPRS
EDGE
UMTS

90

w SMS : With GPRS, the 160-character barrier for short messages will be able to be broken (when SMS over GPRS is
implemented).
w High Speed Circuit-Switched Data : This still involves circuit switching, meaning that, with a continuous use of radio
resources, so billed by time. HSCSD is based on the assignment of several traffic channels (TCH) to a single MS to offer a
higher bit rate. HSCSD is suited for services requiring a minimum bandwidth guaranteed.
w EDGE : (Enhanced data rates for GSM evolution) is a technology previously developed by Ericsson, based on TDMA and
offering a maximum theoretical speed of 384 kbit/s (8 channels, each 48 kbit/s, using a new modulation scheme: 8-PSK,
eight-phase shift keying, instead of GMSK for GSM and GPRS).
w EDGE-specific MTs are required! The BSS remains the same, except for the implementation of EDGE TRX (Evolium
product line).
Alcatel will offer EDGE from release B8 onwards. This is an important step towards UMTS
w UMTS : requires a new Radio Access Network based on W-CDMA technology.
The UMTS standard is part of the Third Generation (3G). Together with CDMA 2000 and other systems, they form a set of
ITU radio access technologies standardized by IMT 2000.


Page 90

5 Annex 3
PCU concept
PCU JBGPU FUNCTION
TBF = Temporary Block Flow

TFI 9

TBF
9

1

9

TFI = Temporary Flow Identifier BSN = Block Sequence Number

TBF from SERVER 9

2

9

TBF

4

9

4

9

5

9

6

21

22

TBF

7

TBF from SERVER 4

2

4

23

4

24

4

25

4

26

4

27

4

TFI 2

2

90

89

2

91

90

28

4

29

4

30

4

31

TBF from SERVER 2
2

92

2

93

2

94

2

95

TS x dedicated to ONE PDCH
2

9

TFI 4

4

3

4

21

4

22

9

1


2

2

96

2

97

2

98

2

99

2

10

one PDCH shared by N users
91

2

92

9

2

4

23

2

93

2

94

91


Page 91

4

2

5 Annex 4
PCU concept
LLC Checks the transmission between SGSN and MS
RLC checks the trans between PCU and MS
PDCH

PCU

TRE /BTS

CCU
Gb

n RLC
blocks
RLC blocks
- token
- Data
- radio security


LLC blocks

92


Page 92

5 Annex 5
TDMA and PDCH
> TDMA frame and GPRS physical channels
8Psk 171
0

1

2

3

4

5

6

7

FRAME 0

4

4

0

57

171
1

2

3

4

5

6

7

FRAME 1

4

4

4

4

4

4

4

4

4

Gmsk

57
0

1

2

3

4

5

6

7

4

4

4

4

4

4

4

1

2

3

4

5

6

7

FRAME 3

FRAME 2

4

0

4

4

4

4

4

4

4

4

F00 F01 F02 F03 F04 F05 F06 F07 F08 F09 F10 F11 F12 F13 F14 F15 F16 F17 F18 F19 F20 F21 F22 F23 F24 F25

4

F50 F51

PTCCH
B0

B1

B2

B3

B4

B5

B6

B7

B8

B9

B10

B11

1 PDCH
12 BLOCS
Frame
12

52 FRAMES then 52 TS x and 240 ms

Frame
38

BLOC 3


93


Page 93

5 Annex 6
GPRS channels
> Master and Slave PDCHs
MASTER PDCH

PDCH
DOWN/UPLINK

B1
B2
B3
All blocs can
be used as
- PDTCH
- PACCH

B1

B4
B5
B6
B7
B8

B2

B9
B10
B11

Blocs which
can be used
as
- PAGCH
- PDTCH
- PACCH
Blocs which
can be used
as
- PPCH
- PAGCH
- PDTCH
- PACCH

/UPLINK

B0

B0

B1

B1
B2

B3

B3

B4

B4

B5

B5

B6

B6

B7

B0

Blocs which
can be used
as
- PBCCH

DOWN

B2

B0

B7

B8

B8

B9

B9

B10

B10

B11

B11

All blocs can
be used as
- PRACH
- PDTCH
- PACCH

94



w For each cell, it is possible to define the MINIMUM and MAXIMUM number of channels reserved for GPRS + the maximum
number of channels reserved for GPRS in case of high traffic load (when the BSC sends "Load indication" to the MFS
through BSCGP protocol).
w There are two types of PDCH : MPDCH and SPDCH
MPDCH = Master PDCH = PBCCH + PCCCH (PPCH + PAGCH + PRACH) -> carries GPRS signaling and system
information.
SPDCH = Slave PDCH -> carries the user traffic.
w Benefits of the Master Channel :
Preserves CCCH capacity for speech services
Higher GPRS signaling capacity, in line with GPRS traffic growth
Differentiated cell re-selection strategy between GPRS and non GPRS MS. When GPRS attached, a MS listen to
PSI broadcast on PBCCH. It allows a finer tuning of GPRS re-selection algorithms, for example in hierarchical
networks (C31 and C32 criteria). Otherwise, MS applies the basic Cell-reselection as in GSM Idle-Mode using the
C1 and C2 GSM criteria


Page 94

5 Annex 7
PDCH ,TBF, MAC concepts
TFI 1
TFI 5
TFI 3
TFI 6

TBF from server 1
TBF from server 2
TBF from server 3
TBF from server 4
B1

DOWN
u3

B2
u3

UP
TFI 2 USER 3
TFI 7 USER 6
TFI 6 USER 2

B3
u3

B2

B4
u3

B3

B5
u3

B4

B6

B7

u3

B5

u3

B6

B8
u3

B7

B9
u6

B8

B10
u6

B9

B11
u2

B10

B12
u2

B11

B1
un

B12

B1

TBF server 5
TBF to server 6
TBF to server 7


95


Page 95

5 Annex 8
Different uses for E1
> PCM E1 and Bearer Channel uses and concepts
BEARER CHANNEL=960K
TS 1

2

TS 2

64K

M
B

TS 3

64K

TS 4

64K

TS 5

TS 1

16K X 4

2

TS 2

32K X 2

2

M
B

TS 3

64K X 1

M
B

64K

64K

64K

TS 4
128K 64K X 2

TS 1
TS 2
TS 3
TS 4

TS 15

TS 5

E

TS 28 64K

E

1

TS 29 64K
TS 3

1

TS 31 64K

E

TS 28
TS 29 192K
TS 3

64K X 3

TS 17
TS 18
TS 19
TS 20

1
TS 31

TS 31

BEARER CHANNEL =960K

96

w Minimum size for a bearer channel: 1 x 64k, Maximum size for a bearer channel: 31 x 64k.
w One PVC per bearer channel.


Page 96

5 Annex 9
FRAME RELAY and PVC concepts

DLCI Number
9

PVC y

FRAME RELAY
SGSN

Node
27

PCU

6

MFS

16
15

5

PVCn

12


97


Page 97

5 Annex 10
PVC and NSVC concepts

NSVC Transmission check end to end

FRAME

PCU
MFS

SGSN

RELAY

PCM E1

BEARER
CHANNEL

Permanent Virtual
Connection


98


Page 98

5 Annex 11PCM 1
TDMA and PDCH
BC 1
BC 2

P
C

PCM 1

U

PVC / NSVC
PVC / NSVC

There is One PVC/NSVC per Bearer Channel
BC 3
BC1

PVC / NSVC
NSE NSEIx

PCM 2

There is one NSE for all the PVC of one PCU

99


Page 99

5 Annex 12
Network Mode of Operation I with Master Channel
CCCH

MSC
VLR
A

PCCCH

Gs

BSC

(a)
PACCH

SGSN
(b)

Um

Gb

CS paging for GPRS-attached MS in idle state (a), or in data transfer state (b)
CS paging for non GPRS-attached MS


GPRS paging

100

w In this mode, the Gs interface is present in the core network. As far as GPRS-attached MS are concerned, the BSS
receives both GPRS and circuit-switched paging messages from the Gb interface.
w There is paging co-ordination because all paging messages towards GPRS-attached mobile stations are sent either on the
Master Channel, if present, or on the CCCH otherwise.
w In addition, whilst involved in a packet data transfer the GPRS mobiles receive the circuit-switched paging messages via
the GPRS traffic channel currently used.
w NMO II :
There is neither Gs interface nor Master Channel. There Paging coordination over the CCCH of GSM. Also, GPRS
Mobile Stations operating in Class B may lose CS Paging message if they are not able to monitor CCCH at the
same time.
w NMO III:
In this mode, there is no Paging coordination because Gs interface is not present while the Master Channel is.
Therefore, CS Paging is transmitted over CCCH when PS Paging is transmitted over PCCCH. Class C Mobile are
not able to manage both type of channels.


Page 100

5 Annex 13
MOBILE ONE PHASE ACCESS ON PCCH (Master PDCH)
NETWORK
Packet channel request PRACH
Packet UL assignment + polling
indication PAGCH

TFI
PDCH
USF
TA

Packet Control ACK PACCH

Usf Scheduling

RLC data bloc

PDTCH

Packet UL ACK NACK

PACCH

101



w "Attach" the MS switches on (GMM protocol):
MS sends his previous P_TMSI, otherwise a random one. The attach_request message is placed in an LLC frame
with its old TLLI if its exists, or a randomly chosen TLLI if not.
w TLLI: This is allocated to the subscriber on his attachment to the network. In reality, the SGSN allocates the MS a P-TMSI,
from which the MS and the SGSN itself derive the TLLI.
w The functions of the HLR:
to supply the security triplets
to check roaming restrictions (or ODB)
to store the address of the current SGSN
to initiate the deletion of data from the old SGSN
to send subscriber data to the SGSN
w "Detach" proceeds as follow:
MS to SGSN: Detach request
SGSN to GGSN: Delete PDP context then Acknowledge
SGSN to MS: detach accept


Page 101

5 Annex 14
MOBILE ONE PHASE ACCESS ON CCCH (no master PDCH)
NETWORK
Channel request RACH
Immediate assignment

AGCH
TFI PDCH USF TA

Packet uplink assignment + polling
indication PACCH
Packet control ACK PACCH

TFI PDCH USF

Usf Scheduling

RLC data bloc

PDTCH

Packet UL ACK NACK

PACCH

102





Page 102

5 Annex 15
MOBILE ORIGINATING DATA TRANSFERT
SGSN

BSS
UL TBF
Establishment

Paquet channel request
Paquet UL assignement

STAND BY

RLC PDU
RLC PDU
RLC PDU
PACKET UPLINK ACK/NACK

UL UNIDATA

RLC PDU

READY

RLC PDU
RLC PDU
PACKET DOWNLINK ASSIGNEMENT

UL UNIDATA
UL TBF
Release
103





Page 103

5 Annex 16
MOBILE TERMINATING DATA TRANSFERT
SGSN

BSS

STAND BY

PAGING PS
Packet Paging Request
channel request

UL TBF

Paquet UL assignement
LLC PDU

UL UNIDATA
READY

DL UNIDATA
DL TBF

PACKET DOWNLINK ASSIGNEMENT

104





Page 104

5 Annex 17
GMM - Combined GPRS and NSS attach with Gs (1)
SGSN
Attach_request (IMSI)

HLR

Triplet request ( rand kc sres )

Authentication

Update_location
IMSI ↔ current SGSN

Insert_subscriber_data

Update_location_ack
IMSI ↔ TLLI + current RA + subscription data

Attach_accept (TLLI)
MS ↔ TLLI
TLLI Established

105





Page 105

5 Annex 18
GMM - Combined GPRS and NSS attach with Gs (2)
MSC/VLR

SGSN

HLR

Location_Update_req (IMSI, LAI)
Update_ location (IMSI, @VLR)
IMSI ↔ current VLR
Insert_subscriber_data
Update_location_ack
Location_Update_accept


106

w Location-Update-request: The SGSN determines the MSC/VLR based on the RA where the subscriber is located.
w At the HLR: If the MS was declared in another MSC, the HLR sends it a Cancel_Location before doing ISD to the new
MSC.
w Attach-accept: In practice, the SGSN sends the MS the P-TMSI (and not the TLLI) and the V-TMSI (TMSI of the VLR),
designated TMSI here.
w Once this combined-attach is done, the MS can make combined LA/RA update procedures (see GSM 03.60)..


Page 106

5 Annex 19
GMM - RA update Inter-SGSN (1)
new
SGSN

old
SGSN

GGSN

Routing_Area_update_req (RA1)
SGSN_context_req (RA1, TLLI, @SGSN2)
SGSN_context_resp (MM_ctxt, PDP_ctxt)
SGSN_context_ack
transfer of stored packets
Update_PDP_context_req (TID, @SGSN2)
Update_PDP _context_resp

107

w RA1: This is the mobile's previous RA
The New SGSN retrieves the IP address of the old SGSN from RA1, after request to the DNS which translate RA1 into IP
@ of SGSN1.
w SGSN_context_req:To obtain any PDP contexts and the MM contexts (IMSI, RA, cell, IMEI, etc) = all the data stored in the
old SGSN concerning the MS, including the address of the GGSN related to each PDP context activated.
w SGSN_ctxt _ack: This message is sent only if the subscriber has PDP contexts activated. Used to inform the old SGSN
that receives and stores datagrams for the MS.
w Update_PDP_context_req: Mainly to inform the GGSN of the address of the new current SGSN for this MS. Thus, any new
packet arriving from the PDP network is routed to the new SGSN.
This operation is carried out in parallel with the retrieval of the old SGSN packets, and not afterwards as the figure above
seems to indicate.


Page 107

5 Annex 20
GMM - RA update Inter-SGSN (2)
new
SGSN

old
SGSN

HLR

Update_location (IMSI, @SGSN2)
cancel_location (IMSI)
cancel_location_ack
insert_subscriber_data (+ack)
Update_location_ack
Routing_Area_update_accept (TLLI)
Routing_Area_update_complete


108

w ISD: = ISD (IMSI, GPRS subscription data).
w The tunnel (SGSN-GGSN) moves with the subscriber: The GGSN is always the same and the SGSN is variable (same
TID).
w RA update accept: The SGSN allocates the subscriber a P-TMSI or TLLI, as mentioned (derived from the P-TMSI).


Page 108

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