GPRS - Mipaper by lcis.com.tw

Transcripción

GPRS:
GPRS: System
System Overview
Overview
1
The abbreviation GPRS stands for General Packet Radio Service and the
purpose of this presentation is to provide a comprehensive overview of the
GPRS System. To reach this purpose, the presentation is divided into three
main sections :
• The first one gives an overview of the data services evolution, analizes the
reasons of the GPRS system appearance and shows the GPRS logical
architecture, explaining the role of each component in the GPRS system and
the way that they interchange with.
• In the second one, we will see how a GPRS mobile station registers with a
data network, the problematic that surges when a mobile station applies for
one IP address to exchange data packets with external networks, the solution
of this problem and basic scenarios of roaming.
• Finally, the last section is an overview of the GPRS network security, the
new GPRS billing system and a brief introduction to the evolution to
UMTS.
1
Introducción
Introducción
Evolución
Evolución de
de los
los servicios
servicios de
de datos
datos
2
Every 4 or 5 years we start a new age, so if we go back fifteen or twenty
years, we can see that we have passed the information age, the
communication age, the know- how age, the global economy age and of
course the Internet age. The nearest future is a combination of the
previously mentioned items and which is more important, all of that in a
time-span and space available, thanks to the mobile phone, which is
nowadays essential in our lives.
In less than 2 years, we have got accustomed to use short messages, we have
introduced mobile application support technologies, such as WAP, in our
lives and we already know that UMTS is the next advent of mobile data
services in the third-generation wireless communications.
We must take into account that the authentic progress comes from the
cellular wireless data services, so we should realize that we have entered in
a new period of time known as the wireless communication age and GPRS
is playing an important role in it.
2
GPRS
GPRS -- Introducción:
Introducción: General
General
?
?
?
?
?
?
Cada 4 ó 5 años anuncian una nueva era.
Actualmente estamos inmersos en una nueva era de
verdad: la era de la comunicación inalámbrica (wireless).
Futuro = información + comunicación + conocimiento +
economía global + Internet.
Se busca una disponibilidad total en el tiempo y en el
espacio ? teléfono móvil.
Progreso = tx de datos + movilidad.
Evolución: SMSs ? WAP ? GPRS ? UMTS.
3
3
GPRS
General
?
?
SMS a 9.6 kbps.
WAP está aquí.
? Móvil GSM con browser.
? WAP 1.1 no es seguro.
? WAP 1.2 introduce seguridad (ej. PKIs).
? WAP 1.3 añade más seguridad.
?
?
GPRS ? 80kbps hoy y previsi ón de 100kbps.
UMTS hasta 2Mb (¿quizá en 2002?).
4
4
GPRS
General
?
?
?
?
Crecimiento exponencial de la Telefonía móvil y nº de
usuarios de Internet desde 1995 ? nuevo mercado.
Movilidad esencial en la tx de datos: cualquier lugar.
Carencias en GSM ? Demanda de nuevos servicios de
datos sobre redes móviles (GSM).
Limitaciones de GSM actual: servicios de datos basados en
conmutación de circuitos.
5
The impressive growth of cellular mobile telephone as well as the number
of Internet users promises an exciting potential for a new market of cellular
wireless data services that combines both innovations. Within the next few
years, there will be an extensive demand for wireless data services, because
time span and space availability have become essential in data transmission.
New data services are demanded, but GSM suffers from several limitations
and that is the reason why current GSM (Global System for Mobile
communication) data services, do not fulfil the needs of users and providers.
From the user’s point of view, data rates are too slow, the connection set- up
takes too long and the service is too expensive. From the technical point of
view, the drawback results from the fact that current wireless data services
are based on circuit switched radio transmission. This means that at the air
interface, a complete traffic channel is allocated for a single user for the
entire call period and this results in highly inefficient resource utilization in
case of bursty traffic (e.g., Internet traffic). For these reasons, the European
Telecommunications Standards Institute (ETSI) has standardized the
General Packet Radio Service, which is based on packet switching
By adding GPRS to the GSM network, operators can offer efficient wireless
access to external IP-based networks, such as the Internet and corporate
intranets.
5
GPRS
General
Necesidad: EVOLUCIÓN DE LOS SERVICIOS DE DATOS
Propuesta:
telefonía móvil celular + tx radio basada en la
conmutación de paquetes
Acción: El ETSI crea el estándar GPRS
Resultados: ACCESO MÓVIL A REDES IP DE DATOS MÁS
EFICIENTE
6
6
GPRS
Introduction:
: Data
GPRS -- Introduction
Introduction:
Data market
market
160
60
Internet access (millions)
140
Laptops sales(millions)
50
120
40
100
Data Market
Growth
80
30
60
20
40
10
20
0
0
1996
1997
1998
1999
2000
USA
Europe
1996
1997
1998
1999
2000
World
7
This slide shows the growing sales of laptops and Internet users in the last
five years. We can see that both markets have experienced a very rapid
growth, so these statistics and the fact that actually the number of cellular
telephones is superior to fixed ones, points to a successful new market of
wireless data services.
7
GPRS
Introduction:
: Data
Introduction:
Data in
in GSM
GSM
? STARTING
POINT:
Short
Services.
Message
- Mobile access data
transmission.
? TECHNICAL
PROBLEMS:
- Excessive latency.
- Limited bandwidth
(GSM data transmission
rate: 9600bps and SMS
data transmission rate :
160bps).
? LACKS:
- Faster, more secure
and more reliable
transmission
mechanisms over GSM.
?New data technologies development over 2G+ GSM networks:
- Circuit switched - based systems (HSCSD).
- Packet switched - based systems (GPRS).
8
Not many months ago, data services over GSM were limited to short
messages and mobile access data transmissions. The main problems were
the excessive latency that is, the time that the connection set- up takes, and
the slow data rates. These limitations and the lack of faster, more secure and
more reliable devices were the motives that stimulate the development of
new data technologies such as High Speed Circuit Switched Data, based on
circuit switching and the General Packet Radio Service, based on packet
switching.
8
GPRS
Introduction:
: Circuit
Circuit-switching
Introduction:
Circuit-switching
vs.
Packet-switching
vs. Packet
Packet-switching
Circuit-switching
Packet-switching
9
Up to now, I have been talking about circuit-switched communication and
packet-switched communication. Now I am going to explain the differences
between these two technologies.
For circuit-switched communication, one radio channel is allocated to a
mobile station when the user wants to transmit data through a network. This
channel is permanently allocated for a particular user during the entire call
period, whether data is transmitted or not, and the user has to pay for the
total connection time. Circuit-switched communication is suitable for data
traffic where a constant bandwidth data flow is needed or when transmitted
data are sensitive to even small connection delays, like for example, video
transmissions.
For packet-switched communication, the channels are only allocated to a
MS when data packets are sent or received, and they are released after the
transmission. When a Mobile Station (MS) generates a data packet, the
network forwards the packet to its addressee on the first available radio
channel. Several mobile stations can share one radio channel and when a
message consists of large data quantities, it is divided into several packets
that can use different radio channels during transmission. When these
packets reach their destiny, they are reassembled to form the original
message.
It is obvious that for bursty traffic, packet-switched bearer services result in
a much better utilization of the traffic channels.
9
GPRS – Introduction
Introduction:: HSCSD
HSCSD (High Speed Circuit Switched Data) characteristics:
?
?
?
?
?
Higher data transmission rates: 14.4 kbps/channel.
Theoretical maximun speed of 57.6kbps: a single user
simultaneous access to multiple channels (up to 4) .
Easier to implement than GPRS: only software upgrades.
Circuit switched-based
Unsuitable to bursty data traffic ? considered as a previous
step to GPRS.
10
Now we are going to see one of the new tecnologies which where developed
in order to solve the limitations of GSM. HSCSD is based on circuit
switching and from the user’s point of view, is not more than an
improvement of the actual GSM data services, with the difference of higher
transfer rates of up to 14.4 kbps and channel (14.4 kbps/channel).
But besides this, HSCSD gives a single user simultaneous access to up to
four multiple channels at the same time, while traditional GSM only
supports one user per channel. Remember that a physical channel is defined
by the recurrence of one particular time slot. So, assuming a standard
transmission rate of 14.4 kbps and using four timeslots, this system provides
a theoretical data radio transmission of up to 57.6kbps. (This transmission
rate is broadly equivalent to one ISDN B-Channel).
HSCSD is generally easier to implement in mobile networks than GPRS
because HSCSD only requires a software upgrade of base stations and no
new hardware is needed.
The drawback of HSCSD results from the fact that it is based on circuit
switching and that is the reason why this bearer system is more adequate for
data traffic that requires a constant bandwidth data flow or that is sensitive
to small connection delays. HSCSD should, for example, be chosen fo r
videoconferences. But in case of bursty traffic, this way of transmitting data
is unsuitable and results in highly inefficient resource utilization. For all of
this items, HSCSD is not very efficient and it has been considered as a
previous step to GPRS.
10
GPRS – Introducción: GPRS
The GPRS (General Packet Radio Service) service provides:
?
?
?
?
packet switched-based.
?
efficient use of scarce radio resources.
?
efficient wireless access to external IP-based networks
(Internet, intranets).
shortest access times (below one second).
Faster data rates (theoretical maximun speed of 171,2
kbps = 21,4kbps/ timeslot x 8 timeslots).
a flexible service, with volume-based (or session durationbased) charging ? user-friendlier billing.
11
GPRS is a new bearer service for GSM that provides a packet-based access
in which the scarce radio resources are reserved only when necessary and
each channel can be shared by many users. Besides, up and downlink
channels are allocated independently of each other. GPRS also improves
and simplifies wireless access to packet data networks based either on X.25
or on the Internet Protocol. Although I must point that this presentation is
focused on IP packet data networks, such as the Internet and corporate
intranets.
GPRS applies a packet radio principle to transfer user data packets in an
efficient way between GSM mobile stations and external packet data
networks. Users of GPRS benefit from shorter access times and higher data
rates in contrast with conventional GSM, where the connection set- up takes
several seconds and rates for data transmission are restricted to 9.6 kbit/s.
GPRS in practice, offers session establishment times below one second and
data rates up to several ten kbit/s.
In addition, GPRS packet transmission offers a user- friendlier billing
system, based on the amount of transferred data, instead of on the duration
of the connection. The time-based charging is unsuitable for applications
with bursty traffic because the user must pay for the entire airtime, even for
idle periods when no packets are sent (for example, when the user reads a
Web page). The advantage of this new billing system for the user is that he
or she can be “online” over a long period of time but will be billed based on
the transmitted data volume.
11
GPRS
Introducción:
: The
GPRS -- Introducción
Introducción:
The GSM
GSM radio
radio
steps
steps to
to 3rd
3rd generation
generation
Introduction of 3rd generation radio (UMTS)
2001-2002
gy
o
New multimedia services (WCDMA)
l
o
hn
c
2000-2001
Te
o
i
d
EDGE (up to 384 kbps)
a
f R 1999-2000
o
t
en
GPRS (up to 171 kbps)
m
p
o
Bluetooth (short-range wireless communications)
l
ve 1998-1999
De
HSCSD (up to 57.6 kbps)
1994-1997
SMS over GSM radio channels (9.6 kbps)
Evolution of GSM Platform
12
Bluetooth is a global de facto standard for wireless connectivity based on a
short-range radio link (up to 10 meters). That means that two Bluetooth
equipped devices within 10 meters range of each other can establish a
connection together and they don’t require a line-of-sight connection
because Bluetooth utilized a radio-based link. Opera en la fcia. de 2.4Ghz y
a velocidades de hasta 721Kbps (real/ a 200 y 400Kbps q es poco).
EDGE (Enhanced Data rates for GSM Evolution) is another high-speed
mobile data standard. It allows data transmission speeds up to 384 kbps
(when all eight time-slots are used).
As you know, a mix of FDMA and TDMA, combined with frequency
hopping, has been adopted as the multiple access scheme for GSM. The
multiple access scheme defines how different simultaneous communications
between several mobile stations in different cells, are sharing the GSM radio
spectrum. Using FDMA, the available frequency band is divided into
individual frequencies, also call channels and each frequency is assigned to
a user. So the larger the number of users in a FDMA system, the larger the
number of available frequencies must be. The limited available radio
spectrum and the fact that a user will not free its assigned frequency until he
does not need it anymore, explain why the number of users in a FDMA
system can be rapidly limited.
On the other hand, TDMA allows several users to share the same channel,
and in order to increase the efficiency of the communication each frequency
or channel is divided into so-called time slot. The recurrence of one
particular time slot in every frame defines a physical channel.
12
GPRS
Introducción: Ratio
Ratio
Availability/
Availability
/Capacity
Availability/Capacity
WCDMA
(UMTS)
<470 kbps
Evolution
384 - 2048 kbps
EDGE
EGPRS
GPRS
HSCSD
GSM
Data
WCDMA
Phase I
9 - 53.6 kbps
144 - 384 kbps
9.6 - 28.8 kbps
9.6 kbps
1998
1999
2000
2001
13
In the initial release, GPRS uses the same modulation as GSM (GSMK), but
the subsequent evolution of packet-based services in GSM introduces
EDGE technology.
In the evolution to UMTS, Wideband Code Division Multiple Access
(WCDMA) has been implemented.
As an access method, Code Division Multiple Access (CDMA) is an
alternative to TDMA. However, there are several key differences in
implementation between TDMA and CDMA. The basic concept of CDMA
is to simultaneously handle several users without dividing the radio carrier
by timeslots. Instead, each MS is given a decoding key. Then the
information for several MSs is transmitted downlink at the same time and
each MS must analyse the information and decode only that one which is
relevant to it. Security is ensured as each MS does not have the decoding
key for other MSs and will be only able to decode its own information.
The problem of interference is solved using such intelligent functions, but
as the number of users of the same carrier increases, the more difficult it
becomes for a MS to decode its own information. For this reason, it is
desirable to have a wide bandwidth when using CDMA solutions. This leads
to the term WCDMA. Given the large bandwidth, each WCDMA terminal
connection may access several devices simultaneously.
13
GPRS
Introducción: Comparativa
Comparativa
Standards
Implementation
GSM Data
9.6 kbps
9.6 kbps
HSCSD
57.6 kbps
28.8 kbps
GPRS
171 kbps
57.6 kbps
EDGE
470 kbps
< 470 kbps
WCDMA
2048 kbps
384 kbps
14
This slide shows the theoretical transfer rates given by the standards and the
real expected bit rates.
14
GPRS
Introducción: Simultaneos
Simultaneos
usage
usage of
of PS
PS and
and CS
CS services
services
In a GSM/GPRS network, three classes of mobile stations have
been defined:
A Class A mobile station supports simultaneous operation of
GPRS and conventional GSM services.
?
A Class B mobile station is able to register for GPRS or
conventional GSM services simultaneously, but it can only use
one of the two services at a given time.
?
A Class C mobile station can attach for either GPRS or
conventional GSM services. Simultaneous registration (and
usage) is not possible.
?
15
The interaction of GPRS services with CS connections have three possible
modes of operation:
Class A mode of operation allows a MS to have a circuit switched
connection at the same time as it is involved in a package trans fer.
Class B mode of operation allows a MS to be attached to both CS and PS
but it can not use both services at the same time. However, MS that is
involved in a package transfer can receive a page for circuit switched traffic.
The MS can then suspend the packet transfer for the duration of the circuit
switched connection and afterwards resume the package transfer.
Class C mode of operation allows a MS only to be attached to one service at
the time. A MS that only supports GPRS and not circuit switched traffic will
always work in class C mode of operation.
15
GPRS - Introducción : Área de cobertura
Base Station
Coding
scheme
Data rate
(kbits/s)
CS-1
9.05
CS-2
13.4
CS-3
15.6
CS-4
21.4
Cell Radius
CS1 (1.06)
GSM Voice (1)
CS2 (0.82)
CS3 (0.72)
CS4 (0.42)
There
Thereisisno
noimportant
importantcoverage
coveragechanges
changesbetween
betweenGSM
GSMand
andGPRS
GPRSusing
usingCS1
CS1and
andCS2
CS2
16
Channel coding is used to protect the transmitted data packets against errors.
The channel coding technique in GPRS is quite similar to the one employed
in conventional GSM.
Four different channel-coding schemes have been defined for GPRS to
make optimum use of varying radio conditions. For the coding of the traffic
channel (PDTCH), one of the four coding schemes is chosen, depending on
the quality of the channel. Under very bad channel conditions, we may use
CS-1 and obtain a data rate of 9.05 kbit/s per GSM timeslot (per channel),
but a very reliable coding. CS-1 is also used for the coding of the signa lling
channels. Under good channel conditions, CS-4 should be used and with
eight timeslots per user, we obtain a maximum data rate of 171.2 kbit/s. In
practice, multiple users share the time slots, and thus, a much lower bit rate
is available to the individual user.
For example, approximately 40 kbit/s per user will be achieved, if three
users share the time-slots and CS-3 is employed.
16
GPRS - Introducción : Diferentes Áreas
Location Area (LA) & Routing Area (RA)
LA
RA1
RA2
A Location Area (LA) is a group
of Routing Areas (RA)
RA3
17
In a cellular system, such as GSM and GPRS, the covering area of an
operator is divided into cells. A cell corresponds to the radio coverage of a
BTS. A group of cells served by a single MSC/VLR, defines a Location
Area (LA).
A LA in a GPRS system is divided into several Routing Areas, controlled by
different SGSNs.
17
Why
Why GPRS
GPRS ??
GPRS
GPRS philosophy
philosophy
18
In this section we are going to see the reasons why GPRS has been chosen
as the optimal solution to the new wireless data services.
18
GPRS
GPRS -- Why
Why ?:
?: Questions
Questions
?
Other technologies
(EHSCSD).
have
been
skipped:
HSCSD
?
New equipment is required.
?
It implicates a phylosophy change: Circuit Switched Data –
Packet Switched Data.
?
UMTS - WCDMA seems to be very close.
19
19
GPRS
GPRS -- Why
Why ?:
?: Answers
Answers
?
Represents the first true convergence of the mobile and
data worlds.
?
Covers the growing demand of data services in the most
efficient way.
?
Greatly improves and simplifies wireless access to packet
data networks.
?
Requires the minimum capacity/equipment relationship.
?
Is the first step towards the Universal Mobile
Telecommunication System (UMTS) with the minimum
cost.
20
20
GPRS
Why?:
?: Data
GPRS -- Why
Why?:
Data Traffic
Traffic
Bursty traffic
Data Circuit Utilization
bit/s
Capacity (Mbytes)
Web Traffic
Circuit
Capacity
33.6k
t
Mean
Web Navigation example
Used
Available*
% Usage
Email
(Discharge)
0.99
9.7
10.2
Email
0.06
3.0
2.0
0.23
4.2
5.5
(On-line
Reading)
• The user transmits/receives
bursty traffic
e.g. Web navigation
• Internet has variable delay
Web
(Navigation)
* 56.6 Kbits/s
• PSTN (CSD) channel is underused
21
GPRS is designed to support transmission of intermittent and bursty traffic
transfers as well as occasional transmission of large volumes of data. The
most common application of GPRS is expected to be Internet/intranet
access.
The graph shows an example of Web navigation over GSM. We can
appreciate the bursty traffic transfer and the main utilization of the circuit
that clearly indicates that the channel is underused. It is easy to come to the
same conclusion analysing the information of the diagram on the right. The
last column shows the data circuit utilization percentage and it also points to
an inefficient use of the resources.
21
GPRS
Why?:
?: Permanent
GPRS -- Why
Why?:
Permanent Data
Data Circuits
Circuits
Authentication
Server
E-mail
Server
Email via GSM
Cellphone
Modem
GSM
Authentication
Server
Internet
GPRS
Virtual GPRS data tunnel
INITIAL CALL PROCESS
•
•
•
•
GSM call
Modem Negotiation
Login to the server
E-mail discharge
Total
E-mail
Server
Móvil
Modem
PSTN
Email via GPRS
Time (s)
4
30
11
180
3 min 45s
FOLLOWING CALLS
• Repeat the above mentioned steps: 3 min 45s
INITIAL CALL PROCESS
• GPRS call
• Login to the server
• E-mail discharge
Total
Internet
Always on connection
(permament authentication)
Time (s)
4
11
180
3 min 15s
FOLLOWING CALLS
• Always on-line – Virtual circuit: Undeterminated
22
This slide compares the e- mail service via GSM and via GPRS. We can
appreciate that the initial call process lasts more or less the same in both
cases, but the advantage of GPRS is the characteristic “always on”, that
allows the user to be connected indefinitely to the e- mail server. This
characteristic also avoids the authentication process and the connection time
in following calls. So, end-users of GPRS will improve their perception of
the service, and will be charged in base on the amount of transmitted data,
instead of on the duration of the connection, which would not be economical
(cost-effective).
22
GPRS
Why?:
?: Equipment
GPRS -- Why
Why?:
Equipment -- Coverage
Coverage
area
area -- B/W
B/W Relationship
Relationship
Technology Standar
ndard
d
GSM
Delay
Equipment
Equip
ment
Spectr
pectrum
um
B/W
Coverage
Co
verage
Now
HSCSD
Now
GPRS
Now
EDGE
Very soon
UMTS
In evolution
x4
x4
x20
x40
23
This slide shows a comparative of the technologies that have been
previously mentioned.
GPRS requires the minimum capacity/equipment relationship. The black
antenna symbolizes the new hardware device that is required to support
GPRS. The green antenna indicates the new EDGE modulation, and the
yellow one represents the new modulation of UMTS.
23
GPRS
GPRS Logical
Logical Architecture
Architecture
24
In the following slides, we are going to see the GPRS logical architecture,
explaining the role of each component in the GPRS system and the way that
they interchange with.
--------------------------------------------------------------------GSM distinguishes explicitly between user and equipment and deals with
them separately. The international mobile station equipment identity (IMEI)
uniquely identifies a mobile station internationally. It is a kind of serial
number. The IMEI is allocated by the equipment manufacturer and
registered by the network operator who stores it in the EIR. Each registered
user is uniquely identified by its international mobile subscriber identity
(IMSI). It is stored in the subscriber identity module (SIM). A mobile
station can only be operated if a SIM with a valid IMSI is inserted into
equipment with a valid IMEI. The “real telephone number” of a mobile
station is the mobile subscriber ISDN number (MSISDN). It is assigned to
the subscriber (his or her SIM, respectively), such that a mobile station set
can have several MSISDNs depending on the SIM.
24
GPRS
Architecture
: Basic
GPRS Logical
Logical Architecture:
Architecture:
Basic GSM
GSM
GSM basic network architecture
MSC
GMSC
PSTN
MS
BTS
BSC
EIR
AUC
HLR
VLR
25
This figure shows the system architecture of a GSM public land mobile
network (PLMN) with essential components. A GSM mobile station is
denoted as MS. A cell is formed by the radio area coverage of a base
transceiver station (BTS). Several BTSs together are controlled by one base
station controller (BSC). The BTS and BSC together form the base station
subsystem (BSS). GSM networks are structured hierarchically. They consist
of at least one administrative region, which is assigned to a MSC. Each
administrative region is made up of at least one location area (LA). A
location area consists of several cell groups. Each cell group is assigned to a
BSC. Several data bases are available for call control and network
management: the home location register (HLR), the visited location register
(VLR), the authentication center (AUC), and the equipment identity register
(EIR). For all users registered with a network operator, permanent data
(such as the user’s profile) as well as temporary data (such as the user’s
current location) are stored in the HLR. In case of a call to a user, the HLR
is always first queried, to determine the user’s current location. A VLR is
responsible for a group of location areas and stores the data of those users
who are currently in its area of responsibility. The AUC generates and stores
security-related data such as keys used for authentication and encryption,
whereas the EIR registers equipment data rather than subscriber data.
Ver nota de transparencia anterior (sigue).
25
GPRS
Architecture
: GPRS
GPRS Logical
Architecture:
GPRS
GPRS basic network architecture
MSC
BTS
BSC
HLR
PSTN
VLR
Intranet
PCU
GPRS Core
SGSN
GPRS
Backbone
IP Network
GGSN
Internet
26
A GPRS network can be seen as an extension of a GSM system but it
requires some additions specific to the GPRS network.
In order to integrate GPRS into the existing GSM architecture, a new class
of network nodes, called GPRS support nodes (GSNs), and a new device
call Packet Control Unit (PCU), have been introduced.
GPRS Support Nodes (GSNs) are responsible for the delivery and routing of
data packets between the mobile stations and the external packet data
networks (PDN). These nodes are the Serving GPRS Support Node (SGSN)
and the Gateway GPRS Support Node (GGSN). They work with the Home
Location Register (HLR), the Mobile Switching Center (MSC) and Base
Station Subsystems (BSSs).The GGSN, which is the interconnection point
for packet data networks, is connected to the SGSN via an IP backbone.
User data – for example, from a GPRS terminal to the Internet – is sent
encapsulated over the IP backbone.
The BSC requires a Packet Control Unit to handle GPRS packets. Apart
from the BSC, which requieres a hardware update, the existing GSM
network solely requieres software upgrades to support GPRS.
26
GPRS
Architecture
:
GPRS Logical
Architecture:
Adaptation
Adaptation to
to GPRS
GPRS
?
New nodes:
- SGSN (Serving GPRS Support Node)
- GGSN (Gateway GPRS Support Node).
?
New hardware:
- The BSC requires a PCU (Packet Control Unit).
?
Software upgrade:
- BSC/BTS (Base Station Controller/Base Transceiver Station).
- HLR (Home Location Register).
- MSC (Mobile Switching Center).
27
For the introduction of GPRS in GSM networks, it is necessary to modify
the GSM system in various ways: two new nodes should be introduced for
handling packet switching and apart from the BSC, which requires a
hardware upgrade, the existing GSM network only requires software
upgrades to support GPRS.
27
GPRS
Architecture
:
GPRS Logical
Architecture:
New
New nodes
nodes -- SGSN
SGSN
The Serving GPRS Support Node (SGSN) is a primary
component in the GSM network using GPRS and is a new
component in GSM. It provides:
?
packet routing and transfer between each MS within its
service area and the GGSN.
?
mobility management (attach/detach, user authentication,
ciphering, location management, etc.)
?
session and GPRS radio resource management.
?
logical link towards the MS.
?
output of charging data.
28
A serving GPRS support node (SGSN) is responsible for the delivery of data
packets from and to the mobile stations within its service area. Its tasks
include to route and transfer packets between mobile terminals and the
GGSN, to perform mobility management for GPRS terminals, including
processes of attach/detach, user authentication, ciphering, location
management (cell updating and routing area updating) and so on.
The location register of the SGSN stores location information (e.g., current
cell, current VLR) and user profiles (e.g., IMSI, address(es) used in the
packet data network) of all GPRS users registered with this SGSN.
The SGSN is also responsible for the session management that enables a
end-to-end data packet exchange between a MS and a PDN, so user data are
transferred transparently between the MS and the packet data network.
Opening a session is known as PDP context activation.
This node also provides logical link management towards each MS. The
logical link carries user packet traffic, SMS traffic and layer 3 signalling
between the network and the GPRS terminal.
SGSN also collects charging information (volume and duration) for each
MS in a Charging Data Record (CDR).
28
GPRS
Architecture
:
GPRS Logical
Architecture:
New
New nodes
nodes -- GGSN
GGSN
The GGSN provides:
?
?
the interface towards the external IP packet networks.
GPRS session management; communication set-up towards
external networks.
functionality for associating the subscribers to the right
SGSN.
?
?
output of charging data.
29
A Gateway GPRS Support Node (GGSN) acts as an interface between the
GPRS backbone network and the external packet data networks. The main
functions of the GGSN are to set up communication with external packet
data networks, to authenticate users to them, to route and tunnel packets to
and from the SGSN and to generate charging data.
It converts the GPRS packets coming from the SGSN into the appropriate
packet data protocol (PDP) format (e.g., IP or X.25) and sends them out on
the corresponding packet data network. In the other direction, PDP
addresses of incoming data packets are converted to the GSM address of the
destination user. The readdressed packets are sent to the responsible SGSN.
For this purpose, the GGSN stores the current SGSN address of the user and
his or her profile in its location register.
29
GPRS
Architecture
:
GPRS Logical
Architecture:
New
New hw
hw -- PCU
PCU
The PCU (Packet Control Unit) is responsible for the Radio
Link Control (RLC) and Medium Access Control (MAC) layers
over the air interface. It manages:
?
packet data channel allocation to MSs.
?
transfer of user data packets between MSs and the SGSN.
?
packet segmentation/re-assembly and scheduling.
?
radio channel access control and management.
?
transmission error detection and retransmission (ARQ).
30
The PCU is responsible for the GPRS packet data radio resource
management in the BSS. In particular the PCU is responsible for handling
the Medium Access Control (MAC) and Radio Link Control (RLC) layers
of the radio interface.
The data link layer between the MS and the network is divided into two
sublayers: the Logical Link Control (LLC) layer, between a MS and a
SGSN, and the RLC/MAC layer, between the MS and the BSS.
The logical link control (LLC) layer provides a highly reliable logical link
between a MS and its assigned SGSN. Its functionality includes sequence
control, in-order delivery, flow control, detection and transmission error and
retransmission of data packets if necessary.
The RLC/MAC layer at the air interface includes two functions. The main
purpose of the radio link control (RLC) layer is to establish a reliable link
between the MS and the BSS. This includes the segmentation and
reassembly of LLC frames into RLC data blocks and ARQ (Automatic
Repeat Request) of incorrect code words. The medium access control
(MAC) layer controls the access attempts of a MS on the radio channel
shared by several MSs.
To sum up, the PCU is responsible for assigning channels to GPRS MSs, for
transmitting data packets between the MS and the SGSN including
processes of segmentation, re-assembling and retransmission of erroneous
packets and for controlling and managing the radio channel.
30
GPRS
Architecture
:
GPRS Logical
Architecture:
New
New software
software
?
BSS (Base Station Subsystem) = BSC and a BTS:
?
The BTS is the radio equipment which transmits and
receives information to and from the MSs.
?
The BSS controls a group of BTSs and provides all the
radio-related functions.
HLR (Home Location Register) is a permanent data base
which contains GPRS subscription data and routing
information.
?
MSC (Mobile Switching Center) performs the switching
functions of the GSM network. It also provides connection to
other networks.
?
31
The GSM elements that require a software upgrade to support GPRS are the
BSS, the HLR and the MSC. The Base Station Sub-system (BSS) consists of
a Base Station Controller (BSC) and a Base Transceiver Station (BTS). The
BTS is the radio equipment that transmits and receives information. This
element is represented like an antenna. The BTS must contain GPRSspecific software. It separates the MS-originated circuit-switched calls from
packet data communication before the BSC forwards CS calls to the MSC,
and PS data to the SGSN. A group of BTSs is controlled by a BSC. The
BSC provides all the radio-related functions. It has the functionality to set
up, supervise and disconnect circuit-switched and packet-switched calls. It
is a high capacity switch that provides functions including handover, cell
configuration data, and channel assignment. As with the BSS, the software
in the HLR must be upgraded to support GPRS. The Home Location
Register (HLR) is the database that holds subscription information for every
person who has bought a subscription from the GSM/GPRS operator. It
stores information for CS and for PS communication and contains
information about, for example, authentication parameters, and whether or
not packet communication is allowed. In addition, the HLR includes
information about the location of the MS. The Mobile services Switching
Centre (MSC) performs the telephony switching functions of the GSM
circuit-switched system, like the SGSN switches the GSM packet-switched
traffic. It controls calls to and from other telephony and data systems, such
as the Public Switched Telephone Network (PSTN), ISDN, PLMN, PDN
and possibly some private networks.
31
GPRS
Architecture
:
GPRS Logical
Architecture:
GPRS
GPRS Network
Network
SMS - SC
GPRS basic network architecture
MSC/VLR
HLR
MS
BTS
BSC
Internet
SGSN
GGSN
Signalling and data
Signalling
CDR Collection
New nodes
New hardware (PCU)
New software
Billing
Gateway
GPRS Backbone
IP Network
Corporate
Network
32
This slide shows the interconnections of the previous mentioned GPRS
elements and two more ones: the Short Message–Service Centre (SMS-SC),
which forwards SMS messages to a MS via the GPRS radio channels and
the Billing Gateway (BG), which is in charge of charging and stores the
Charging Data Records (CDR) generated by the GSNs.
The IP-based GPRS Backbone provides the indirect data paths between all
GSNs (GPRS Support Nodes). This reduces the number of direct physical
channels needed by a GSN to communicate with its peers.
Within this backbone, the GSNs encapsulate the PDN packets and transmit
(tunnel) them using the GPRS Tunneling Protocol (GTP). This protocol
provides a transparent transmission of user and signalling data betweeen
GSNs.
32
GPRS
GPRS -- Logical
Logical Architecture
Architecture ::
GPRS
GPRS Backbone
Backbone
BSC
MS
BSC
BTS
BTS
Inter-PLMN
GPRS backbone
SGSN
SGSN
PLMN 1
Intra-PLMN
GPRS backbone
Border
Gateway
(BG)
GGSN
Border
Gateway
(BG)
Packet Data Network (PDN)
(e.g. Internet, intranet)
PLMN 2
Intra-PLMN
GPRS backbone
GGSN
Host
SGSN
Router
Lan
33
There are two kinds of GPRS backbones:
• Intra-PLMN backbone networks connect GSNs of the same PLMN and are
therefore private IP-based networks of the GPRS network provider.
• Inter-PLMN backbone networks connect GSNs of different PLMNs. A
roaming agreement between two GPRS network providers is necessary to
install such a backbone. This slide shows two intra-PLMN backbone
networks of different PLMNs connected with an inter-PLMN backbone. The
gateways between the PLMNs and the external inter-PLMN backbone are
called border gateways. Among other things, they perform security
functions to protect the private intra-PLMN backbones against unauthorized
users and attacks.
We can see two possible ways to access the host: one that uses the IntraPLMN backbone and another that goes through the Inter-PLMN backbone.
We analyse this situations in the roaming section.
33
GPRS - Logical Architecture:
Architecture: BG nodes
The Border Gateway provides the following set of functions:
?
Inter-PLMN routing and packet forwarding functions.
?
Charging data collection functions.
?
Security functions to protect the private intra-PLMN
backbones against unauthorized users and attacks.
34
- This set of functions allows IP packets to be routed and forwarded between
GSNs belonging to different PLMN.
- This functions allows inter-PLMN charging.
34
GPRS
Architecture
: Backbone
GPRS -- Logical
Architecture:
Backbone cloud
cloud
SGSN1
GGSN1
SGSN3
Intra-PLMN
GPRS backbone
SGSN1
Inter-PLMN
GPRS backbone
Inter-PLMN
GPRS backbone
GGSN1
Single GPRS
backbone cloud
SGSN2
GGSN2
SGSN3
GGSN3
Intra-PLMN
GPRS backbone
SGSN2
GGSN2
GGSN3
35
All the GPRS backbone structure, with intra and inter-PLMN GPRS
backbones, could be seen as a single GPRS backbone cloud, so there is a
one-to-all relationship between each SGSN and all the GGSNs.
35
GPRS
Architecture
: Possibilities
GPRS Logical
Architecture:
Possibilities
Proprietary Gb interface
A
BTS
MSC/
VLR
BSC
GMSC
SGSN
PCU
Gb
GGSN
Gn
Gi
Integrated MSC - SGSN
Integrated GSNs
A
BTS
A
BSC
MSC/
VLR
GMSC
PCU
SGSN
GGSN
Gb
Gn
BTS
Gi
BSC
MSC/
VLR
GMSC
PCU
SGSN
GGSN
Gb
Gn
Gi
36
There are different possibilities to implement the nodes. In the square on
top, we can see that the PCU and the SGSN are integrated into the same
structure. Another possibility is to integrate the MSC and the SGSN, as we
can see in the square below on the left hand side. This is the most normal
situation. And finally, other possibility is to combine in the same structure
the SGSN and the GGSN. This situation is showed in the square below in
the right hand side.
36
Protocols and Interfaces
37
In this section we are going to see the GPRS interfaces between the new
network nodes and the GSM network.
37
GPRS
GPRS -- Interfaces
Interfaces
GPRS reference model
SMS - GMSC
SMS - IWMSC
SM - SC
E
C
Gd
D
MSC/VLR
MS
TE
Gs
A
MT
R
HLR
Gr
Gc
BSS
Um
SGSN
Gb
TE
PDN
GGSN
Gn
Gi
Gn
Gp
Signalling and data
Signalling
Gf
EIR
SGSN
GGSN
Other PLMN
38
The European Telecommunications Standards Institute (ETSI) has defined the
GPRS interfaces. The Gb interface connects the BSC with the SGSN. Via the Gn
and the Gp interfaces, user data and signalling data are transmitted between the
GSNs. The Gn interface will be used if SGSN and GGSN are located in the same
PLMN, whereas the Gp interface will be used if they are in different PLMNs. These
two interfaces are also defined between two SGSNs. This allows the SGSNs to
exchange user profiles when a mobile station moves from one SGSN area to
another. Across the Gf interface, the SGSN may query the IMEI of a mobile station
trying to register with the network. The Gi interface connects the PLMN with
external public or private PDNs, such as the Internet or corporate intranets.
Interfaces to IP (IPv4 and IPv6) and X.25 networks are supported. The HLR stores
the user profile, the current SGSN address, and the PDP address(es) for each GPRS
user in the PLMN. The Gr interface is used to exchange this information between
HLR and SGSN. For example, the SGSN informs the HLR about the current
location of the MS. When the MS registers with a new SGSN, the HLR will send
the user profile to the new SGSN. The signaling path between GGSN and HLR is
the Gc interface. It may be used by the GGSN to query a user’s location and profile
in order to update its location register. In addition, the MSC/VLR allow efficient
coordination between PS (GPRS) and CS (conventional GSM) services. Examples
of this are combined GPRS and non-GPRS location updates and combined
attachment procedures. Moreover, paging requests of circuit switched GSM calls
can be performed via the SGSN. For this purpose, the Gs interface connects the
databases of SGSN and MSC/VLR. To exchange messages of the short message
service (SMS) via GPRS, the Gd interface is defined. It interconnects the SMS
gateway MSC (SMS-GMSC) with the SGSN.
38
GPRS transmission plane protocol stack
MS
BSS
SGSN
GGSN
Application
Network layer
IP / X.25
Network layer
IP / X.25
SNDCP
DATA
LINK
LAYER
LLC
RLC
MAC
PHYSICAL
LAYER
Um
GTP
GTP
LLC
UDP/
TCP
UDP/
TCP
RLC
BSSGP
BSSGP
IP
IP
MAC
Frame
Relay
Frame
Relay
L2
L2
L1 bis
L1 bis
L1
L1
GSM RF
GSM RF
SNDCP
Gb
SNDCP Subnetwork Dependent Convergence Protocol
LLC
Logical link control
RLC
Radio Link Control
MAC
Medium Access Control
BSSGP BSS GPRS aplication Protocol
Gn
GTP
TCP
UDP
IP
Gi
GPRS Tunneling Protocol
Transmision Control Protocol
User Datagram Protocol
Internet Protocol
39
In order to reach their final destination, data coming from external network
are tunnelled twice: into GTP packets in the Core Network and into LLC
frames (SNDCP allows multi-protocol) in the Access Network.
39
Protocols used in the transmission plane I
?
BSS GPRS Protocol (BSSGP)
? transmission of routing and QoS information between BSS and
SGSN.
?
Radio Link Control (RLC)
? error correction (retransmission).
?
Medium Access Control (MAC)
? scheduling of access attemps and queuing of accesses.
? mapping of RLC/MAC blocks onto logical channels.
40
40
Protocols used in the transmission plane II
?
GPRS Tunneling Protocol (GTP)
? transparent transmission of user and signalling data between GSNs.
?
Transmission Control Protocol (TCP) / User Datagram
Protocol (UDP)
?
Internet Protocol (IP)
?
Subnetwork Dependence Convergence Protocol (SNDCP)
? data compression and fragmentation.
?
Logical Link Control (LLC)
? ciphering.
41
41
GPRS - Protocols and Interfaces:
Transmission Plane
X25 end to end
IP end to end
LLC tunnel layer
GTP tunnel layer
RADIO specific
GPRS IP backbone
L2
3 layer stack
SGSN
GGSN
One of the initial requirements of GPRS was to support as well IP as X.25. That is the
reason why the GPRS backbone design was not optimized for the Internet Protocol and a
tunneling protocol was created. As a result, the GPRS transmission plane is
characterized to have a three-layer stack (for example, TCP -> IP -> GTP -> TCP -> IP is
a case supported by the GPRS backbone).
42
42
GPRS - Protocols and Interfaces:
Tunneling and Mobility
HLR
BTS
External
data
network
VLR
BSC
Gr
Gs
LLC 1
Gi
BTS
Abis
Gb
BSC
LLC 2
Gn
SGSN
GGSN
GTP 1
GTP 2
BTS
BSC
SGSN
LLC 3
The double level of tunneling corresponds to a double level of mobility management:
LLC manages the micromoblity and GTP manages the macromobility.
43
Cambio de BSC = micromovilidad.
Cambio de SGSN = macromovilidad.
43
GPRS Attach and
PDP Context Activation
44
In this section, it is described how a MS registers with the GPRS network
and becomes known to an external data packet network (PDN).
To exchange data packets with external PDNs after a successfull GPRS
attach, a MS must obtain an address used in the packet data network (a PDP
address) and create a PDP context. The PDP context describes the
characteristics of the connection to the packet data network. It contains the
PDP type (e.g., IPv4), PDP address asigned to the MS, the requested QoS,
and the address of a GGSN that acts as the access point to the PDN.
With an active PDP context, the MS is “visible” for the external PDN and is
able to send and receive data packets.
Packets from the external packet data network will be routed to the GGSN,
which then tunnels them to the current SGSN of the mobile user.
44
GPRS
GPRS Attach
Attach
3
2
3
MS
1
1
2
2
4
BTS
HLR
3
MSC/VLR
4
SGSN
GGSN
Packet Data
Network
BSC
GPRS
Backbone
1.- La estación móvil solicita la conexión a la red GPRS. La petición, que se envía al SGSN,
contiene datos como tipo de terminal GPRS, cifrado que soporta , si la conexión es GPRS, GSM
o combinada, etc).
2.- La red comprueba si el usuario esta autorizado y el HLR envía su perfil al SGSN.
3.- Los datos del terminal móvil como usuario de la red GPRS son intercambiados entre el HLR,
el MSC/VLR y el SGSN.
45
4.- El SGSN informa a la MS de que su petición de acceso a la red se ha realizado.
GPRS attach and PDP context activation must be executed in order for
GPRS users to connect to external packet data networks. Before a GPRS
mobile station can use GPRS services, it must register with a SGSN of the
GPRS network. The network checks if the user is authorized and copies the
user profile from the HLR to the SGSN. This procedure is call GPRS attach
and it consist basically in setting up a link between a MS and a SGSN.
Once the terminal is attached to the network, the network knows its location
and capabilities. If the unit is a class A or class B terminal, then circuitswitched IMSI and GPRS attach procedures can be performed at the same
time. The mapping between the two addresses (PDP and IMSI) enables the
GGSN to transfer data packets between PDNs and MSs.
The GPRS attach procedure follows the following steps:
1. The MS requests that it wants to be attached to the network. The
terminal´s request, which is sent to the SGSN, indicates whether it wants to
attach to a packet-switched service, a circuit-switched service, or to both.
2. Authentication is made between the terminal and the HLR.
3. Subscriber data from the HLR is inserted into the SGSN and the
MSC/VLR.
4. The SGSN informs the terminal that it is attached to the network.
The disconnection from the GPRS network is called GPRS detach. It can be
initiated by the mobile station or by the network (SGSN or HLR)
45
GPRS:
GPRS: PDP
PDP Context
Context Activation
Activation II
?
Después de haber efectuado el GPRS attach, si una estación
móvil quiere comunicarse con una red de datos (PDN) ?
activación de un contexto PDP.
?
?
?
Se especifican las características de la conexión: tipo de red (IP, X.25),
APN (Access Point Name), tipo de PDP (IPv4, IPv6), dirección IP
asignada a la MS, calidad de servicio requerida (QoS), etc.
El SGSN debe determinar, a partir del APN, cual es la dirección IP del
GGSN que proporciona dicho servicio.
Proceso de autenticación del usuario, generado por el GGSN.
46
To exchange data packets with external PDNs after a successful GPRS
attach, the MS must apply for the activation of packet data protocol (PDP)
context and have at least one address used in the PDN. This address is called
a PDP address and it can be static or dynamic. A static PDP address is a
permanent address that identifies a MS. A dynamic PDP address is allocated
to a MS during the PDP context activation and it is used whereas the session
is active. After that, when the MS disconnects from the GPRS network, the
PDP address will be released.
This context is stored in the MS, the SGSN, and the GGSN. With an active
PDP context, the mobile station is “visible” for the external PDN and is able
to send and receive data packets.The mapping between the two addresses,
PDP and IMSI, enables the GGSN to transfer data packets between a PDN
and MS.
After the activation of the PDP context, communication between the user
and the external packet data network can commence. The disconnection
from the GPRS network is called GPRS detach and can be initiated by the
MS or by the network (SGSN, HLR).
46
GPRS:
GPRS: PDP
PDP Context
Context Activation
Activation II
II
MS
BTS
BSC
SGSN
RADIUS
1
1
GPRS
Backbone
4
DNS
2, 3
HLR
Internet
4
GGSN
Radius client
5
Corporate
network
(1) – La MS solicita la activación de un contexto PDP (tipo de red y de PDP, APN, QoS,...).
(2) - El SGSN valida la petición basándose en los datos recibidos del HLR durante el GPRS attach.
(3) – El APN es enviado al Servidor de Nombres de Dominio (DNS) del SGSN para obtener la
dirección del GGSN más apropiado para conectar la MS con esa PDN.
(4) – Se establece una conexión lógica (tunel GTP) entre el SGSN y el GGSN. Se autentica al
usuario (el GGSN actua como cliente RADIUS). La autenticación puede ser local o delegada.
(5) – Si la MS no tiene una dirección IP fija, el GGSN le asigna una dirección IP del rango de
47
direcciones de la PDN (Internet, intranet) a la que el usuario quiere conectarse.
The process of PDP context activation consist on the following steps:
The PDP context activation procedure starts with the message “activate PDP
context request,” that the MS sends to the SGSN. If dynamic PDP address
assignment is requested, the parameter PDP address will be left empty.
Afterward, usual security functions (e.g., authentication of the user) are
performed. If access is granted, the SGSN will send a “create PDP context
request” message to the affected GGSN. The latter creates a new entry in its
PDP context table, which enables the GGSN to route data packets between
the SGSN and the external PDN. Afterward, the GGSN returns a
confirmation message “create PDP context response” to the SGSN, which
contains the PDP address in case dynamic PDP address allocation was
requested. The SGSN updates its PDP context to able and confirms the
activation of the new PDP context to the MS (“activate PDP context
accept”).
It should be stressed that, if necessary, the GGSN assigns a dynamic IP
address to the MS either from the range of IP addresses allocated to the
PLMN or externally, from a Remote Authentication Dial- in User Service
(RADIUS) server. A RADIUS server purposes are to authenticate a user and
to allocate dynamic IP addresses. A RADIUS client is included in the
GGSN to support authentication to external networks with RADIUS servers.
47
GPRS: Dynamic PDP Address Allocation I
Autenticación local
RADIUS
Server
ID, Password
Intranet 1
IP address
Firewall
RADIUS
Client
Internet
GGSN
DHCP
Intranet 2
Firewall
Firewall
48
48
GPRS: Dynamic PDP Address Allocation II
Autenticación delegada
ID, Password
RADIUS
Server
Intranet 1
Firewall
IP address
RADIUS
Client
Internet
GGSN
DHCP
Firewall
RADIUS
Server
Firewall
Intranet 2
49
We already know that a GPRS network can be interconnected with IPbased packet data networks, such as the Internet or corporate intranets.
GPRS supports both IPv4 and IPv6. From outside, i.e., from an external IP
network’s point of view, the GPRS network looks like any other IP network,
and the GGSN looks like a usual IP router. Each registered user who wants
to exchange data packets with the IP network needs an IP address, as
explained earlier and in IPv4, in order to support a large number of mobile
users, it is essential to use dynamic IP address allocation.
MS dynamic addresses may be allocated either using DHCP, Radius or
GGSN local address pools.
The addresses allocated by PLMN can be assign by the GGSN itself or by a
DHCP server.The addresses allocated by PDN can be assign by a RADIUS
or by a DHCP server. A DHCP Server (Dinamic Host Configuration
Protocol) is used to dinamically assign IP addresses to different MS /
allocate Dinamic IP addresses to MSs in case the PLMN operator is also an
ISP (Internet Service Provider) or has agreements with an ISP to provide
public access to Internet. ISP is a public network with generally public
addressing (at least for entities that have to access the Internet).
A RADIUS client is included in the GGSN to support authentication to
external networks with RADIUS servers. A RADIUS server (Remote
Access Dial Up Service) purposes are to authenticate a user, to allocate
dynamic IP addresses and to provide accounting services. To protect the
PLMN from unauthorized access, some firewalls are installed betweeen th
eprivate GPRS network and the external IP networks.
49
DNS and APNs
Finding the way
50
50
GPRS: DNS nodes functions
?
The Domain Name System is a logical name to IP address
translator and vice versa.
?
It is wanted to activate a PDP context: the SGSN needs to
determine the IP address of the GGSN serving the
requested APN.
51
51
GPRS – DNS y APNs
APNs:: DNS introducción
?
?
?
?
?
Sistema jerárquico de resolución de nombres.
Las direcciones IP son difíciles de memorizar.
Los mnemónicos son mucho más apropiados y la
traducción es bidireccional:
? www.altransdb.com -> 194.30.32.151
? 194.30.32.151 -> www.altransdb.com
Varios mnemónicos pueden traducirse por una sola
dirección y varias direcciones por un solo mnemónico.
El DNS incluye más información como el responsable de
gestionar los nombres de un dominio y el responsable de
gestionar el correo.
52
52
GPRS – DNS y APNs
APNs:: DNS en GPRS
El DNS en GPRS cumple funciones adicionales:
?
En la activación de un contexto PDP:
?
?
Selección de GGSN apropiado para el servicio seleccionado.
Para ello se usa el Access Point Name (APN) como clave.
Encaminamiento para la gestión de la movilidad entre
SGSNs (nueva RA).
?
Si el nuevo SGSN está en otra PLMN, el nuevo formato a utilizar
para averiguar la dirección IP del anterior SGSN es:
RACxxx.LACyyyy.MNCzzzz.MCCwww.GPRS.
53
In PDP context activation, the SGSN uses the Access Point Name (APN) to
query the DNS and find out the IP address of the appropriate GGSN to
connect the user and the PDN. When DNS requirement succeeds, the SGSN
creates a tunnel towards the corresponding GGSN and forwards the PDP
context activation request to the GGSN. If the GGSN to be reached is in
another PLMN, the DNS roaming function of a PLMN must have to query
information from the DNS of another PLMN. Two redundant DNS servers
should be used to provide redundancy if ine of them fails and to make
possible upgrading one of them without serving interruption.
When a MS roams between two SGSNs within the same PLMN, the new
SGSN find the address of the old SGSN by the association (old RA-old
SGSN). Thus, each SGSN knows the address to every other SGSN in the
PLMN.
When a MS roams from a SGSN to a SGSN in other PLMN, the new SGSN
may not itself have access to the address to the old SGSN. Instead, the
SGSN transforms the old RA information to a logical name of the form:
- RACxxxx.LACyyyy.MNCzzzz.MCCwwww.GPRS
Where x, y, z and w are hexadecimal digits.
The SGSN may then acquire the IP address of the old SGSN from a root
DNS server that is situated within the Inter-PLMN backbone.
53
GPRS – DNS y APNs
APNs:: DNS en GPRS
El DNS en GPRS cumple funciones adicionales:
?
Resuelve los APNs y los APNs de Servicio.
? El APN sirve para establecer la conexión lógica entre una MS y
una PDN durante el establecimiento del PDP context.
?
Permite el roaming entre redes:
? Con un sistema de DNS jerárquico (DNS primario y secundario)
? Estableciendo “enlaces punto a punto”.
?
El DNS de GPRS permanece oculto a los ojos de Internet.
54
54
GPRS – DNS y APNs
APNs:: APN
?
?
?
?
El APN codifica el enrutamiento preferido por el usuario y la
red.
El control no es absoluto del usuario si no se especifica el
APN al completo.
Se ha seguido el estándar del DNS para construir la
nomenclatura.
APN básico:
? Network_id.mnc<MNC>.mcc<MCC>.gprs
? Ibm.com.mnc214.mcc03.gprs
?
Se busca una nomenclatura más fácil de recordar
? Ibm.com.airtel.es.gprs
?
Es probable que el cliente siempre teclee “ibm.com”
55
55
GPRS – DNS y APNs
APNs:: APN de Servicio
?
Consiste de una etiqueta sin “.” para distinguirlo de un
APN.
?
Ej.: Internet, que se utilizaría cuando un usuario
simplemente quiera navegar. En este caso, probablemente
sería el ISP del operador, el que proporcionase el servicio.
?
Al ser una palabra, es necesario que exista coordinación
mundial para la asignación de sentido a las etiquetas, ya
que el roaming es cada vez más común.
?
El grupo SERG (GSM MoU Association) se encarga de
gestionar la asignación.
56
56
GPRS – DNS and APNs
APNs:: Ejemplo
Visited Operator
1
BTS
BSC
2
1.
2.
3.
4.
5.
6.
7.
8.
9.
El usuario elige un APN (en este caso en el
Home Operator)
El terminal envía “ activate PDP context”
El SGSN pide la dirección IP del GGSN a
utilizar al DNS del operador visitado, utilizando
el APN como clave.
El DNS busca la dirección IP yendo al Root
DNS si fuera necesario.
El DNS obtiene la dirección IP del DNS del
Home Operator
El DNS le pide la dirección IP del GGSN
El Home DNS devuelve la dirección IP.
El DNS responde al SGSN
El SGSN crea un contexto PDP con el Home
GGSN.
SGSN
8
Visited
DNS
3
7
VISITED
PLMN
5
GGSN
BG
4
Inter-PLMN
Backbone
Internet
Root
DNS
BG
HOME
PLMN
Home
DNS
Home Operator
GGSN A
6
P
9
my.isp.com
myoperator.fi.gprs
57
57
Direccionamiento IP
58
58
GPRS – Direccionamiento IP: Problemática
?
GPRS soporta IP versión 4 e IP versión 6. Hoy día, sólo se
trabaja con IPv4.
?
Espacio de direcciones de IPv4 es un recurso limitado y
empieza a estar saturado.
?
Los usuarios de GPRS necesitan direcciones IP públicas
para navegar por Internet.
?
Las expectativas de usuarios GPRS y de usuarios de
Internet excede el espacio libre de direcciones.
59
59
GPRS – Direccionamiento IP: Problemática
?
Dirección IP asignada durante toda la vida útil del circuito
virtual permanente en GPRS.
?
Posibilidad de conexión permanente.
?
Necesidad de disminuir el número de direcciones IP
públicas asignadas a usuarios de GPRS.
60
60
GPRS – Direccionamiento IP: Tipos de
direcciones
Two types of IP Addresses- registered and private:
?
Registered
? Used on the Internet.
? Guaranteed uniqueness.
? Finite number and supply is restricted.
? Use only where necessary.
? Apply to Internet registry demonstrating high address utilisation.
61
61
GPRS – Direccionamiento IP: Tipos de
direcciones
Two types of IP Addresses- registered and private:
?
Private
? Certain ranges available for anyone to use.
? Used by most corporates.
? Not routed on the Internet.
? Over 16 millions available.
? Interwork with Internet using NAT (Network Address Translation).
62
62
GPRS – Direccionamiento IP:
InterPLMN Backbone
?
?
?
?
?
Cada nodo que tenga acceso al InterPLMN Backbone debe
tener una dirección única.
Los nodos de GPRS deben permanecer ocultos de Internet.
El uso de GTP impide la utilización de NAT (de momento).
Los nodos deben tener direcciones públicas y registradas por
si el operador quiere utilizar Internet en algún momento como
vía alternativa al InterPLMN Backbone o a un enlace directo.
La resolución final autoriza a los operadores GPRS a pedir
nuevas direcciones IP sólo si agotan aquellas de las que
disponen.
63
63
Esquema de NAT
Diagram Showing NAT in a web request & response
Web request
Web request
From 10.4.202.136
To: 193.34.122.58
From 158.230.100.101
To: 193.34.122.58
Web response
User PC
10.4.202.136
(private)
From 193.34.122.58
To: 10.4.202.136
Web response
NAT
Firewall
10.122.23.45
(private)
Private IP Addressing
From 193.34.122.58
To: 158.230.100.101
158.230.100.101
(registered)
Web Server
193.34.122.58
(registered)
Public IP Addressing
64
NAT stands for Network Address Translation.
NAT firewall is transparent to the user and to the Web Server.
Private IP addresses are: 10.X.X.X, 172.16.X.X and 192.168.X.X
64
GPRS – Direccionamiento IP: Soluciones
?
Uso de NAT para direcciones privadas.
?
Asignación de direcciones IP privadas (RFC 1918) al
mayor número posible de usuarios. Tipos de usuarios:
?
Tipos de usuarios:
? Corporativos: la dirección IP será asignada por la red de la
empresa
? Sólo WAP: dirección privada
? WAP y servicios estándar como
SMTP/POP3/IMAP4: dirección privada
Web
y
correo
vía
? Uso no-estándar: dirección pública
65
65
Soluciones (WAP)
Diagram Showing WAP user request & response
WAP
Phone
Encoded
WAP request
WAP
Gateway
(Proxy)
Encoded
WAP response
WAP request
Internet
WAP Server
WAP response
Binary WML
Format
WML Format
WAP request
WAP response
WML
Format
Local
WAP Server
66
66
Soluciones (WAP con NAT)
Diagram Showing IP Addressing Domains
WAP
Phone
Encoded
WAP request
WAP
Gateway
(Proxy)
Firewall with
NAT
Internet
WAP Server
WAP request
Encoded
WAP response
NAT
WAP response
Binary WML
Format
WAP
request
WML
Format
Local
WAP Server
Private Addressing
Registered Addressing
67
67
Ejemplo numérico
?
Operador con 8 millones de suscriptores: mínimo 2
millones conectados.
? % Corporativos = 10%
? % Wap y Wap + Web/E-mail = 80%
? % No-estándar = 10%
?
Número de direcciones públicas necesario será de
? 200000 direcciones.
?
?
Aplicando este ejemplo a los más de 500 millones de
usuarios de GSM esperados en el 2002 se necesitarían
12,5 millones de direcciones.
Aceptable y factible.
68
68
Roaming
69
In this section of the presentation, we are going to see how GPRS networks
can interwork in order to provide GPRS roaming capabilities when users
roam onto foreign networks
69
GPRS – Roaming
Roaming:: Posibles escenarios
Las redes GPRS soportan dos escenarios básicos de
roaming:
?
?
Las MS se conectan a través del VSGSN y del HGGSN.
?
Las MS se conectan a través del VSGSN y del VGGSN.
?
El GPRS attach siempre se efectúa en el VSGSN.
?
El VSGSN consulta con el HLR de la Home PLMN.
70
70
GPRS – Roaming
Roaming:: Escenario básico
BSC
MS
BSC
BTS
BTS
Inter-PLMN
GPRS backbone
SGSN
SGSN
PLMN 1
Border
Gateway
(BG)
Intra-PLMN
GPRS backbone
Border
Gateway
(BG)
PLMN 2
Intra-PLMN
GPRS backbone
SGSN
GGSN
VSGSN y HGGSN
VSGSN y VGGSN
Packet Data Network (PDN)
(e.g. Internet, intranet)
GGSN
Router
Host
Lan
71
71
GPRS – Roaming
Roaming:: Escenario completo
Operador visitado
BTS
BSC
Domain Name System
Utilizado por SGSN para
encontrar el GGSN correcto
SGSN
DNS
VISITED
Operator
PLMN
El Border Gateway
conecta ASs
BG
GGSN
FW
BTS
Inter-PLMN
Backbone
BSC
SGSN
BG
HOME
Operator
PLMN
DNS
Internet
Root
DNS
GGSN
FW
72
72
GPRS – Roaming
Roaming:: Uso del HGGSN
BSS
GGSN
FW
GGSN
FW
R
Intra-PLMN
Backbone
SGSN
DNS
BG
Internet
inter-PLMN
Backbone
BG
73
HGGSN Home GGSN
73
GPRS – Roaming
Roaming:: Uso del VGGSN
BSS
Intra-PLMN
Backbone
VSGSN
DNS
BG
GGSN FW
GGSN
FW
R
Internet
inter-PLMN
Backbone
BG
74
VGGSN Visited GGSN
74
GPRS – Roaming
Roaming:: xGSN - Selección
?
El usuario puede influenciarlo con el APN que escoja.
? Myisp.com.operator.country.gprs: escoge implícitamente el HGGSN.
? Myisp.com – APN ambiguo – Problemática asociada.
?
La suscripción en el HLR determinará en caso de
ambigüedad.
? VPLMN add allowed Yes: Puede usarse el VGGSN.
? VPLMN add allowed No: Siempre el HGGSN.
75
75
GPRS – Roaming
Roaming:: xGSN - Selección
?
Problemática con APNs ambiguos.
? Ibm.com: si yo trabajo en ibm y quiero acceder a la red corporativa,
quiero hacerla a la de mi HGGSN o a la del VGGSN.
? En el caso de ibm probablemente sea lo mismo, pero ¿ que ocurre
con otros “network id” de menor globalidad” ?
? ISPs en distintos países utilizan el mismo nombre comercial pero
son totalmente independientes.
76
76
GRPS – Roaming
Roaming:: Voluntary
selection of HGGSN
VPLMN
APN: ibm.com.mnc.789.mcc888.gprs
SGSN
DNS
Mnc123.mcc456.gprs
HPLMN
HLR
VPLMN add. allowed flag = Yes
Dns Success
DNS
Mnc789.mcc888.gprs
VGGSN
AP:ibm.com
HGGSN
AP:ibm.com
77
77
GRPS – Roaming
Roaming:: Forced selection
of HGGSN – APN ambiguous
VPLMN
APN: ibm.com
SGSN
DNS
Mnc123.mcc456.gprs
HPLMN
HLR
VPLMN add. allowed flag = No
Dns Success
DNS
Mnc789.mcc888.gprs
VGGSN
AP:ibm.com
HGGSN
AP:ibm.com
78
78
GPRS – Roaming
Roaming:: VSGSN selection (I)
VPLMN
APN: ibm.com
Dns Success
HPLMN
HLR
SGSN
DNS
Mnc123.mcc456.gprs
DNS
Mnc789.mcc888.gprs
VGGSN
AP:ibm.com
HGGSN
AP:ibm.com
79
79
GPRS – Roaming
Roaming:: VSGSN selection (II)
VPLMN
APN: ibm.com
Dns Fail
HPLMN
HLR
SGSN
DNS
Mnc123.mcc456.gprs
DNS
Mnc789.mcc888.gprs
Dns Success
VGGSN
AP:ibm.com
HGGSN
AP:ibm.com
80
80
InterPLMN Backbone
?
?
?
?
?
Cada nodo que tenga acceso al InterPLMN Backbone debe
tener una dirección única.
Los nodos de GPRS deben permanecer ocultos de Internet.
El uso de GTP impide la utilización de NAT (de momento).
Los nodos deben tener direcciones públicas y registradas por
si el operador quiere utilizar Internet en algún momento como
vía alternativa al InterPLMN Backbone o a un enlace directo.
La resolución final autoriza a los operadores GPRS a pedir
nuevas direcciones IP sólo si agotan aquellas de las que
disponen.
81
81
Seguridad
Seguridad
82
82
GPRS
GPRS -- Seguridad
Seguridad
?
Proteger los nodos del backbone IntraPLMN
? De Internet
? De otros PLMNs
?
?
?
“Proteger” a los usuarios - “Protegerse” de ellos
Colocación de Firewalls en todos los puntos de acceso
externos
Utilización de encriptación - cifrado adicionales a los del
SGSN en la conexión con otros PLMNs/ISPs/Redes
Corporativas.
? VPNs
? IPSec
?
GTP ya proporciona un nivel de seguridad al encapsular el
tráfico en el túnel.
83
83
GPRS
GPRS -- Seguridad:
Seguridad: GTP
GTP Tunnelling
Tunnelling
IP
SNDCP
SNDCP
LLC
LLC
MS
?
IP
User level IP addresses
GTP
IP
SGSN
GTP
Backbone level IP addresses
IP
GGSN
El tunel extremo-extremo aisla a los nodos de la comunicación de
los usuarios
84
84
GPRS
GPRS –
– Seguridad:
Seguridad: IPSec
IPSec
BTS
BSC
CORP.
SGSN
DNS
VISITED
Operator
PLMN
IPSEC
ISP
GGSN
BG
BTS
BSC
SGSN
FW
Inter-PLMN
Backbone
Internet
Root
DNS
HOME
Operator
PLMN
DNS
BG
GGSN
FW
85
85
Facturación
Facturación
86
86
GPRS
GPRS -- Facturación:
Facturación: Nuevo
Nuevo método
método
?
Inconvenientes de la facturación en sistemas basados en CS:
? Basada en la duración de la conexión ? inapropiado para tráfico a
ráfagas.
?
Ventajas de la facturación con PS:
? Basada en la cantidad de datos transferidos ? posibilidad de estar
“always on”.
87
87
GPRS
Facturación: Esquema
Esquema Básico
Básico
Charging gateway
SGSN
El Charging Gateway
* recibe los CDRs generados por
los xGSN
* amalgama los CDRs y produce
un formato “adecuado” para el
sistema de facturación
Operator
IP backbone
Border Gateway
Inter operator
IP network
Billing System
GGSN
Internet
88
88
GPRS
Facturación: Roaming
Roaming
El CG procesa registros de
los GSNs del VPLMN
Acuerdo en la frecuencia, el
formato y qué es cobrable
Charging gateway
Billing System
SGSN
Operator
IP backbone
Border Gateway
GGSN
Inter operator
IP network
Internet
VPLMN
89
89
Evolución a UMTS
90
90
GPRS – Evolución a UMTS
?
Amortizar las inversiones
?
Seguir un camino evolucionario y no revolucionario
?
GPRS es un buen punto de partida para la red UMTS:
reutilizacion de Core Network.
91
91
GPRS – Evolución a UMTS: Esquema sencillo
PPDN
PPDN
PSTN
GMSC
GMSC
GGSN
GGSN
MSC
MSC
SGSN
SGSN
Upgraded MSC
Network
Server
Server
GPRS Core
Network
Gb
Iu Interface
RNC
RNC
Iu
- One Logical Interface
- Two Physical Interfaces
To GSM BSS
NODE
NODE B
B
NODE
NODE B
B
UMTS RAN
92
92
Fin
93
93
Click below to find more
Mipaper at www.lcis.com.tw
Mipaper at www.lcis.com.tw

GPRS - Mipaper by lcis.com.tw

Transcripción

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