GPRS Core Network - CSIS

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12 Δεκ 2013 (πριν από 3 χρόνια και 7 μήνες)

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3G System



What is 3G


3
G

or

3
rd

generation

mobile

telecommunications

is

a

generation

of

standards

for

mobile

phones

and

mobile

telecommunication

services

fulfilling

the

International

Mobile

Telecommunications
-
2000

(IMT
-
2000
)

specifications

by

the

International

Telecommunication

Union
.


Application

services

include

wide
-
area

wireless

voice

telephone,

mobile

Internet

access,

video

calls

and

mobile

TV,

all

in

a

mobile

environment
.



To

meet

the

IMT
-
2000

standards,

a

system

is

required

to

provide

peak

data

rates

of

at

least

200

kbit/s
.



The following standards are typically branded 3G:



the UMTS system
, first offered in 2001, standardized by 3GPP, used
primarily in Europe, Japan, China (however with a different radio interface)
and other regions predominated by GSM 2G system infrastructure. The cell
phones are typically UMTS and GSM hybrids.


the

CDMA
2000

system
,

first

offered

in

2002
,

standardized

by

3
GPP
2
,

used

especially

in

North

America

and

South

Korea,

sharing

infrastructure

with

the

IS
-
95

2
G

standard
.

The

cell

phones

are

typically

CDMA
2000

and

IS
-
95

hybrids
.



3G Network




GPRS Core Network


General

packet

radio

service

(GPRS)

is

a

packet

oriented

mobile

data

service

on

the

2
G

and

3
G

cellular

communication

system's

GSM
.




GPRS

was

originally

standardized

by

European

Telecommunications

Standards

Institute

(ETSI)

and

is

now

maintained

by

the

3
rd

Generation

Partnership

Project

(
3
GPP)
.



GPRS

usage

charging

is

based

on

volume

of

data,

either

as

part

of

a

bundle

or

on

a

pay
-
as
-
you
-
use

basis
.

This

contrasts

with

circuit

switching

data,

which

is

typically

billed

per

minute

of

connection

time,

regardless

of

whether

or

not

the

user

transfers

data

during

that

period
.



GPRS

is

a

best
-
effort

service,

implying

variable

throughput

and

latency

that

depend

on

the

number

of

other

users

sharing

the

service

concurrently,

as

opposed

to

circuit

switching,

where

a

certain

quality

of

service

(QoS)

is

guaranteed

during

the

connection
.



2
.
5
G

and

3
G

systems

rely

on

double

core

network

infrastructures
;

traditional

circuit
-
switched

network

nodes

(switching

points)

for

telephony,

and

packet
-
switched

GPRS

nodes

for

various

data

services
.

Dedicated

nodes

handle

the

SMS

service
.




GPRS Core Network

GPRS

supports

the

following

protocols
:



Internet

protocol

(IP)
.

In

practice,

built
-
in

mobile

browsers

use

IPv
4

since

IPv
6

is

not

yet

popular
.


Point
-
to
-
point

protocol

(PPP)
.

In

this

mode

PPP

is

often

not

supported

by

the

mobile

phone

operator

but

if

the

mobile

is

used

as

a

modem

to

the

connected

computer,

PPP

is

used

to

tunnel

IP

to

the

phone
.



X
.
25

connections
.

This

is

typically

used

for

applications

like

wireless

payment

terminals,

although

it

has

been

removed

from

the

standard
.



When

TCP/IP

is

used,

each

phone

can

have

one

or

more

IP

addresses

allocated
.

GPRS

will

store

and

forward

the

IP

packets

to

the

phone

even

during

handover
.

The

TCP

handles

any

packet

loss

(e
.
g
.

due

to

a

radio

noise

induced

pause)
.

Addressing



A

GPRS

connection

is

established

by

reference

to

its

access

point

name

(APN)
.



The

APN

defines

the

services

such

as

WAP

access,

SMS,

MMS,

and

for

Internet

communication

services

such

as

email

and

WWW

access
.





GPRS Core Network


The

GPRS

core

network

is

the

central

part

of

the

GPRS

which

allows

2
G,

3
G

and

WCDMA

mobile

networks

to

transmit

IP

packets

to

external

networks

such

as

the

Internet
.




The

GPRS

system

is

an

integrated

part

of

the

GSM

network

switching

subsystem
.



The

GPRS

core

network

provides

mobility

management,

session

management

and

transport

for

Internet

Protocol

packet

services

in

GSM

and

WCDMA

networks
.




The

core

network

also

provides

support

for

other

additional

functions

such

as

billing
.




GPRS support nodes (GSN)


A

GSN

is

a

network

node

which

supports

the

use

of

GPRS

in

the

GSM

core

network
.



All

GSNs

should

have

a

Gn

interface

and

support

the

GPRS

tunneling

protocol
.



There

are

two

key

variants

of

the

GSN,

namely

Gateway

GPRS

Support

Node

(GGSN)

and

Serving

GPRS

Support

Node

(SGSN)
.


Gateway

GPRS

Support

Node

(GGSN)


The

GGSN

is

responsible

for

the

interworking

between

the

GPRS

network

and

external

packet

switched

networks,

like

the

Internet
.


From

an

external

network's

point

of

view,

the

GGSN

is

a

router

to

a

sub
-
network,

because

the

GGSN

‘hides’

the

GPRS

infrastructure

from

the

external

network
.



Gateway GPRS Support Node (GGSN)


The

GGSN

is

the

anchor

point

that

enables

the

mobility

of

the

user

terminal

in

the

GPRS/UMTS

networks
.




It

carries

out

the

role

in

GPRS

equivalent

to

the

Home

Agent

in

Mobile

IP
.




It

maintains

necessary

routing

information

to

tunnel

the

Protocol

Data

Units

(PDUs)

to

the

SGSN

that

service

a

particular

MS
.



The

GGSN

converts

the

GPRS

packets

coming

from

the

SGSN

into

the

appropriate

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
.




The

GGSN

is

responsible

for

IP

address

assignment

and

is

the

default

router

for

the

connected

user

equipment

(UE)
.




The

GGSN

also

performs

authentication

and

charging

functions
.


Other

functions

include

subscriber

screening,

IP

Pool

management

and

address

mapping,

QoS

and

PDP

context

enforcement
.



Serving GPRS Support Node (SGSN)


It

is

responsible

for

the

delivery

of

data

packets

from

and

to

the

mobile

stations

within

its

geographical

service

area
.



It

provides

session

management,

i
.
e
.

mechanisms

for

establishment,

maintenance,

and

release

of

end

user

PDP

contexts
.



Its

tasks

include

packet

routing

and

transfer,

mobility

management

(attach/detach

and

location

management),

logical

link

management,

and

authentication

and

charging

functions
.


It


Detunnel

GTP

packets

from

the

GGSN

(downlink)


Tunnel

IP

packets

toward

the

GGSN

(uplink)


Carry

out

mobility

management

as

Standby

mode

mobile

moves

from

one

Routing

Area

to

another

Routing

Area


Billing

user

data





GPRS
tunnelling

protocol (GTP)


GTP

is

a

group

of

IP
-
based

communications

protocols

used

to

carry

GPRS

within

GSM,

UMTS

and

LTE

networks
.


It

is

the

protocol

which

allows

end

users

of

a

GSM

or

UMTS

network

to

move

from

place

to

place

whilst

continuing

to

connect

to

the

Internet

as

if

from

one

location

at

the

GGSN
.



It

does

this

by

carrying

the

subscriber's

data

from

the

subscriber's

current

SGSN

to

the

GGSN

which

is

handling

the

subscriber's

session
.

Three

forms

of

GTP

are

used

by

the

GPRS

core

network
.


GTP
-
U

for

transfer

of

user

data

in

separated

tunnels

for

each

PDP

context
.


GTP
-
C

for

control

reasons

including
:



setup

and

deletion

of

PDP

contexts


verification

of

GSN

reachability


updates
;

e
.
g
.
,

as

subscribers

move

from

one

SGSN

to

another
.


GTP'

for

transfer

of

charging

data

from

GSNs

to

the

charging

function
.





PDP (Packet Data protocol) Context


When

a

GPRS

mobile

phone

sets

up

a

PDP

context,

the

access

point

(An

IP

network

to

which

a

mobile

can

be

connected)

is

selected
.

At

this

point

an

access

point

name

(APN)

is

determined
.


The

PDP

(e
.
g
.
,

IP,

X
.
25
,

FrameRelay)

context

is

a

data

structure

present

on

both

the

SGSN

and

the

GGSN

which

contains

the

subscriber's

session

information

when

the

subscriber

has

an

active

session
.



When

a

mobile

wants

to

use

GPRS,

it

must

first

attach

and

then

activate

a

PDP

context
.

This

allocates

a

PDP

context

data

structure

in

the

SGSN

that

the

subscriber

is

currently

visiting

and

the

GGSN

serving

the

subscriber's

access

point
.

The

data

recorded

includes
:


Subscriber's

IP

address


Subscriber's

IMSI


Subscriber's



Tunnel

Endpoint

ID

(TEID)

at

the

GGSN


Tunnel

Endpoint

ID

(TEID)

at

the

SGSN


The

Tunnel

Endpoint

ID

(TEID)

is

a

number

allocated

by

the

GSN

which

identifies

the

tunnelled

data

related

to

a

particular

PDP

context
.




3G Network







3GPP


WLAN Interworking Scenarios


3
GPP

22
.
934

specifies

six

3
GPP
-
WLAN

interworking

scenarios
.



Each

scenario

realises

an

additional

step

in

integrating

WLAN

in

the

3
GPP

service

offering

and

naturally

includes

the

previous

level

of

integration

of

the

previous

scenario
.




3
GPP

-
WLAN

interworking

scenarios

may

be

considered

with

the

aid

of

the

simplified

reference

diagram

shown

in

next

slide
.




This

reference

diagram

illustrates

the

elements

of

the

3
GPP

system

and

WLANs

being

interworked
.

These

may

be

interconnected

in

a

variety

of

ways

to

develop

the

progressive

scenarios

outlined

in

this

section






Scenario 1
-

Common Billing and
Customer Care


The

connection

between

the

WLAN

and

the

3
GPP

system

is

that

there

is

a

single

customer

relationship
.




The

customer

receives

one

bill

from

the

mobile

operator

for

the

usage

of

both

3
GPP

and

WLAN

services
.




Integrated

Customer

Care

allows

for

a

simplified

service

offering

from

both

the

operator

and

the

subscribers

perspective
.




The

security

level

of

the

two

systems

may

be

independent
.




This

scenario

does

not

pose

any

new

requirements

on

3
GPP

specifications
.



Scenario 2
-

3GPP system based Access
Control and Charging


This

is

the

scenario

where

authentication,

authorization

and

accounting

are

provided

by

the

3
GPP

system
.



The

security

level

of

these

functions

applied

to

WLAN

is

in

line

with

that

of

the

3
GPP

system
.

This

provide

means

for

the

operator

to

charge

access

in

a

consistent

manner

over

the

two

platforms
.



Benefits

of

reusing

the

3
GPP

system

access

control

principles
:




The

3
GPP

system

operator

may

easily

allow

subscribers

within

his

existing

3
GPP

system

customer

base

to

access

the

WLAN

with

a

minimum

effort

both

for

the

subscriber

and

the

operator
.



The

maintenance

of

the

subscriber

may

also

be

simplified
.




Scenario 3: Access to 3GPP system PS
based services


The

goal

of

this

scenario

is

to

allow

the

operator

to

extend

3
GPP

system

PS

based

services

to

the

WLAN
.




These

services

may

include,

for

example,

APNs,

IMS

based

services,

location

based

services,

instant

messaging,

presence

based

services

etc
.




Even

though

this

scenario

allows

access

to

all

services,

it

is

an

implementation

question

whether

only

a

subset

of

the

services

is

actually

provided
.




However,

service

continuity

between

the

3
GPP

system

part

and

the

WLAN

part

is

not

required
.




Scenario 4: Service Continuity


The

goal

of

this

scenario

is

to

allow

the

services

supported

in

Scenario

3

to

survive

a

change

of

access

between

WLAN

and

3
GPP

systems
.




The

change

of

access

may

be

noticeable

to

the

user,

but

there

will

be

no

need

for

the

user/UE

to

reestablish

the

service
.




There

may

be

a

change

in

service

quality

as

a

consequence

of

the

transition

between

systems

due

to

the

varying

capabilities

and

characteristics

of

the

access

technologies

and

their

associated

networks
.




It

is

also

possible

that

some

services

may

not

survive,

as

the

continuing

network

may

not

support

an

equivalent

service
.




Scenario 5: Seamless services


The

goal

of

this

scenario

is

to

provide

seamless

service

continuity

between

the

access

technologies,

for

the

services

supported

in

Scenario

3
.




By

seamless

service

continuity

is

meant

minimizing

aspects

such

as

data

loss

and

break

time

during

the

switch

between

access

technologies
.




Scenario 6: Access to 3GPP CS Services


This

scenario

allows

access

to

services

provided

by

the

entities

of

the

3
GPP

Circuit

Switched

Core

Network

over

WLAN
.




This

scenario

does

not

imply

any

circuit
-
switched

type

of

characteristics

to

be

included

into

WLAN
.