Characteristics of Communication Devices
1.Fixed and wired
2.Mobile and wired
3.Fixed and wireless
4.Mobile and wireless
Applications of Mobile and Wireless
Devices
1.Adhoc Network
2.MANET
3.VANET
Mobile and wireless Devices
1.Sensors
2.Embedded Controllers
3.Pagers
Pager
• receive only
• tiny displays
• simple text
messages
Mobile
devices
PDA
• simple graphical displays
• character recognition
• simplified WWW
Laptop
• fully functional
• standard applications
Sensors,
embedded
controllers
Mobile phones
• voice, data
• simple text displays
Palmtop
• tiny keyboard
• simple versions
of standard applications
performance
Mobile Communications:
Introduction
1.7.1
Cellular Systems
• Solves the problem of spectral congestion and user capacity.
• Offer very high capacity in a limited spectrum without major
technological changes.
• Reuse of radio channel in different cells.
• Enable a fix number of channels to serve an arbitrarily large number
of users by reusing the channel throughout the coverage region.
Network cells
2.2 Frequency Reuse
• Each cellular base station is allocated a group of radio channels within
a small geographic area called a cell.
• Neighboring cells are assigned different channel groups.
• By limiting the coverage area to within the boundary of the cell, the
channel groups may be reused to cover different cells.
• Keep interference levels within tolerable limits.
• Frequency reuse or frequency planning
•seven groups of channel from A to G
•footprint of a cell - actual radio
coverage
•omni-directional antenna v.s.
directional antenna
2.7.1 Cell Splitting
• Split congested cell into smaller cells.
– Preserve frequency reuse plan.
– Reduce transmission power.
Reduce R to R/2
microcell
Illustration of cell splitting within a 3 km by 3 km square
Sectoring
– Replacing single omni-directional antenna by several directional antennas
– Radiating within a specified sector
Satellite Systems
 Handover
 Routing
 Systems
History of satellite communication
• 1945Arthur C. Clarke publishes an essay about „Extra
Terrestrial Relays“
• 1957 first satellite SPUTNIK
• 1960first reflecting communication satellite ECHO
• 1963
first geostationary satellite SYNCOM
• 1965
first commercial geostationary satellite Satellit „Early
Bird“
(INTELSAT I): 240 duplex telephone channels
or 1 TV
channel, 1.5 years lifetime
• 1976three MARISAT satellites for maritime communication
• 1982
first mobile satellite telephone system INMARSAT-A
• 1988
first satellite system for mobile phones and data
communication INMARSAT-C
• 1993first digital satellite telephone system
• 1998
global satellite systems for small mobile phones
Applications
 Traditionally
–
–
–
–
weather satellites
radio and TV broadcast satellites
military satellites
satellites for navigation and localization (e.g., GPS)
 Telecommunication
replaced by fiber optics
– global telephone connections
– backbone for global networks
– connections for communication in remote places or underdeveloped
areas
– global mobile communication
•  satellite systems to extend cellular phone systems (e.g., GSM
or AMPS)
Classical satellite systems
Inter Satellite Link (ISL)
Mobile User
Link (MUL)
Gateway Link
(GWL)
MUL
GWL
small cells
(spotbeams)
base station
or gateway
footprint
ISDN
PSTN: Public Switched
Telephone Network
PSTN
User data
GSM
Basics
• Satellites in circular orbits
–
–
–
–
–
–
–
attractive force Fg = m g (R/r)²
centrifugal force Fc = m r ²
m: mass of the satellite
R: radius of the earth (R = 6370 km)
r: distance to the center of the earth
g: acceleration of gravity (g = 9.81 m/s²)
: angular velocity ( = 2  f, f: rotation frequency)
• Stable orbit
– Fg = Fc
2
gR
r3
2
(2 f )
Classification of Satellite Orbits
• Circular or elliptical orbit
– Circular with center at earth’s center
– Elliptical with one foci at earth’s center
• Orbit around earth in different planes
– Equatorial orbit above earth’s equator
– Polar orbit passes over both poles
– Other orbits referred to as inclined orbits
• Altitude of satellites
– Geostationary orbit (GEO)
– Medium earth orbit (MEO)
– Low earth orbit (LEO)
Satellite Orbits
• Equatorial
• Inclined
• Polar
How it is…
• Gravity depends on the mass of the earth, the mass of the
satellite, and the distance between the center of the earth
and the satellite
• For a satellite traveling in a circle, the speed of the satellite
and the radius of the circle determine the force (of gravity)
needed to maintain the orbit
• The radius of the orbit is also the distance from the center of
the earth.
• For each orbit the amount of gravity available is therefore
fixed
• That in turn means that the speed at which the satellite
travels is determined by the orbit
Using Physics Concept…
• From what we have deduced so far, there has to be an
equation that relates the orbit and the speed of the
satellite:
r3
T  2
4 1014
R^3=mu/n^2
N=2pi/T
T is the time for one full revolution around the orbit, in seconds
r is the radius of the orbit, in meters, including the radius of the
earth (6.38x106m).
The Most Common Example
• “Height” of the orbit = 22,300 mile
• That is 36,000km = 3.6x107m
• The radius of the orbit is
3.6x107m + 6.38x106m = 4.2x107m
• Put that into the formula and …
The Geosynchronous Orbit
•
•
•
•
The answer is T = 86,000 sec (rounded)
86,000 sec = 1,433 min = 24hours (rounded)
The satellite needs 1 day to complete an orbit
Since the earth turns once per day, the
satellite moves with the surface of the earth.
• How long does a Low Earth Orbit Satellite need
for one orbit at a height of 200miles = 322km =
3.22x105m
• Do this:
– Add the radius of the earth, 6.38x106m
– Compute T from the formula
– Change T to minutes or hours
r3
T  2
4 1014
Classical satellite systems
Inter Satellite Link
(ISL)
Mobile User
Link (MUL)
Gateway Link
(GWL)
MUL
GWL
small cells
(spotbeams)
base station
or gateway
footprint
ISDN
PSTN: Public Switched
Telephone Network
PSTN
User data
GSM
Basics
• Satellites in circular orbits
– attractive force Fg = m g (R/r)²
– centrifugal force Fc = m r ²
– m: mass of the satellite
– R: radius of the earth (R = 6370 km)
– r: distance to the center of the earth
– g: acceleration of gravity (g = 9.81 m/s²)
– : angular velocity ( = 2  f, f: rotation frequency)
• Stable orbit
2
– Fg = Fc
gR
r3
(2 f )
2
Satellite period and orbits
Velocity
Km/sec
12
satellite
period [h] 24
velocity [ x1000 km/h]
20
10
16
8
12
6
8
4
4
2
synchronous distance
35,786 km
10
20
30
radius
40 x106 m
Basics
•
•
•
•
•
elliptical or circular orbits
complete rotation time depends on distance satellite-earth
inclination: angle between orbit and equator
elevation: angle between satellite and horizon
LOS (Line of Sight) to the satellite necessary for connection
 high elevation needed, less absorption due to e.g. buildings
• Uplink: connection base station - satellite
• Downlink: connection satellite - base station
• typically separated frequencies for uplink and downlink
– transponder used for sending/receiving and shifting of frequencies
– transparent transponder: only shift of frequencies
– regenerative transponder: additionally signal regeneration
Inclination
plane of satellite orbit
satellite orbit
perigee
d
inclination d
equatorial plane
Elevation
Elevation:
angle e between center of satellite beam
and surface
minimal elevation:
elevation needed at least
to communicate with the satellite
e
Orbits I
• Four different types of satellite orbits can be identified
depending on the shape and diameter of the orbit:
• GEO: geostationary orbit, ca. 36000 km above earth surface
• LEO (Low Earth Orbit): ca. 500 - 1500 km
• MEO (Medium Earth Orbit) or ICO (Intermediate Circular
Orbit): ca. 6000 - 20000 km
• HEO (Highly Elliptical Orbit) elliptical orbits
Orbits II
GEO (Inmarsat)
HEO
MEO (ICO)
LEO
(Globalstar,
Irdium)
inner and outer Van
Allen belts
earth
Van-Allen-Belts:
ionized particles
2000 - 6000 km and
15000 - 30000 km
above earth surface
1000
10000
35768
km
Geostationary satellites
• Orbit 35,786 km distance to earth surface, orbit in equatorial plane
(inclination 0°)
•  complete rotation exactly one day, satellite is synchronous to
earth rotation
• fix antenna positions, no adjusting necessary
• satellites typically have a large footprint (up to 34% of earth
surface!), therefore difficult to reuse frequencies
• bad elevations in areas with latitude above 60° due to fixed position
above the equator
• high transmit power needed
• high latency due to long distance (ca. 275 ms)
•  not useful for global coverage for small mobile phones and
data transmission, typically used for radio and TV transmission
LEO systems
•
•
•
•
•
•
•
•
•
•
•
Orbit ca. 500 - 1500 km above earth surface
visibility of a satellite ca. 10 - 40 minutes
global radio coverage possible
latency comparable with terrestrial long distance
connections, ca. 5 - 10 ms
smaller footprints, better frequency reuse
but now handover necessary from one satellite to another
many satellites necessary for global coverage
more complex systems due to moving satellites
Examples:
Iridium (start 1998, 66 satellites)
– Bankruptcy in 2000, deal with US DoD (free use,
saving from “deorbiting”)
Globalstar (start 1999, 48 satellites)
– Not many customers (2001: 44000), low stand-by times for mobiles
MEO systems
•
•
•
•
•
•
•
•
•
Orbit ca. 5000 - 12000 km above earth surface
comparison with LEO systems:
slower moving satellites
less satellites needed
simpler system design
for many connections no hand-over needed
higher latency, ca. 70 - 80 ms
higher sending power needed
special antennas for small footprints needed
•
•
Example:
ICO (Intermediate Circular Orbit, Inmarsat) start ca. 2000
– Bankruptcy, planned joint ventures with Teledesic, Ellipso – cancelled again,
start planned for 2003
Routing
•
•
•
•
•
•
•
•
•
•
•
One solution: inter satellite links (ISL)
reduced number of gateways needed
forward connections or data packets within the satellite network as long as possible
only one uplink and one downlink per direction needed for the connection of two
mobile phones
Problems:
more complex focusing of antennas between satellites
high system complexity due to moving routers
higher fuel consumption
thus shorter lifetime
Iridium and Teledesic planned with ISL
Other systems use gateways and additionally terrestrial networks
Localization of mobile stations
•
•
•
•
Mechanisms similar to GSM
Gateways maintain registers with user data
– HLR (Home Location Register): static user data
– VLR (Visitor Location Register): (last known) location of the mobile station
– SUMR (Satellite User Mapping Register):
• satellite assigned to a mobile station
• positions of all satellites
Registration of mobile stations
– Localization of the mobile station via the satellite’s position
– requesting user data from HLR
– updating VLR and SUMR
Calling a mobile station
– localization using HLR/VLR similar to GSM
– connection setup using the appropriate satellite
Handover in satellite systems
•
Several additional situations for handover in satellite systems compared to cellular
terrestrial mobile phone networks caused by the movement of the satellites
– Intra satellite handover
• handover from one spot beam to another
• mobile station still in the footprint of the satellite, but in another cell
– Inter satellite handover
• handover from one satellite to another satellite
• mobile station leaves the footprint of one satellite
– Gateway handover
• Handover from one gateway to another
• mobile station still in the footprint of a satellite, but gateway leaves the
footprint
– Inter system handover
• Handover from the satellite network to a terrestrial cellular network
• mobile station can reach a terrestrial network again which might be cheaper,
has a lower latency etc.
Overview of LEO/MEO systems
# satellites
altitude
(km)
coverage
min.
elevation
frequencies
[GHz
(circa)]
access
method
ISL
bit rate
# channels
Lifetime
[years]
cost
estimation
Iridium
66 + 6
780
Globalstar
48 + 4
1414
ICO
10 + 2
10390
Teledesic
288
ca. 700
global
8°
70° latitude
20°
global
20°
global
40°
1.6 MS
29.2 
19.5 
23.3 ISL
FDMA/TDMA
1.6 MS 
2.5 MS 
5.1 
6.9 
CDMA
2 MS 
2.2 MS 
5.2 
7
FDMA/TDMA
19 
28.8 
62 ISL
yes
2.4 kbit/s
no
9.6 kbit/s
no
4.8 kbit/s
4000
5-8
2700
7.5
4500
12
yes
64 Mbit/s 
2/64 Mbit/s 
2500
10
4.4 B$
2.9 B$
4.5 B$
9 B$
FDMA/TDMA
Definition of terms for earth-orbiting
satellite
•
•
•
•
•
•
•
•
•
Apogee The point farthest from earth. Apogee
height is shown as ha in Fig
Perigee The point of closest approach to earth.
The perigee height is shown as hp
Line of apsides The line joining the perigee and
apogee through the center of the earth.
Ascending node The point where the orbit crosses
the equatorial plane going from south to north.
Descending node The point where the orbit
crosses the equatorial plane going from north to
south.
Line of nodes The line joining the ascending and
descending nodes through the center of the earth.
Inclination The angle between the orbital plane
and the earth’s equatorial plane. It is measured at
the ascending node from the equator to the orbit,
going from east to north. The inclination is shown
as i in Fig.
Mean anomaly M gives an average value of the
angular position of the satellite with reference to
the perigee.
True anomaly is the angle from perigee to the
satellite position, measured at the earth’s center.
This gives the true angular position of the satellite
in the orbit as a function of time.
Definition of terms for
earth-orbiting satellite
•
•
•
•
Prograde orbit An orbit in which the satellite moves in the
same direction as the earth’s rotation. The inclination of a
prograde orbit always lies between 0 and 90°.
Retrograde orbit An orbit in which the satellite moves in a
direction counter to the earth’s rotation. The inclination of a
retrograde orbit always lies between 90 and 180°.
Argument of perigee The angle from ascending node to
perigee, measured in the orbital plane at the earth’s center,
in the direction of satellite motion.
Right ascension of the ascending node To define completely
the position of the orbit in space, the position of the
ascending node is specified. However, because the earth
spins, while the orbital plane remains stationary the
longitude of the ascending node is not fixed, and it cannot be
used as an absolute reference. For the practical
determination of an orbit, the longitude and time of crossing
of the ascending node are frequently used. However, for an
absolute measurement, a fixed reference in space is
required. The reference chosen is the first point of Aries,
otherwise known as the vernal, or spring, equinox. The
vernal equinox occurs when the sun crosses the equator
going from south to north, and an imaginary line drawn from
this equatorial crossing through the center of the sun points
to the first point of Aries (symbol ). This is the line of Aries.
Six Orbital Elements
• Earth-orbiting artificial satellites are defined by six orbital elements
referred to as the keplerian element set.
• The semimajor axis a.
• The eccentricity e
– give the shape of the ellipse.
• A third, the mean anomaly M, gives the position of the satellite in its orbit
at a reference time known as the epoch.
• A fourth, the argument of perigee  , gives the rotation of the orbit’s
perigee point relative to the orbit’s line of nodes in the earth’s equatorial
plane.
• The inclination I
• The right ascension of the ascending node 
– Relate the orbital plane’s position to the earth.
GPRS
• GPRS (General Packet Radio Service) is an overlay on
top of the GSM physical layer and network entities.
• Advantages:
– Short access time to the network for independent
short packets (500-1000 bytes).
– No hardware changes to the BTS/BSC
– Easy to scale
– Support for voice/data and data only terminals
– High throughput (up to 21.4 kbps)
– User friendly billing
46
GPRS
• It uses exactly the same physical radio channels as
GSM, only logical GPRS radio channels are defined.
• Allocation of the channels is flexible: from one to
eight radio interface timeslots can be allocated per
TDMA frame.
• The active users SHARE timeslots, and uplink and
downlink are allocated separately.
• The capacity allocation for GPRS is based on the actual
need for packet transfer.
• GPRS does not require permanently allocated physical
channels.
• GPRS offers permanent connections to the Internet
with volume based charging.
47
GPRS Mobile Terminal Types
– Class A Terminals
operate GPRS and other GSM services
simultaneously.
– Class B Terminals
can monitor all services, but operate either
GPRS or another service, such as GSM, one at a
time.
– Class C Terminals
operate only GPRS service.
48
GPRS Network Services
• Point-to-Multipoint (PTM-M):
Multicast service to all subscribers in a given area.
• Point-to-multipoint (PTM-G):
Multicast service to pre-determined group that may be
dispersed over a geographic area.
• Point-to-Point (PTP): Packet data transfer:
– Connectionless based on IP and CLNS called PTP-CLNS.
– Connection-oriented based on X.25 (PTP-CONS).
• Also provides a bearer service for GSM’s SMS.
49
GPRS Network Services
• GPRS has parameters that specify a QoS based on
precedence, a priority of a service in relation to
another service (high, normal, and low), reliability
and transmission characteristics required.
• Three reliability cases are defined and four delay
classes (end-to-end delay between the mobile
terminals and the interface to the network
external to GPRS).
50
GPRS Reliability Classes
Reliability Classes
Probability for
Class
Lost Packet
Duplicated
Packet
Out-of-Sequence
Packet
Corrupted
Packet
1
10-9
10-9
10-9
10-9
2
10-4
10-5
10-5
10-6
3
10-2
10-5
10-5
10-2
51
GPRS Delay Classes
Delay Classes
128 Byte Packet
1,024 Byte Packet
Class
Mean
Delay
95%
Delay
Mean
Delay
95%
Delay
1
< 0.5s
< 1.5s
< 2s
< 7s
2
< 5s
< 25s
< 15s
< 75s
3
< 50s
< 250s
< 75s
< 375s
4
Best
Effort
Best
Effort
Best
Effort
Best
Effort
52
Architecture in GPRS
53
GPRS - Network Architecture
Internet or
other networks
HLR
SGSN
MSC/
VLR
GGSN
Gateway GSN = packet switch
interworks with other networks
SGSN
Serving GPRS support node
= packet switch with mobility
management capabilities
BSC/PCU
GPRS makes use of existing
GSM base stations
54
Reference Architecture in GPRS
• There are a few new network entities called GPRS Support Nodes (GSN)
– Responsible for delivery and routing of data packets between the
mobile terminals and the external packet network.
• Two types of GSN:
– Serving GPRS Support Node (SGSN):
• Router similar to the foreign agent in Mobile IP.
• It controls access to the mobile terminals that may be attached to
a group of BSCs. This is called a routing area or a service area of
the SGSN.
• Responsible for delivery of packets to the mobile terminal in the
service area and from the mobile terminal to the Internet.
• It also performs logical link management, authentication, and
charging functions.
55
Reference Architecture in GPRS
– Gateway GPRS Support Node (GGSN):
• Acts as a logical interface to the Internet.
• It maintains routing information so that it can route
the packets to the SGSN servicing the mobile terminal.
• It analyzes the PDN address of the mobile terminal
and converts it to the corresponding IMSI and is
equivalent to the HA in Mobile IP.
56
Reference Architecture in GPRS
• New database: GPRS register (GR), colocated with the HLR. It
stores routing information and maps the IMSI to PDN address
(IP address, for example).
• Um interface is the air-interface and connects the MS to the
BSS.
• The interface between the BSS and the SGSN is called Gb.
• The interface between the SGSN and the GGSN is called the Gn
interface.
57
GPRS Interfaces
58
Mobility Support in GPRS
• Attachment Procedure:
– Before accessing GPRS services, the MN must
register with the GPRS network and become
“known” to the PDN.
– The MS performs an “attachment procedure” with
an SGSN that includes authentication (checking
with the GR).
– The MS is allocated a temporary logical link
identifier (TLLI) by the SGSN and a PDP (packet
data protocol) context is created for the MS.
59
Mobility Support in GPRS
• This context is a set of parameters created for each
session and contains the PDP type, such as IPv4, the PDP
address assigned to the MS, the requested QoS
parameters, and the GGSN address that serves the
point of access to the PDN.
• The PDN context is stored in the MS, the SGSN, and
the GGSN.
• A user may have several PDP contexts enabled at a time.
• The PDP address may be statically or dynamically
assigned (static address is most common).
• The PDP context is used to route packets accordingly.
60
Location and Handoff Management in
GPRS
• Based on keeping track of the MSs location and
having the ability to route packets to it accordingly.
• The SGSN and GGSN play the role of foreign and
HA, respectively, as in Mobile IP.
• There are three states in which the MS can be:
– IDLE state – the MS is not reachable, and all PDP
contexts are deleted
– STANDBY state – movement across routing areas
is updated to the SGSN but not across cells.
– READY state – every movement of the MS is
indicated to the SGSN.
61
Location and Handoff Management in
GPRS
• The reason for the three states approach:
– If the MS updates its location too often, it
consumes battery power and wastes the
air-interface resources.
– If the update is too rare, a system wide
paging is needed: again waste of resources.
62
Location Management in GPRS
•
During the STANDBY state there are two
types of routing area updates:
– Intra-SGSN RA update
• The SGSN already has the user
profile and PDP context.
• A new temporary mobile
subscriber identity is issued as
part of routing area update
“accept”.
• The HLR need not be updated.
– Inter-SGSN RA update
• The new RA is serviced by a new
SGSN.
• The new SGSN requests the old
SGSN to send the PDP contexts
of the MS.
• The new SGSN informs the home
GGSN, the GR, and other GGSNs
about the user’s new routing
context.
63
Location and Handoff Management in
GPRS
• Mobility management in GPRS starts at handoff
initiation.
• The MS listens to the BCCH and decides which cell
it has to select.
• The MS measures the RSS of the current BCCH
and compares it with the RSS of the BCCH of the
adjacent cells and decides on which cell to attach
it to.
• There is an option for handoff similar to GSM
(MAHO).
• Handoff procedure is very similar to mobile IP.
64
Location and Handoff Management in
GPRS
The location is updated with a routing update procedure:
1. When an MS changes a routing area (RA), it sends
an RA update request containing cell identity and the
identity of the previous routing area, to the new SGSN.
2.The new SGSN asks the old SGSN to provide the
routing context (GGSN address and tunneling
information) of the MS.
3. The new SGSN then updates the GGSN of the home
network with the new SGSN address and new tunneling
information. It also updates the HLR.
– The HLR cancels the MS information context in the old SGSN and
loads the subscriber data to the new SGSN.
The new SGSN acknowledges the MS.
– The previous SGSN is requested to transmit undelivered data to the
new SGSN.
65
Location and Handoff
Management in GPRS
66
Short Messaging Service (SMS)
• Users of SMS can exchange
alphanumeric messages of up to 160
characters.
• Service is available wherever GSM
exists making it a very attractive wide
area data service.
67
Short Messaging Service (SMS)
• Uses the same network entities as GSM (with the
addition of the SMS center – SMSC), the same
physical layer, and intelligently reuses the logical
channels of the GSM system to transmit messages.
• It has an almost instant delivery if the destination
MS is active.
• It supports a store-and-forward delivery if the MS
is inactive.
68
Short Messaging Service (SMS)
• Two types of services:
– Cell broadcast service – message is
transmitted to all MSs that are active in a cell
and that are subscribed to the service
(unconfirmed, one-way message).
• Used to send weather forecast, stock quotes,
game scores, and so on,
– PTP service – MS sends a message to another
MS using a handset keypad, a PDA or a laptop
connected to the handset, or by calling a
paging center.
69
Short Messaging Service (SMS)
• A short message (SM) can have a certain priority,
future delivery time, expiration time, or it might be
one of several predefined messages.
• A sender may request an acknowledgement of
message receipt.
• A recipient can manually acknowledge message or
have predefined messages for acknowledgement.
• A SM will be delivered and acknowledged whether a
call is in progress.
70
Short Messaging Service (SMS)
• Each message is maintained and
transmitted by the SMSC.
• The SMSC sorts and routes the
messages appropriately.
• The SM are transmitted through the
GSM architecture using SS-7.
71
Short Messaging Service (SMS)
•
•
Mobile Originated Short Message:
– SM is first delivered to a service center.
– Before that, it reaches an MSC for processing.
• A dedicated function called SMS-interworking MSC (SMSIWMSC) allows the forwarding of the SM to the SMSC using a
global SMSC ID.
Mobile Terminated Short Message:
– It is forwarded by the SMSC to the SMS-gateway MSC (SMSGMSC) function in a MSC.
• It either queries the HLR or sends it to the SMS-GMSC
function at the home MSC of the recipient.
– Subsequently, the SM is forwarded to the appropriate MSC, and it
delivers the message to the MS.
• It queries the VLR for details about the location of the MS, the
BSC controlling the BTS providing coverage to the MS, and so
on.
72
Short Messaging Service (SMS)
• SMs are transmitted in time slots that are freed up in the
control channels.
• If the MS is in idle state, the short messages are sent over the
SDCCH at 184 bits within approximately 240 ms.
• If the MS is the active state (handling a call), the SDCCH is
used for call setup and maintenance.
– The SACCH is used for delivery at around 168 bits every 480
ms.
• Failures can occur is there is state change when the SM is in
transit. The SM will have to be transmitted later.
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General Packet Radio Service
• General packet radio service (GPRS) is a packet oriented mobile
data service
• on the 2G and 3G cellular communication system's global system
for mobile communications
• (GSM).
• GPRS was originally standardized by European
Telecommunications Standards Institute (ETSI)
• in response to the earlier CDPD and i-mode packet-switched
cellular technologies.
•
It is now maintained by the 3rd Generation Partnership Project
(3GPP).
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• GPRS usage is typically charged based on volume of data
transferred, contrasting with circuit switched data, which is
usually billed per minute of connection time.
• Usage above the bundle cap is either charged per megabyte or
disallowed.
• 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.
• In 2G systems, GPRS provides data rates of 56–114
kbit/second.
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• GPRS is integrated into GSM Release 97 and newer releases.
• The GPRS core network allows 2G, 3G 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.
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• Services offered
• GPRS extends the GSM Packet circuit switched data capabilities
and makes the following services possible:
SMS messaging and broadcasting
"Always on" internet access
Multimedia messaging service (MMS)
Push to talk over cellular (PoC)
Instant messaging and presence—wireless village
Internet applications for smart devices through wireless
application protocol (WAP)
•
Point-to-point (P2P) service: inter-networking with the
Internet (IP)
•
Point-to-Multipoint (P2M) service:point-to-multipoint
multicast and point-to-multipoint group calls
•
•
•
•
•
•
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• If SMS over GPRS is used, an SMS transmission speed of
about 30 SMS messages per minute may be achieved.
• This is much faster than using the ordinary SMS over GSM,
• whose SMS transmission speed is about 6 to 10 SMS
messages per minute.
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• Protocols supported
• GPRS supports the following protocols:
Internet protocol (IP). In practice, built-in mobile browsers
use IPv4 since IPv6 was
• 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.
•
• This allows an IP address to be assigned dynamically (IPCP not
DHCP) to the mobile equipment.
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•
•
•
•
Protocols supported
X.25 connections.
This is typically used for applications like wireless payment
terminals, although it has been removed from the standard.
• X.25 can still be supported over PPP, or even over IP, but doing
this requires either a network-based router to perform
encapsulation or intelligence
• built into the end-device/terminal; e.g., user equipment (UE).
• TCP/IP
• 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).
• .
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• Hardware
• Devices supporting GPRS are divided into three classes:
• Class A
•
Can be connected to GPRS service and GSM service (voice,
SMS), using both at the same time. Such devices are known to
be available today.
• Class B
•
Can be connected to GPRS service and GSM service (voice,
SMS), but using only one or the other at a given time. During
GSM service (voice call or SMS), GPRS service is suspended, and
then resumed automatically after the GSM service (voice call or
SMS) has concluded. Most GPRS mobile devices are Class B.
• Class C
•
Are connected to either GPRS service or GSM service (voice,
SMS). Must be switched manually between one or the other
service.
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• GPRS - Architecture
• GPRS architecture works on the same procedure like GSM
network.
• but, has additional entities that allow packet data transmission.
• This data network overlaps a second-generation GSM network
providing packet data transport at the rates from 9.6 to 171
kbps.
•
Along with the packet data transport the GSM network
accommodates multiple users to share the same air interface
resources concurrently.
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• GPRS attempts to reuse the existing GSM network elements as much as
possible.
•
but to effectively build a packet-based mobile cellular network, some
new network elements, interfaces, and protocols for handling packet
traffic are required.
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• 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 and
Serving GPRS support node.
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• Gateway GPRS support node (GGSN)
• The gateway GPRS support node (GGSN) is a main component of
the GPRS network.
• The GGSN is responsible for the internetworking between the
GPRS network and
• external packet switched networks, like the Internet and X.25
networks.
• 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.
• When the GGSN receives data addressed to a specific user, it
checks if the user
• is active. If it is, the GGSN forwards the data to the SGSN
serving the mobile user,
• but if the mobile user is inactive, the data is discarded.
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• Gateway GPRS support node (GGSN)
• The GGSN is the anchor point that enables the mobility of the
user terminal in the GPRS/UMTS networks.
• In essence, it carries out the role in GPRS equivalent to the
home agent in Mobile IP.
•
It maintains routing necessary to tunnel the protocol data units
(PDUs) to the SGSN that services a particular MS (mobile
station).
• The GGSN 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.
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• Gateway GPRS support node (GGSN)
• 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.
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• Gateway GPRS support node (GGSN)
• 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.
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