Characteristics of Communication Devices 1.Fixed and wired 2.Mobile and wired 3.Fixed and wireless 4.Mobile and wireless

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 Devices1.Adhoc Network

2.MANET

3.VANET

Mobile and wireless Devices

1.Sensors

2.Embedded Controllers

3.Pagers

Mobile Communications: Introduction

Mobile devices

performance

Pager• receive only• tiny displays• simple text messages

Mobile phones• voice, data• simple text displays

PDA• simple graphical displays• character recognition• simplified WWW

Palmtop• tiny keyboard• simple versions of standard applications

Laptop• fully functional• standard applications

1.7.1

Sensors,embeddedcontrollers

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.

microcell

Reduce R to R/2

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

• 1945 Arthur C. Clarke publishes an essay about „Extra Terrestrial Relays“

• 1957 first satellite SPUTNIK• 1960 first 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

• 1976 three 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• 1993 first 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– 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)

replaced by fiber optics

base stationor gateway

Classical satellite systemsInter Satellite Link (ISL)

Mobile User Link (MUL) Gateway Link

(GWL)

footprint

small cells (spotbeams)

User data

PSTNISDN GSM

GWL

MUL

PSTN: Public Switched Telephone Network

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 3

2

2

)2( f

gRr

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:

T 2r3

4 1014

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).

R^3=mu/n^2

N=2pi/T

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

T 2r3

4 1014

base stationor gateway

Classical satellite systems

Inter Satellite Link (ISL)

Mobile User Link (MUL) Gateway Link

(GWL)

footprint

small cells (spotbeams)

User data

PSTNISDN GSM

GWL

MUL

PSTN: Public Switched Telephone Network

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

32

2

)2( f

gRr

Satellite period and orbits

10 20 30 40 x106 m

24

20

16

12

8

4

radius

satellite period [h]

velocity [ x1000 km/h]

synchronous distance35,786 km

12

10

8

6

4

2

VelocityKm/sec

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

inclination d

d

satellite orbit

perigee

plane of satellite orbit

equatorial plane

Elevation

Elevation:angle e between center of satellite beam and surface

eminimal elevation:elevation needed at leastto communicate with the satellite

footprint

• 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 I

Orbits II

earth

km35768

10000

1000

LEO (Globalstar,

Irdium)

HEO

inner and outer VanAllen belts

MEO (ICO)

GEO (Inmarsat)

Van-Allen-Belts:ionized particles2000 - 6000 km and15000 - 30000 kmabove earth surface

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 systemsIridium Globalstar ICO Teledesic

# satellites 66 + 6 48 + 4 10 + 2 288altitude(km)

780 1414 10390 ca. 700

coverage global 70° latitude global globalmin.elevation

8° 20° 20° 40°

frequencies[GHz(circa)]

1.6 MS29.2 19.5 23.3 ISL

1.6 MS

2.5 MS 5.1

6.9

2 MS

2.2 MS 5.2

7

19

28.8 62 ISL

accessmethod

FDMA/TDMA CDMA FDMA/TDMA FDMA/TDMA

ISL yes no no yesbit rate 2.4 kbit/s 9.6 kbit/s 4.8 kbit/s 64 Mbit/s

2/64 Mbit/s # channels 4000 2700 4500 2500Lifetime[years]

5-8 7.5 12 10

costestimation

4.4 B$ 2.9 B$ 4.5 B$ 9 B$

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.

• 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.

Definition of terms for earth-orbiting satellite

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.

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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

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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.

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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.

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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.

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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).

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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

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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

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Architecture in GPRS

54

GPRS - Network Architecture

GPRS makes use of existing GSM base stations

Serving GPRS support node = packet switch with mobility management capabilities

Gateway GSN = packet switch interworks with other networks

Internet or other networks

GGSNMSC/VLR

SGSN SGSN

HLR

BSC/PCU

55

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.

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– 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.

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• 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.

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GPRS Interfaces

59

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.

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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.

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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.

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• 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.

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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.

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• 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.

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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.

66


67

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.

68


• 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.

69


• 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.

70


• 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.

71


• 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.

72


• 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 (SMS-IWMSC) 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 (SMS-

GMSC) 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.

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• 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.

76

• 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

78

• 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.

79

• 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.

83

• 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.

84

85

• 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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• 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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• 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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• 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.

Documents

Characteristics of Communication Devices 1.Fixed and wired 2.Mobile and wired 3.Fixed and wireless 4.Mobile and wireless