introduction of gprs [compatibility mode]

8/3/2019 Introduction of GPRS [Compatibility Mode]

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General Packet Radio Service(GPRS)


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wireless packet service created by ETSI

GPRS enhances the existing GSM

infrastructure b addin a acket solution thatprovides a simplified access to packetnetworks such as the Internet.

GSM + Packet Switched Services = GPRS


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Internet Services


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IWF = Interworking Function


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Limitation of Circuit SwitchedData

Motivation for GPRS contd. .


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Mobile wireless networks need to provide an Always

to wire-line and enterprise networks.Motivation for GPRS contd. .


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101010001



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Benefits to the wireless operators

spare capacity from voice can be readily availablefor data traffic



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Benefits to the wireless operators

. ..

allows the operator to get more mileage out of theirspectrum.

,operator to retain the subscriptions of current GSM

subscribers Motivation for GPRS contd. .


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Packet Solution

An Air Interface Solution: GPRS defines modifications to theexisting GSM air interface to support packet access.

: e nes a new ac e w c e - oreNetwork (PS-CN) to provide access to external packet networks for

GPRS Mobile Stations (MSs) or devices.Motivation for GPRS contd. .


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of the standard second generation GSM

A BSS consists of a BTS and a BSC.

yp ca y e a e o a wONLY software changes to the BTS and BSC

(Addition of Packet Control Unit (PCU) )only.


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Gb Interface


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Lets compare GPRS to a basic GSM circuit switchedca :

In a circuit switched call, a user is assigned resources (i.e.,frequency and timeslot combination) during the call setup, and

. This design is suitable for voice calls as the traffic is generally

continuous and symmetrical (an equal amount of data is flowing in

the uplink and the downlink). This design is an inefficient means oftransferrin acket data because it is enerall burst andasymmetrical.

GPRS extends GSM by allowing multiple users to share a singleresource. This allows the precious air interface resources to beused more efficientl . GPRS allows users to take turns sendin

and receiving data on a given time slot. This may decrease the data rates for the user, but will allow the

system to support more concurrent users.


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Air Interface Solution Contd...

(Mobile tation)

packet switched and circuit switched

Class B: MS can operate either one at

Class C: MS can operate only packet

sw c e serv ces E.g. expansion cards for laptops


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The GPRS network solution consists of a new Packet Switched-Core Network (PS-CN).

The PS-CN introduces two new nodes to coordinate acket

capabilities for GPRS mobiles. They are the Serving GPRS Support Node (SGSN) and the

Gateway GPRS Support Node (GGSN). Lets go over their roles.


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Each GPRS network contains multi le SGSNsand GGSNs based on the amount of neededpacket capacity.

private IP networks.

The GGSNs main roles include: managing IP address allocation for GPRS mobiles masking mobility of GPRS mobiles from external

networks

providing connections for mobiles to external packetnetworks or services

eneratin billin CDRs


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GPRS allows subscribers with their wireless

devices to access packet networks such as theInternet.

,GPRS need some form of address.

In the case of circuit switched data, the mobilea e n o a mo em poo an was a oca e anaddress by the Internet Service Provider.

What ha ens in the case of GPRS


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,

temporary address or a permanent address: Permanent addresses are associated with a particular

subscriber when he/she subscribes to a service andremain assigned to that user for the duration of his or

.

Permanent addresses are not very common and areexpensive to obtain.

A wireless web server is an example of an entity thatmay need a permanent address, as the server needs

.


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are associated with a particular subscriber when thatsubscriber starts a packet data session

Each time the subscriber connects to the network heor she may be assigned a new address.

,each time they connect, similar to wire-line ISPs.

A lications such as email, web access, and so on,

work well with temporary addresses.


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Another feature of GPRS is the definition of various mechanisms and,

different networks. This feature was not available in circuit switched data and has been added to

GPRS. QoS can come into la at various oints in the life of a GPRS subscriber. First,

the subscriber may choose a certain QoS as the default QoS for his account. Each time he accesses the network an attempt will be made by the network to

provide, and charge for, this subscribed QoS.


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When an attem t is made to start a acket data

session, the network must decide whether or notto accept the new session at the requested QoS.

users who are already connected to the network. Based on the results of its analysis, the network may

decide to admit the new connection with therequested QoS, offer the user a different QoS, orreject the request

QoS may still change during the connection. This may happen for a number of reasons, including

.


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This table summarizes the MAXIMUM data rates achievable with

GPRS radio systems. Two values are given one or a s ng e me s o and one for the sum of all eight time slots.

The actual data rates that end users will achieve will beSIGNIFICANTLY LOWER than these values. This is due to a

number of factors it is unlikely that an operator would allocate all eight time slots for onesubscribers use.

in a wireless medium where the air interface is error rone some formof error protection and retransmission of information is needed, which ineffect reduces the data rate available to applications.


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Since GPRS is desi ned to be an evolution of GSM

networks, the circuit switched components have notchanged

the CS-CN is named the GSM PLMN or GSM Public

Land Mobile Network and the PS-CN for GPRS is theGPRS PLMN

However, the PLMN technically refers to the operator'snetwork, including both the core network and the access


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Its primary role is to route data from the Packet Data Network to the

.the mobiles and hides the mobility of the GPRS user from the packetdata network.

There may be several GGSNs within the PLMN, and each GGSN mayhave multiple SGSNs connected to it

One GGSN ma connect to multi le external PDNs

The interconnection between the GGSN and the SGSN is an IP-basedGPRS backbone network

When required, the GGSN may interface with the HLR in order to obtainlocation information for the mobile, either directly or via the SGSNinterface.


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In order to enable traffic deliver of ackets to

and from the mobile, coordination is requiredbetween the mobile, the Serving GPRS Support

Node (GGSN)

Once this coordination is complete, packetsflowing from the mobile station must first be sent

over-the-air to the BSS. The BSS then sendsthese, along with all other packet traffic, to the

.


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. The SGSN uses its routing table or a Domain Name Server (DNS) to

determine through which GGSN the packets should travel

It wraps the packets in a forwarding header and sends them to the

When the GGSN receives them, it unwraps them and sends them

The packets are then routed to the destination like any other IP

The rest of the Internet does not know the fact that they once went.


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. Now consider traffic being sent from any host on the Internet to the

The sending-host addresses the packet to the mobile using themobiles IP address

This may be a dynamically-assigned IP address and the sendinghost must know this address before sending the packet

Since all GPRS IP addresses are related to a specific GGSN, anyresponses from the host are always routed to that GGSN

The packet is routed from the host to the GGSN based on thedestination IP address in the packet.


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. The GGSN is the anchor, or owner, of a block of IP addresses and

When the GGSN receives the packet, it consults its routing tableand realizes that the MS which is usin the destination IP addressis currently being served by a particular SGSN

It then envelops the packet in a new packet with the destination,

The SGSN is tracking all mobiles in its coverage area and knowswhere the MS is located i.e. within which cell or rou of cells

It then sends the packet to the mobile via the BSS.

introduction of gprs [compatibility mode]

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