Gprs

CONTENTS

• INTRODUCTION

• ARCHITECTURE.

• GPRS OPERATIONS.

• USERS BENEFITS

• APPLICATIONS

• ADVANTAGES

• CONCLUSION

INTRODUCTION
What is GPRS?

GSM was the most successful second generation cellular technology, but the need for higher data rates spawned new developments to enable data to be transferred at much higher rates. The first system to make an impact on the market was GPRS. The letters GPRS stand for General Packet Radio System, GPRS technology enabled much higher data rates to be conveyed over a cellular network when compared to GSM that was voice centric.
General Packet Radio Service • General: not restricted to GSM use (DECT?, 3rd generation systems?) • Packet Radio: enables packet mode communication over air • Service, not System: existing BSS (partially also NSS) infrastructure is used
GPRS became the first stepping-stone on the path between the second-generation GSM cellular technology and the 3G W-CDMA / UMTS system. With GPRS technology offering data services with data rates up to a maximum of 172 kbps, facilities such as web browsing and other services requiring data transfer became possible. Although some data could be transferred using GSM, the rate was too slow for real data applications.
General Packet Radio Service is a radio technology for GSM networks that adds packet-switching protocols, shorter set-up time for ISP connections; it also offers the possibility to charge by amount of data sent rather than connect time.

Key GPRS parameters

The key parameters for the GPRS, General Packet Radio System, are tabulated below:
Parameter Specification
Channel Bandwidth 200 kHz
Modulation type GMSK
Data handling Packet data
Max data rate 172 kbps

GPRS NETWORK ARCHITECTURE
With GPRS providing additional connectivity in terms of packet data, there are naturally a number of upgrades needed to the network architecture required. A number of new elements are needed for the network, but these can operate alongside the existing elements meaning that the GPRS capability is an upgrade to the network and not a completely new network structure.
The main new network architecture entities that are needed are:
SGSN: GPRS Support Node - this forms a gateway to the services within the network.
GGSN: Gateway GPRS Support Node which forms the gateway to the outside world.
PCU: Packet Control Unit which differentiates whether data is to be routed to the packet switched or circuit switched networks.
A simplified view of the GPRS network architecture can be seen in the diagram below. From this it can be seen that it is very similar to the more basic GSM network architecture, but with additional elements.
[pic]

SGSN

The SGSN or Serving GPRS Support Node element of the GPRS network provides a number of takes focussed on the IP elements of the overall system.There is a location register within the SGSN and this stores location information (e.g., current cell, current VLR). It also stores the user profiles (e.g., IMSI, packet addresses used) for all the GPRS users registered with the particular SGSN.

GGSN

The GGSN, Gateway GPRS Support Node is one of the most important entities within the GPRS network architecture.
The GGSN organizes the interworking between the GPRS network and external packet switched networks to which the mobiles may be connected. These may include both Internet and X.25 networks.
The GGSN can be considered to be a combination of a gateway, router and firewall as it hides the internal network to the outside. In operation, when the GGSN receives data addressed to a specific user, it checks if the user is active, then forwarding the data. In the opposite direction, packet data from the mobile is routed to the right destination network by the GGSN.

PCU

The PCU or Packet Control Unit is a hardware router that is added to the BSC. It differentiates data destined for the standard GSM network (circuit switched data) and data destined for the GPRS network (Packet Switched Data). The PCU itself may be a separate physical entity, or more often these days it is incorporated into the base station controller, BSC, thereby saving additional hardware costs.

GPRS OPERATIONS

When looking at the way in which GPRS operates, it can be seen that there are three basic modes in which it operates. These are: initialization / idle, standby, and ready.

Initialization/Idle

When the mobile is turned on it must register with the network and update the location register. This is very similar to that performed with a GSM mobile, but it is referred to as a location update. It first locates a suitable cell and transmits a radio burst on the RACH using a shortened burst because it does not know what timing advance is required. The data contained within this burst temporarily identifies the mobile, and indicates that the reason for the update is to perform a location update/

When the mobile performs its location update the network also performs an authentication to ensure that it is allowed to access the network. As for GSM it accesses the HLR and VLR as necessary for the location update and the AuC for authentication. It is at registration that the network detects that the mobile has a GPRS capability. The SGSN also maintains a record of the location of the mobile so that data can be sent there is required.

Standby

The mobile then enters a standby mode, periodically updating its position as required. It monitors the MNC of the base station to ensure that it has not changed base stations and also looks for stronger base station control channels.

The mobile will also monitor the PPCH in case of an incoming alert indicating that data is ready to be sent. As for GSM, most base stations set up a schedule for paging alerts based on the last figures of the mobile number. In this way it does not have to monitor all the available alert slots and can instead only monitor a reduced number where it knows alerts can be sent for it. In this way the receiver can be turned off for longer and battery life can be extended.

Ready

In the ready mode the mobile is attached to the system and a virtual connection is made with the SGSN and GGSN. By making this connection the network knows where to route the packets when they are sent and received. In addition to this the mobile is likely to use the PTCCH to ensure that its timing is correctly set so that it is ready for a data transfer should one be needed.

With the mobile attached to the network, it is prepared for a call or data transfer. To transmit data the mobile attempts a Packet Channel Request using the PRACH uplink channel. As this may be busy the mobile monitors the PCCCH which contains a status bit indicating the status of the base station receiver, whether it is busy or idle and capable of receiving data. When the mobile sees this status bit indicates the receiver is idle, it sends its packet channel request message. If accepted the base station will respond by sending an assignment message on the PAGCH on the downlink. This will indicate which channel the mobile is to use for its packet data transfer as well as other details required for the data transfer.

This only sets up the packet data transfers for the uplink. If data needs to be transferred in the downlink direction then a separate assignment is performed for the downlink channel.

When data is transferred this is controlled by the action of the MAC layer. In most instances it will operate in an acknowledge mode whereby the base station acknowledges each block of data. The acknowledgement may be contained within the data packets being sent in the downlink, or the base station may send data packets down purely to acknowledge the data.

When disconnecting the mobile will send a packet temporary block flow message, and this is acknowledged. Once this has taken place the USF assigned to the mobile becomes redundant and can be assigned to another mobile wanting access. With this the mobile effectively becomes disconnected and although still attached to the network no more data transfer takes place unless it is re-initiated. Separate messages are needed to detach the mobile from the network.

USERS BENEFITS
GPRS technology brings a number of benefits for users and network operators alike. It was widely deployed to provide a realistic data capability via cellular telecommunications technology.

GPRS technology offered some significant benefits:

Speed: One of the headline benefits of GPRS technology is that it offers a much higher data rate than was possible with GSM. Rates up to 172 kbps are possible, although the maximum data rates realistically achievable under most conditions will be in the range 15 - 40 kbps.

Packet switched operation: Unlike GSM which was used circuit switched techniques, GPRS technology uses packet switching in line with the Internet. This makes far more efficient use of the available capacity, and it allows greater commonality with Internet techniques.

Always on connectivity: A further advantage of GPRS is that it offers an "Always On" capability. When using circuit switched techniques, charges are based on the time a circuit is used, i.e. how long the call is. For packet switched technology charges are for the amount of data carried as this is what uses the services provider's capacity. Accordingly, always on connectivity is possible.

GPRS roaming: GPRS roaming is a basic requirement for making future global mobile Internet services possible for GPRS subscribers in other operators' GPRS networks.

Motorola's GPRS solution introduces two new network nodes into the GSM PLMN (Public Land Mobile Network) - the SGSN and the GGSN.

A number of new interfaces are added to connect the SGSN and GGSN to the appropriate GSM and non-GSM elements required to provide global packet data service.

APPLICATION
Chat: Because of its synergy with the Internet, GPRS would allow mobile users to participate fully in existing Internet chat groups rather than needing to set up their own groups that are dedicated to mobile users. Since the number of participants is an important factor determining the value of participation in the newsgroup, the use of GPRS here would be advantageous. As such, given the installed base of SMS capable devices, we would expect SMS to remain the primary bearer for chat applications in the foreseeable future, although experimentation with using GPRS is likely to commence sooner rather than later.

Textural and Visual Information: A wide range of content can be delivered to mobile phone users ranging from share prices, sports scores, weather, flight information, news headlines, prayer reminders, lottery results, jokes, horoscopes, traffic, location sensitive services and so on. This information need not necessarily be textual- it may be maps or graphs or other types of visual information.

The length of a short message of 160 characters suffices for delivering information

Still Images: Still images such as photographs, pictures, postcards, greeting cards and presentations, static web pages can be sent and received over the mobile network as they are across fixed telephone networks. It will be possible with GPRS to post images from a digital camera connected to a GPRS radio device directly to an Internet site.

Corporate Email: Since GPRS capable devices will be more widespread in corporations than amongst the general mobile phone user community, there are likely to be more corporate email applications using GPRS than Internet email ones whose target market is more general.

ADVANTAGES
GPRS-enabled mobile phones also double up as portable Internet connections for laptops. In some cases, where Internet access is not readily available but a mobile network is, GPRS can be a lifesaver. Most phones can be used as a modem once connected to a laptop.
The advantage of GPRS, in today’s technological environment, is that it is a great backup option. The portability factor has diminished somewhat, with the advent of much faster data cards, which plug directly into the laptop. GPRS brought mobile phone users out from the world of WAP, and into a world where Internet was finally available on mobiles. This in itself was a monumental feat, and hence GPRS took off with quite a bang. With GPRS, large amounts of data can be transferred to and from the mobile device over the Internet.

CONCLUSION
The GPRS network can be viewed as an evolution of the GSM network carrying both circuit switched and packet data. The GPRS network was also used as the basis for the 3G UMTS network. In this way network operators could evolve their networks through GPRS and possibly EDGE to the full 3G networks without having to replace and install more new equipment than was absolutely necessary. It was widely used, before mobile phones started becoming Wi-Fi enabled. It is very much in the backseat as of now, although it presents a viable alternative in emergencies, when other means of connecting to the Internet are not available.