How GPRS Works

Hi All,

   Lets have some details regarding GPRS Working, As we all know, It’s a Packet Switched Network, 

          

          In a GPRS Network, a user station doesn't occupy a dedicated path during an Internet connection. However, each end user station (e.g. mobile phone) is allocated several time slots out of 8 GSM/TDMA available time-slots for GPRS service. 

          
          Each time slot has a maximum capacity of 14.4 kbps, depending on how many time slots are allocated for the downlink (from a base station to a user station) and the uplink (from a user station to a base station), 

          
          GPRS devices are divided into multi-slot classes. A multi-slot class is often represented by the number of downlink and uplink slots. For example, Class 10 is also known as Class 4+2. While active slots indicate the maximum number of slots that can be allocated for both downlink and uplink in a specific class.

Class Types :-

• 2+1 (two slots for download + 1 for upload)
• 3+1 (three slots for download + 1 for upload)
• 4+1 (four slots for download + 1 for upload)

          GPRS is a mobile data upgrade to a GSM mobile phone network. This provides users with packet data services (similar to the Internet) using the GSM digital radio network. Each voice circuit in GSM transmits the speech on a secure 14kbps digital radio link between the mobile phone and a nearby GSM transceiver station.

          The GPRS service joins together multiple speech channels to provide higher bandwidth data connections for GPRS data users. The radio bandwidth remains the same, it is just shared between the voice users and the data users. The network operator has the choice of prioritizing one or the other.

           
          GPRS users will also benefit from being able to use GPRS while traveling as the GSM system should transparently hand over the GPRS connection from one base station to another.

GPRS Roaming - There are two type of GPRS Roaming

Home Network Roaming - Here all data is transmitted from wherever you connect to a GPRS network to your home GPRS network where it is connected to the Internet or your company LAN as if you were indeed in your home country.

Local Network Roaming - Data is just connected to a local Internet connection point and will be subject to local conditions for security and performance.

Radio Interface

           
          Each GSM radio transceiver uses Time Division Multiplexing to deliver eight voice circuits on one radio channel. Each radio site may have one or more transceivers to provide sufficient channels to end users (maximum numbers are limited by many factors including - operators radio license, interference with other nearby GSM cells, cost of equipment, capacity of radio site infrastructure, etc.)

          Each 14kbps channel may be shared by multiple 'connected' GPRS users (many users will be connected to the network but transmitting very little data). As a user's data requirements grow, they will use more of the available capacity within that timeslot, and then more available timeslots up to the maximum available or the maximum supported by their device.

In general the higher the data rate, the more power the mobile device will use and the shorter the battery life and the higher the transmitted RF power.

GPRS Tunneling Protocols will be updated soon….

Comments and Appreciations are most welcome.

ChEeEeEeErRrRrRs!!!

Telecom Tigers Team

telecomtigers@gmail.com

http://homepageforu.webs.com/

GPRS Call Flow

            GPRS (General Packet Radio Service) is a packet based communication service for mobile devices that allows data to be sent and received across a mobile telephone network. It's a step towards 3G and is often referred to as 2.5G.
            It’s an upgrade to the existing network that sits along side the GSM network. Many of the devices such as the BTS and BSC are still used. Often devices need to be upgraded be it software, hardware or both. When deploying GPRS many of the software changes can be made remotely.
           There are however 2 New Functional Elements which play a major role in how GPRS works - SGSN & GGSN. In simple terms there are in practice two different networks working in parallel, GSM and GPRS.
           In any GSM network there will be several BSC’s. When implementing GPRS a software and hardware upgrade of this unit is required. The hardware upgrade consists of adding a PCU (Packet Control Unit). This extra piece of hardware differentiates data destined for the standard GSM network or Circuit Switched Data and data destined for the GPRS network or Packet Switched Data.
PCU can be a separate entity.

SGSN (Serving GPRS Support Node) - It takes care of some important tasks, including Routing, Handover and IP address assignment. Its a logical connection to the GPRS device. One job of the SGSN is to make sure the connection is not interrupted as you make your journey passing from cell to cell. It works out which BSC to “route” your connection through. If the user moves into a segment of the network that is managed by a different SGSN it will perform a handoff to the new SGSN, this is done extremely quickly and generally the user will not notice this has happened. Any packets that are lost during this process are retransmitted. The SGSN converts mobile data into IP and is connected to the GGSN via a tunneling protocol.

GGSN (Gateway GPRS support node) - It is the “last port of call” in the GPRS network before a connection between an ISP (Internet Service Provider) or corporate network’s router occurs. The GGSN is basically a gateway, router and firewall. It also confirms user details with RADIUS servers for security, which are usually situated in the IP network and outside of the GPRS network.
            The connection between the two GPRS Support Nodes is made with a protocol called GPRS Tunneling Protocol (GTP). GTP sits on top of TCP/IP and is also responsible for the collection of mediation and billing information. GPRS is billed on per megabyte basis.

GPRS Call Scenario :-

• A subscriber accesses the Internet with GPRS mobile phone to set the APN (Access Point Names) & gateway IP address defined on subscription. In fact, APN is a logical name indicating the external data network in GGSN. A subscriber can select different GGSNs via different APNs. Currently, however, only one APN can be activated at a time. The purpose of selecting different APNs is to access the external network via different GGSNs, because without GGSN, a subscriber cannot access the PDN (Public Data Network). An APN consists of a fully qualified DNS (Domain Name Server) name e.g. airtellive.com.cn., which should be parsed by DNS to get the real IP address of GGSN.
• The call reaches the SGSN of the GPRS network. The SGSN triggers the service in the corresponding SCP (Service Control Point) according to subscriber's authentication information on the HLR interconnected to the corresponding home SCP for processing.
• The DNS parses the APN and get the IP address of the GGSN.
• The call is routed to the GGSN according to the IP address.
• The GGSN assigns the IP address to the subscriber.
• After SCP verifies the subscriber, the subscriber begins to transmit data and log in to the external web sites via the gateway whose IP address is set in the mobile phone.
• The subscriber may select the service from the portal web site to connect the SP/CP web site that provides the service, or enter the IP address of the SP/CP in the mobile phone to access the SP/CP web site.

More Information from Readers are Expected !!!


Thanks
telecomtigers@gmail.com
http://homepageforu.webs.com/

What is GPRS

GPRS (General Packet Radio Service)

It is a non-voice service added to existing TDMA networks, It is an enhancement to GSM or TDMA (IS-95) network. It uses existing cellular network infrastructure with software upgrade at base stations and the addition of a GPRS Gateway that connects the GPRS network to the Internet.
TDMA is the underlying transport mechanism used by GSM networks.
GPRS provides the transmission of IP packets over existing cellular networks.

GPRS Architecture -

Components :-

1. SGSN (Serving GPRS Support Node) - It monitors the state of the mobile station and tracks its movements within a given geographical area. It is also responsible for establishing and managing the data connections between the mobile user and the destination network.
2. GGSN (Gateway GPRS Support node) - It provides the point of attachment between the GPRS domain and external data networks such as the internet and Corporate Intranets. Each external network is given a unique Access Point Name (APN) which is used by the mobile user to establish the connection to the required destination network.
3. WAP Servers - Its used for General Information Services like Train Timetables, etc.
4. RADIUS Server - Remote Access Dial-in User Server. 

GPRS Mobile devices

The key use for GPRS is to send and receive data to a computer application such as Email, web browsing or even telemetry (telemetry refers to devices not being controlled by humans such as cash point machines or traffic monitoring cameras etc.). To use GPRS the service is 'dialed' in a similar manner to a standard data call (though there is no phone no.) at which point the user is 'attached' and an IP address is allocated. From then on data can flow to and from the Internet until either the network unattaches you (maybe because of a time-out, fault or congestion) or you manually unattach.

Some of the key issues are:

• Using GPRS will not stop you making or receiving voice calls.Current phones will usually suspend the data session while a voice call takes place.
• Battery life will be reduced when using GPRS.
• Do not keep it near your ear for long periods while data transfers are taking place.

As a business GPRS user you will have a choice of methods to connect to the GPRS network - by far the most common method will be via the Internet. For larger users you may connect your company LAN to the GPRS networks using leased lines or Frame Relay virtual circuits.

Thanks
telecomtigers@gmail.com
http://homepageforu.webs.com/