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Mobile Computing - GPRS, Study notes of Mobile Computing

Moradabad Institute of TechnologyMobile Computing

Description about GPRS, three different classes of devices, Classes of GPRS Services, GPRS Network System Architechture, Gateway GPRS Support Node , GPRS Network System Architecture.

Typology: Study notes

2010/2011

Uploaded on 09/04/2011

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GPRS
•General Packet Radio Service (GPRS) is a Mobile Data Service available to users of Global
System for Mobile Communications (GSM) and IS-136 mobile phones. It provides data rates
from 56 up to 114 Kbps.
•GPRS data transfer is typically charged per kilobyte of transferred data, while data
communication via traditional circuit switching is billed per minute of connection time,
independent of whether the user has actually transferred data or has been in an idle state.
GPRS can be used for services such as Wireless Application Protocol (WAP) access, Short
Message Service (SMS), Multimedia Messaging Service (MMS), and for Internet
communication services such as email and World Wide Web access.
•2G cellular systems combined with GPRS is often described as "2.5G", that is, a technology
between the second (2G) and third (3G) generations of mobile telephony. It provides
moderate speed data transfer, by using unused Time division multiple access (TDMA)
channels in, GPRS is integrated into GSM Release 97 and newer releases.
• It was originally standardized by European Telecommunications Standards Institute (ETSI),
but now by the 3rd Generation Partnership Project (3GPP).
•The General Packet Radio Service (GPRS) is a new nonvoice value added service that allows
information to be sent and received across a mobile telephone network. It supplements
today's Circuit Switched Data and Short Message Service. GPRS is NOT related to GPS (the
Global Positioning System), a similar acronym that is often used in mobile contexts.
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GPRS

  • (^) General Packet Radio Service (GPRS) is a Mobile Data Service available to users of Global System for Mobile Communications (GSM) and IS-136 mobile phones. It provides data rates from 56 up to 114 Kbps.
  • (^) GPRS data transfer is typically charged per kilobyte of transferred data, while data communication via traditional circuit switching is billed per minute of connection time, independent of whether the user has actually transferred data or has been in an idle state. GPRS can be used for services such as Wireless Application Protocol (WAP) access, Short Message Service (SMS), Multimedia Messaging Service (MMS), and for Internet communication services such as email and World Wide Web access.
  • (^) 2G cellular systems combined with GPRS is often described as "2.5G", that is, a technology between the second (2G) and third (3G) generations of mobile telephony. It provides moderate speed data transfer, by using unused Time division multiple access (TDMA) channels in, GPRS is integrated into GSM Release 97 and newer releases.
  • (^) It was originally standardized by European Telecommunications Standards Institute (ETSI), but now by the 3rd Generation Partnership Project (3GPP).
  • (^) The General Packet Radio Service (GPRS) is a new nonvoice value added service that allows information to be sent and received across a mobile telephone network. It supplements today's Circuit Switched Data and Short Message Service. GPRS is NOT related to GPS (the Global Positioning System), a similar acronym that is often used in mobile contexts.

GPRS

  • (^) GPRS Handset Classes: There are three different classes of devices.

1. Class A handsets can do both voice and data at the same time

(simultaneously). If you were to receive a voice call will using the

Internet, say, the connection would be placed on busy while you

answer the call, rather than have it disconnected.

2. Class B handsets are voice and packet data capable, but not at the same

time. It can only support either a voice or data service at a time. But

like in Class A above, a voice call would put the data call on hold, and

vice versa.

3. Class C handsets can handle only non-simultaneous data and voice

calls. The user must manually select the service they wish to connect

to. (SMS is also optional for Class C terminals).

GPRS Network System Architechture

  • (^) A GSM network mainly consists of four components.
  • (^) Mobile Station (MS) carried by the subscriber.
  • (^) Base Station Subsystem (BSS) controls radio link with mobile station.
  • (^) Mobile Switching Center (MSC) is the central component of the NSS. Operates

all switching functions for the mobiles within its jurisdiction. Interface

between mobile and other (including fixed) network.

  • (^) Network Databases : Home Location Register and Visitor Location Register

together with MSC provides the call routing and roaming capabilities of GSM.

  • (^) In order to integrate GPRS into the existing GSM network, two major new core

network elements are introduced: the Serving GPRS Support Node (SGSN)

and the Gateway GPRS Support node (GGSN).

  • (^) Serving GPRS Support Node (SGSN): An SGSN is responsible for the delivery of

data packets from and to the mobile stations within its service area. SGSNs

send queries to Home Location Registers (HLRs) to obtain profile data of GPRS

subscribers. SGSNs detect new GPRS mobile stations in a given service area;

and, finally, SGSNs process registration of new mobile subscribers and keep a

record of their location inside a given service area.

GPRS Network System Architechture

  • (^) Gateway GPRS Support Node (GGSN) : GGSNs are used as interfaces

between the GPRS backbone network and the external Public Packet

Data Networks. GGSNs maintain routing information that is necessary

to tunnel the Protocol Data Units (e.g IP) to the SGSNs that service

particular mobile stations. Other functions include network and

subscriber screening and address mapping. One or more GGSNs may

support multiple SGSNs.

  • (^) In addition to the new GPRS components, following existing GSM

network elements must also be enhanced in order to support GPRS.

  • (^) Base Station System (BSS): must be enhanced to recognize and send

user data to the SGSN that is serving the area.

  • (^) Home Location Register (HLR): must be enhanced to register GPRS

user profiles and respond to queries originating from SGSNs regarding

these profiles.

To use GPRS, users specifically need:

  • (^) A mobile phone or terminal that supports GPRS (existing GSM phones do NOT support GPRS)
  • (^) A subscription to a mobile telephone network that supports GPRS;
  • (^) Use of GPRS must be enabled for that user. Automatic access to the GPRS may be allowed by some mobile network operators, others will require a specific opt-in;
  • (^) Knowledge of how to send and/or receive GPRS information using their specific model of mobile phone, including software and hardware configuration (this creates a customer service requirement);
  • (^) A destination to send or receive information through GPRS. Whereas with SMS this was often another mobile phone, in the case of GPRS, it is likely to be an Internet address, since GPRS is designed to make the Internet fully available to mobile users for the first time. From day one, GPRS users can access any web page or other Internet applications- providing an immediate critical mass of uses.

GPRS Services

  • (^) Multimedia Messaging Service (MMS)
  • (^) Push to talk over Cellular PoC / PTT
  • (^) Instant Messaging and Presence -- Wireless Village
  • (^) Internet Applications for Smart Devices through Wireless Application Protocol (WAP)
  • (^) Point-to-point (PTP) service: internetworking with the Internet (IP protocols)
  • (^) Short Message Service (SMS)
  • (^) Future enhancements: flexible to add new functions, such as more capacity, more users, new accesses, new protocols, new radio networks.
  • (^) USB GPRS modem: USB GPRS modems use a terminal-like interface USB 2.0 and later, data formats V.42bis, and RFC 1144 and external antennas. Modems can be add in cards (for laptop) or external USB devices which are similar in shape and size to a computer mouse.
  • (^) GPRS can be used as the bearer of SMS. 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

Features of GPRS

  • (^) Faster data transfer rates GPRS currently supports an average data rate of 115 Kbps, but this speed is only achieved by dedicating all eight time slots to GPRS. Instead, carriers and terminal devices will typically be configured to handle a specific number of time slots for upstream and downstream data. The aggregate cell site bandwidth is shared by voice and data traffic. GPRS operators will vary in how they allocate the bandwidth. Typically, they will configure the networks to give precedence to voice traffic; some may dedicate time slots to data traffic to ensure a minimum level of service during busy voice traffic periods. Unused voice capacity may be dynamically reallocated to data traffic.
  • (^) Always-on connection An “always-on” connection eliminates the lengthy delays required to reconnect to the network to send and receive data. Information can also be pushed to the end user in real time.
  • (^) Robust connectivity GPRS improves data transmission integrity with a number of mechanisms. First, user data is encoded with redundancies that improve its resistance to adverse radio conditions. The amount of coding redundancy can be varied, depending on radio conditions. GPRS has defined four coding schemes CS1 through CS4. Initially, only CS and CS2 will be supported, which allows approximately 9 and 13 Kbps in each time slot.If an error is detected in a frame received in the BSS, the frame may be repeatedly retransmitted until properly received before passing it on to the GPRS core network.

Features of GPRS

  • (^) Broad application support

Like the Internet, GPRS is based on packet-switched data. This means that all

native IP applications, such as email, Web access, instant messaging, and file

transfers can run over GPRS. In addition, its faster data transfer rates enable

GPRS to accommodate higher-bandwidth applications (such as multimedia

Web content) not suited to slower GSM dial-up connections. GPRS is

particularly well suited for applications based on the Wireless Application

Protocol (WAP).

  • (^) Security support

GPRS builds on the proven authentication and security model used by GSM. At

session initiation, a user is authenticated using secret information contained

on a smart card called a Subscriber Identity Module (SIM). Authentication data

is exchanged and validated with records stored in the HLR network node. GPRS

enables additional authentication using protocols such as RADIUS before the

subscriber is allowed access to the Internet or corporate data networks.

GPRS Transmission Plane Protocol Reference Model

GPRS Transmission Plane Protocol Reference Model

  • (^) All data within the GPRS backbone, i.e. between the GSNs (SGSN-GGSN), is

transferred using the GTP (GPRS tunnelling protocol). GTP can use two

different transport protocol, either reliable TCP for X.25 packets or the non-

reliable UDP used for IP packets.

  • (^) To adapt to the different characteristics of the underlying networks, the

Subnetwork Dependent Convergence Protocol (SNDCP) is used between an

SGSN and the MS

  • (^) On top of SNDCP and GTP user packet data is tunneled from the MS to the

GGSN and vice versa.

  • (^) To achieve high reliability of packet transfer between SGSN and MS, a special

LLC is used, which comprises ARQ and FEC mechanisms.

  • (^) A Base Station Subsystem GPRS Protocol (BSSGP) is used to convey routing

and QoS -related information between the BSS and SGSN. BSSGP doesn’t

perform error correction and works on top of Frame relay (FR) network.

Radio Link Control (RLC)

 Segmentation of the LLC-Frames in RLC blocks

Block size dependent on short-term channel conditions

 Backward error correction and data flow control by Automatic

Repeat Request (ARQ) protocol

 repeating not repairable RLC blocks selectively

Medium Access Control ( MAC)

 Channel reservation contains:

  • one/several time slots (Packet Data Channels PDCH) of one

frequency

 one uplink status flag (USF) per Packet Data Channel (PDCH), channel partition of up to 8 ms GPRS: air interface

 (^) Medium Access Control ( MAC)  (^) Reservation in the uplink (MS to BSS):  (^) MS sends reservation request on a Random Access Channel (Slotted ALOHA)  (^) BTS allocates a (split) channel and sends packet assignment  (^) MS sends data depending on the current priority (USF flag)  (^) Reservation in the Downlink (BSS to MS):  (^) BTS displays transmitting request and informs about the reserved channel  (^) MS supervises the reserved channel and receives GPRS: air interface

GPRS Applications

• Chat

• Textual and visual information

• Still & moving images

• Web browsing

• Document sharing/Collaborate working

• Audio

• Email, File Transfer…

GSM Vs. GPRS It is circuit switched. It is packet switched. It is not ‘Always-on’. It is ‘Always-on’. You’re charged for the time the channel is reserved.

- You’re charged for the amount of data that’s being transported, not for the time that the unit is online. The System uses the same TDMA (Time Division Multiple Access) link with one out of seven time slots. The GPRS connection in the t610 can use as many as 4+1 time slots. Circuit switching provides the customer with a dedicated channel all the way to the destination. The customer has exclusive use of the circuit for the duration of the call, With packet switching, the operator assigns one or more dedicated channels specifically for shared use. These channels are up and running 24 hours a day, and when you need to transfer data, you access a channel and transmit your data. The standard data rate of a GSM channel is 22.8 kbps It provides data rates from 56 up to 114 Kbps.