General Packet Radio Service
Introduction
General Packet Radio Service (GPRS) is a 2.5 generation packet based network technology for GSM networks. GPRS is different from the older Circuit Switched Data (or CSD) connection included in GSM standards. In CSD, a data connection establishes a circuit, and reserves the full bandwidth of that circuit during the lifetime of the connection. GPRS is packet-switched which means that multiple users share the same transmission channel, only transmitting when they have data to send. This means that the total available bandwidth can be immediately dedicated to those users who are actually sending at any given moment, providing higher utilisation where users only send or receive data intermittently. Web browsing, receiving e-mails as they arrive and instant messaging are examples of uses that require intermittent data transfers, which benefit from sharing the available bandwidth.
Usually, GPRS data are billed per kilobytes of information transceived while circuit-switched data connections are billed per second. The latter is to reflect the fact that even during times when no data are being transferred, the bandwidth is unavailable to other potential users.
The multiple access methods used in GSM with GPRS are based on frequency division duplex (FDD) and FDMA. During a session, a user is assigned to one pair of uplink and downlink frequency channels. This is combined with time domain statistical multiplexing, i.e. packet mode communication, which makes it possible for several users to share the same frequency channel. The packets have constant length, corresponding to a GSM time slot. In the downlink, first-come first-served packet scheduling is used. In the uplink, a scheme that is very similar to reservation ALOHA is used. This means that slotted Aloha (S-ALOHA) is used for reservation inquiries during a contention phase, and then the actual data is transferred using first-come first-served scheduling.
GPRS originally supported (in theory) IP, PPP and X.25 connections. The last has been typically used for applications like wireless payment terminals although it has been removed as a requirement from the standard. X.25 can still be supported over PPP, or even over IP, but doing this requires either a router to do encapsulation or intelligence built into the end terminal. In practice, mainly IPv4 is used. PPP is often not supported by the operator, while IPv6 is not yet popular
The GPRS capability classes
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. See List of Class A GPRS Phones.
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.
A true Class A device may be required to transmit on two different frequencies at the same time, and thus will need two radios. To get around this expensive requirement, a GPRS mobile may implement the dual transfer mode (DTM) feature. A DTM-capable mobile may use simultaneous voice and packet data, with the network coordinating to ensure that it is not required to transmit on two different frequencies at the same time. Such mobiles are considered to be pseudo Class A. Some networks are expected to support DTM in 2007.
GPRS multislot classes
GPRS speed is a direct function of the number of TDMA time slots assigned, which is the lesser of (a) what the particular cell supports and (b) the maximum capability of the mobile device expressed as a GPRS Multislot Class.
| Multislot Class | Downlink Slots | Uplink Slots | Active Slots |
|---|---|---|---|
| 1 | 1 | 1 | 2 |
| 2 | 2 | 1 | 3 |
| 3 | 2 | 2 | 3 |
| 4 | 3 | 1 | 4 |
| 5 | 2 | 2 | 4 |
| 6 | 3 | 2 | 4 |
| 7 | 3 | 3 | 4 |
| 8 | 4 | 1 | 5 |
| 9 | 3 | 2 | 5 |
| 10 | 4 | 2 | 5 |
| 11 | 4 | 3 | 5 |
| 12 | 4 | 4 | 5 |
| 32 | 5 | 3 | 6 |
The most common GPRS multislot classes are:
Class 2 --Minimal GPRS implementation
Class 4 --Modest GPRS implementation, 50% faster download than Class 2
Class 6 --Modest implementation, but with better uploading than Class 4
Class 8 --Better implementation, 33% faster download than Classes 4 & 6
Class 10 --Better implementation, and with better uploading than Class 8, seen in better cell phones and PC Cards
Class 12 --Best implementation, with maximum upload performance, typically seen only in high-end PC Cards
Class 2 --Minimal GPRS implementation
Class 4 --Modest GPRS implementation, 50% faster download than Class 2
Class 6 --Modest implementation, but with better uploading than Class 4
Class 8 --Better implementation, 33% faster download than Classes 4 & 6
Class 10 --Better implementation, and with better uploading than Class 8, seen in better cell phones and PC Cards
Class 12 --Best implementation, with maximum upload performance, typically seen only in high-end PC Cards
Data Speed
GPRS data speeds are expected to reach theoretical data speeds of up to 171.2 Kbps. However, this is based on optimal conditions in terms of available cell/sector capacity in terms of available time slots, maximum coding scheme (CS-4) as well as moible phone availability to support the maximum number of time slots - eight. More practical data rates are currently in the order of 40-60 Kbps.
3G technologies such as W-CDMA will theoreticaly provide up to 2 Mbps in a fixed location. There will, however, be some significant limitations to this theoretical capacity. While 3G (and beyond) is expected to usher in the advent of high-bandwidth, multi-media services, the real impetus for2.5G and packet based mobile data lies elsewhere.
Impetus for GPRS
The major impetus for GPRS and other packet based mobile data technologies is the "always-on" capability. Being packet based, GPRS allows for the use of infrastructure and facilities only when a transaction is required, rather than maintaining facilities in a session-like manner. This provides tremendous infrastructure efficiency and service delivery improvements.
Using GPRS as a bearer for WAP, for instance, will allow for the use of WAP on a per-transaction rather than a per-minute-of-use basis. More importantly perhaps is the ability for GPRS to allow for autonomous service realization through the always-on capability. For example, a GPRS customer could receive content or services without actually manually invoking a service or transaction. This has significant implications for mobile commerce and location based services.GPRS Architecture and Issues
GPRS architecture consists of Gateway GPRS Support Node (GGSN) and a Serving GPRS Support Node (SGSN). The GGSN acts as the gateway to other packet data networks such as the Internet. The SGSN is the serving node that enables virtual connections to the GPRS enabled mobile device and delivery of data.
The blessing and curse of the SGSN is that it supports an attach state when a user is engaged in GPRS data usage and a detach state when idle. The idle state creates a particular challenge for attempting to position the unit for location based services. In addition, GPRS presents a challenge in terms of the ability to offer prepaid mobile data services, which may be overcome by the introduction of CAMEL and perhaps the use of Parlay.
The evolution from GPRS to W-CDMA entails upgrade of the Radio Access Network (RAN) to include two new network elements. The Node B replaces the BTS and the Radio Network Controller (RNC) replaces the BSC in the RAN. However, mobile network operators will maintain their GPRS assets for that service and thus maintain the existing network elements along with the new ones for 3G. W-CDMA continues to use the same Core Network (CN) elements as GPRS.
Deployment and Operational Issues
Beyond the scope of this white paper, there are several significant issues associated with deployment and operation of GPRS systems. Those issues include:
GPRS data speeds are expected to reach theoretical data speeds of up to 171.2 Kbps. However, this is based on optimal conditions in terms of available cell/sector capacity in terms of available time slots, maximum coding scheme (CS-4) as well as moible phone availability to support the maximum number of time slots - eight. More practical data rates are currently in the order of 40-60 Kbps.
3G technologies such as W-CDMA will theoreticaly provide up to 2 Mbps in a fixed location. There will, however, be some significant limitations to this theoretical capacity. While 3G (and beyond) is expected to usher in the advent of high-bandwidth, multi-media services, the real impetus for2.5G and packet based mobile data lies elsewhere.
Impetus for GPRS
The major impetus for GPRS and other packet based mobile data technologies is the "always-on" capability. Being packet based, GPRS allows for the use of infrastructure and facilities only when a transaction is required, rather than maintaining facilities in a session-like manner. This provides tremendous infrastructure efficiency and service delivery improvements.
Using GPRS as a bearer for WAP, for instance, will allow for the use of WAP on a per-transaction rather than a per-minute-of-use basis. More importantly perhaps is the ability for GPRS to allow for autonomous service realization through the always-on capability. For example, a GPRS customer could receive content or services without actually manually invoking a service or transaction. This has significant implications for mobile commerce and location based services.GPRS Architecture and Issues
GPRS architecture consists of Gateway GPRS Support Node (GGSN) and a Serving GPRS Support Node (SGSN). The GGSN acts as the gateway to other packet data networks such as the Internet. The SGSN is the serving node that enables virtual connections to the GPRS enabled mobile device and delivery of data.
The blessing and curse of the SGSN is that it supports an attach state when a user is engaged in GPRS data usage and a detach state when idle. The idle state creates a particular challenge for attempting to position the unit for location based services. In addition, GPRS presents a challenge in terms of the ability to offer prepaid mobile data services, which may be overcome by the introduction of CAMEL and perhaps the use of Parlay.
The evolution from GPRS to W-CDMA entails upgrade of the Radio Access Network (RAN) to include two new network elements. The Node B replaces the BTS and the Radio Network Controller (RNC) replaces the BSC in the RAN. However, mobile network operators will maintain their GPRS assets for that service and thus maintain the existing network elements along with the new ones for 3G. W-CDMA continues to use the same Core Network (CN) elements as GPRS.
Deployment and Operational Issues
Beyond the scope of this white paper, there are several significant issues associated with deployment and operation of GPRS systems. Those issues include:
- Capacity and network optimization
- Handset availability and performance
- Quality of service
- Charging for services
GPRS services and hardwar
GPRS upgrades GSM data services providing:
- Push To Talk over Cellular PoC / PTT - Push to talk
- Instant Messaging and Presence Wireless_Village
- Internet Applications for Smart Devices through WAP
- Point-to-point (PTP) service: internetworking with the Internet (IP protocols).
- Short Message Service (SMS): bearer for SMS.
- Future enhancements: flexible to add new functions, such as more capacity, more users, new accesses, new protocols, new radio networks
Gprs core Network--> click here
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