LTE LTE LTE! It’s all we’ve been talking about. But as mentioned in previous articles, it is important to appreciate our past, GSM specifically. One integral part of the GSM network is the GPRS (General Packet Radio Service), a non-voice service added to existing TDMA networks, one of the 2.5G technology upgrades. TDMA is the underlying transport mechanism used by GSM networks. GPRS provides the transmission of IP packets over existing cellular networks.
How does GPRS work?
According to www.geekzone.com, GPRS is a network overlay of the existing cellular network and it uses the nature of IP transmissions to its advantage. Because IP traffic is made of “packets”, the network does not need to have continuous data transmission. Therefore, IP traffic can easily share channels. “A user may be receiving or transmitting data while another one is reading information. The second user does not need to use the channel during this time, and it makes packet networks more efficient than circuit-switched networks (2G), where the channel would be in use, regardless of the user transmitting or not.”
Each and every channel is divided into eight time slots, with a maximum data transmission of 13.4Kbps. One time slot is used for control. The other two time slots are reserved for voice traffic. Asymmetric traffic (more download than uploads) dictates the distribution of the remaining time slots:
| Type | Meaning |
| 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 devices are classified by their ability to handle GSM voice calls and GPRS connections:
| Class | Meaning |
| A | devices are capable of simultaneous voice and data transmission |
| B | devices support one type at a time, and switch automatically between data and voice |
| C | devices support one type at a time, and require user intervention to switch between data and voice |
How to use GPRS
Users can connect to GPRS and enable network in three different ways:
| Using a mobile with a microbrowser to access WAP pages | A user can connect to the GPRS and browse WAP pages from a GPRS enabled mobile. Of course the impact of reduced content on WML format and using the little phone keypad to type in URLs is tiresome. Examples are mobile phones such as Ericsson T39m and T68i. |
| Using a handheld with built in GSM/GPRS capabilities | Using handhelds with GPRS capabilities a user can connect to the GPRS network. All Internet services will be available, providing the needed ports are not blocked. This includes web, e-mail, newsgroups, VPN, ftp, etc. The connection between the terminal and the GPRS modem can be via infrared, serial cable or bluetooth. Examples are Treo, XDA Pocket PC Phone Edition, and Smartphones. |
| Using a mobile as a GPRS modem | A user can connect a notebook, desktop or handheld to connect to a GPRS enabled mobile, and then connect to the Internet. All Internet services will be available, providing the needed ports are not blocked. This includes web, e-mail, newsgroups, VPN, ftp, etc. The connection between the terminal and the GPRS modem can be via infrared, serial cable or bluetooth. Examples are using a H3970 to link via Bluetooth to a T39m and from there to the Internet. |
| Using a PCMCIA card as a GPRS modem | A PCMCIA card can be used as a GPRS enabled modem, and once inserted a dial up connection can be created. From there the user can connect to the Internet. All Internet services will be available, providing the needed ports are not blocked. This includes web, e-mail, newsgroups, VPN, ftp, etc. |
What can I do with GPRS?
GPRS allows you to do basically anything that is allowed on the Internet, according to www.geekzone.com. This includes Web browsing, email, VPN connections, Instant Messenger (AOL, ICQ, MSN Messenger) and more. What performance can you expect? It depends on signal strength and the number of users in the channel. www.geekzone.com did some testing on this theory. “Don’t expect blazing performance. In my test, with my local GSM provider, I’ve got results sometimes lower than dial up. But these are non-scientific results.” [1]
GSM Vs. GPRS
So, how do GSM and GPRS work against one another? In a circuit switched call, a user is dedicated resources (frequency and time-slot combination) during the call setup, and has exclusive use of those resources for the duration of the call.
This design is perfect for voice calls as the traffic is generally continuous and symmetrical (an equal amount of data is flowing in the uplink and the downlink). However when it comes to transferring packet data, this design is an inefficient way to do so because it is generally asymmetrical.
GPRS extends GSM by allowing multiple users to share a single resource. This allows the precious air interface resources to be used more efficiently. GPRS allows users to take turns sending 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. [2]
[1] What is GPRS? http://www.geekzone.co.nz/content.asp?contentid=207
[2] General Packet Radio Service, LteWorld, http://lteworld.org/wiki/general-packet-radio-service-gprs
