Applications can choose different profiles for throughput. There are 2 distinctions in class, peak and mean. Peak throughput class is used mainly for bursty transmissions with a variable in octets per second describing the throughput required for burst of specified size. Mean is the average data transfer rate over a period of time measured in octets per hour.
Applications can request differing levels of reliability for its data depending on its tolerance to data loss.
Applications can request predictive delay classes which guarantee an average and 95- percentile delay. There are 4 classes, 1 being the fastest.
An application can be assigned a Precedence Class 1, 2 or 3. If an application has a higher precedence (1) than another (3) then its traffic will be given a higher priority.
The Telecommunications Standard Institute has defined 3 new coding schemes for Radio Interface. When the GPRS device talks to the base station they can use 1 of the 4 schemes. The schemes are CS - 1 through CS - 3 where CS - 1 is the same as standard GSM. In simple terms CS - 1 is highly redundant but because of this is slow, 2 and 3 have less redundancy, whilst 4 has the least - removing all forward error control - but is capable of maximum throughput. If radio quality is bad then coding scheme 1 is used, as the quality improves less error control is needed.
Just because GPRS uses many of the components of a standard GSM network it would be foolhardy to assume that the same standards should apply. Things to be taken into account include provider general network architecture, radio interface and throughput. Here are some of the key elements briefly explained.
GPRS devices are not as straightforward as you may think. There are in fact 3 different classes of device.
Class A terminals have 2 transceivers which allow them to send / receive data and voice at the same time. This class of device takes full advantage of GPRS and GSM. You can be taking a call and receiving data all at the same time.
Class B devices can send / receive data or voice but not both at the same time. Generally if you are using GPRS and you receive a voice call you will get an option to answer the call or carry on.
This device only allows one means of connectivity. An example would be a GPRS PCMCIA card in a laptop.
A mobile device is programmed with one or more Access Point Names which are commonly referred to as the APN's. An APN consists of a fully qualified DNS name e.g. globalguideline.com When a GPRS device wants to talk to globalguideline.com, the SGSN does a DNS look up and resolves the name to the correct GGSN. You could have multiple APN's programmed into your phone so you are not limited to a single service or GGSN.
The second means of addressing is dynamic addressing. This is where a mobile device does not have its own IP address stored in the HLR. Instead the IP address is assigned to the GGSN domain. The method is also a type of dynamic IP addressing in which the IP address is assigned by RADIUS servers normally situated inside an IP network outside the mobile network, an example of this being when you dial up to an ISP from your home PC.