Note :- This is a technical article. I have tried to make it look as simple as possible.
Web applications are of different types :-
a) I might be seeing and listening to a music video in YouTube on a mobile phone.
b) I might try to be accessing my email on my mobile phone.
c) I might try to talk using an IP phone.
d) I might try to download a video clip/application.
As we have different types of applications which I have labeled as a), b) c) and d) we also require a quality of service for each of the above web based application.
"a)" is an application whose nature may be defined as "streaming multimedia may require guaranteed throughput"
"b)" (and sometimes "d)" ) are examples of elastic web applications whose nature is very flexible. (elastic applications can take advantage of however much or little bandwidth is available.)
"c)" requires strict limits on jitter and delay.
Now given the different nature of the above web applications, How can GPRS (as a service) address these demands.
The answer, my friend, is QoS aka Quality of Service.
The QoS is a collection of different parameters which have been defined, redefined, abused from release to release. Let us have a quick look on the different parameters of QoS from a GPRS point of view.
Important note of the author
These are just major Release 99 parameters defined in the 3GPP specifications)
a)Precedence class :- This indicates the precedence/priority of an application. Once gain we have precedence 1 , precedence 2 and precedence level 3 classes.
b)Delay class :- The delay parameter is defined as the end to end transfer time between two MSs or between a MS and Gi interface (see Figure 3-1) to an external IP network
c)Reliability Class :- This talks about the reliability of a data transfer of an application.What are the dangers for a packet in a packet network ? It might get corrupted, it can get lost , it can be duplicated or it can be out of sequence. Reliability classes can be 1,2 or 3. 3 provides error correction and is not error sensitive at the receiver end. 1 is error sensitive and provides ZERO error correction.
d)mean throughput :- This is perhaps the most important and visible feature of the QoS. It is the mean octet per sec measure at the Gi interface!!!!
e)peak throughput class :- This is the peak octet rate per sec.
A realistic bit rate is 30–80 kbps, because it is possible to use max 4 time slots for downlink.
A change to the radio part of GPRS called EDGE(sometimes called EGPRS or Enhanced GPRS however it actually stands for Enhanced Data rates for GSM Evolution) allows higher bit rates of between 160 and 236.8 kbit/s.
