and in the area of web hosting, technologies such as load balancing provides the means to 

handle huge number of simultaneous requests to services. Although ever increasing 

bandwidth and over provisioning can help to improve conditions, there are a number of 

reasons why the introduction of QoS is still necessary. 

Networks, systems and applications are susceptible to congestion and overload that can 

affect data throughput because application traffic is unpredictable by nature. Since these 

applications often share the same resources at the same time, congestion is often the 

result. Web sites can be hit due to a massive increase in traffic or what is known in the 

Internet world as   the Slastdot Effect  [8]. This often results in what seemed like over 

provisioned servers and networks to quickly appear insufficient due to sheer volume of 

attempts to reach a site simultaneously. There are simply too many users now on the web 

to deliver a first class service all the time based on best effort. 

Different applications have different requirements for throughput, reliability, delay and 

jitter. Some service are more elastic that others. Although users are normally prepared to 

put up with delay with elastic applications

1

 because it is expected to be delivered later in 

the day and picked up some other time, one may send an urgent email which can be 

treated as a real time or inelastic application [9]

.

 So it would be more efficient if one 

could segment traffic based on its requirements for delay, jitter etc. Even on relatively 

unloaded IP networks, delivery delays can vary enough to adversely applications that 

have real time constraints [3]. 

Certain users are willing to pay for a guaranteed service, while others are willing to 

suffice with a  best effort .  Since QoS provides value in the service, it implies the need 

for 

accounting and billing.  

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