Analysis of Quality of Service in Wimax networks

1.1 Quality of Service 
As packets travel within a wireless network such as WiMAX, they experience 
the following problems. 
• 
Delay: Unpredictably longer time for packets to reach the destination 
due to unavailability of network resources. 

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• 
Jitter - Packets from source will reach the destination with different 
delays. This variation in delay is known as jitter and can seriously affect the quality 
of streaming audio and/or video. 
• 
Out-of-order delivery: When a collection of related packets are routed 
through the Internet, different packets may take different routes, each resulting in a 
different delay. The result is that the packets arrive in a different order to the one 
with which they were sent. This problem necessitates special additional protocols 
responsible for rearranging out-of-order packets once they reach their destination. 
• 
Packet loss or Error: Sometimes packets are misdirected, corrupted, or 
completely lost during transit. If the packet was dropped, the receiver has to ask the 
sender to resend it. In case of bit error detected in a packet, the receiver has to detect 
the error and, just as if the packet was dropped, ask the sender to repeat it. 
There is no formal definition of Quality of service. QoS, in the field of 
telephony, was defined in 1994 in the International Telecommunication Union (ITU) 
Recommendation E.800. This definition is very broad, listing 6 primary components: 
Support, Operability, Accessibility, Retainability, Integrity and Security. In 1998, the 
ITU published a document discussing QoS in the field of data networking. The term 
Quality of Service refers to the probability of the telecommunication network meeting 
a given traffic contract. In the field of packet-switched networks and computer 
networking it is used informally to refer to the probability of a packet succeeding in 
passing between two points in the network. Although the name suggests that it is a 
qualitative measure of how reliable and consistent a network is, there are a number of 

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parameters that can be used to measure it quantitatively. These include throughput, 
transmission delay or packet delay, delay jitter, percentage of packets lost etc. 
The use of different kinds of applications in a network, results in 
heterogeneous traffic load. The traffic from different applications may require certain 
type of quality of service, for example,
•
Streaming multimedia may require guaranteed throughput 
•
IP telephony or Voice over IP (VOIP) may require strict limits on jitter 
and delay 
•
Video Teleconferencing (VTC) requires low jitter 
•
Dedicated link emulation requires both guaranteed throughput and 
imposes limits on maximum delay and jitter 
•
A safety-critical application, such as remote surgery may require a 
guaranteed level of availability (this is also called hard QoS).