Analysis of quality of service for voice over ip

The cost of providing and running voice services using an IP infrastructure is considerably less than a traditional public exchange system. Therefore, new types of operators selling voice services are emerging that use IP technology, allowing a broader choice of operators for end users. Users however, would like to receive voice quality akin to that provided by the traditional telephony network. Voice services using IP in service today, focus on lower cost and high service quality. The voice quality can be variable when using the IP infrastructure, especially in peak hours. Therefore, to achieve our goal of good quality audio communication, some changes might be needed to the ubiquitous Network. Providing strict quality guarantees has plagued researchers for many years and now industry is facing the same challenges. The degradation of voice quality which can occur when using a multi-user packet switched network is the fundamental problem. Unpredictable short term loads, lack of guarantees on network performance, lack of control over the end systems and stringent requirements on the voice quality make VoIP a challenging application to realize successfully. This thesis proposes and investigates methods to improve quality of voice communication over the Internet Protocol. In the first part of thesis, VoIP system and it?s problems are introduced briefly and compared with VoX technologies. In the second part, historical progress of VoIP and it?s protocols are taken up. SIP and H.323, which are most popular signaling protocols in IP telephony, are also covered on this section. In the third part, Quality of Services concept is explained and various QoS techniques used for bandwidth, delay, jitter and packet loss are given. Performance differences between hardware based QoS and software based QoS are also discussed. In the last part of thesis, a simple Java application developed to determine line quality, whether good or bad, for VoIP. Besides, a test environment is designed. Cisco IAD 2431 8FXS gateways, laptop PCs and analog telephones are used to generate and monitor network traffic including voice, ftp, http and icmp in real time. In this environment, compression, queuing, call admission control and random early drop techniques are used. The implementation is based on a Differentiated Service approach using the DSCP bits of the TOS byte. Keywords: Voice over IP, VoIP, Quality of Service ,QoS