International Journal on Recent and Innovation Trends in Computing and Communication ISSN: 2321-8169 Volume: 3 Issue: 5 3256 – 3260 _______________________________________________________________________________________________ 3256 IJRITCC | May 2015, Available @ http://www.ijritcc.org _______________________________________________________________________________________ A Survey on Enhancing the QoS through voice Quality for Voice over Wireless LANs (VoWLAN) Girish Tiwari 1 Deptt. Of Electronics and Communication Engg. Ujjain Engineering College Ujjain, (M.P.) India e-mail: tiwari_girish@yahoo.com Manish Kumar Giri 2 Deptt. Of Electronics and Communication Engg. Ujjain Engineering College Ujjain, (M.P.) India e-mail: manishgiri88@gmail.com Abstract— Voice over Internet Protocol (VoIP) is one of the important technologies that allow voice transmission over the IP network. Various voice codec are available for VoIP as this is a rapidly changing technology. It can be an effective renewal for the traditional telephone systems (PSTN) because of extreme utilization of its sources as well as to provide very low cost. Apart from, Wireless Local Area Network (WLAN) has become apparent as a durable networking technology. Hence, the combination of these two popular technologies is growing so fast all over the world. Voice over WLAN will be a tool to provide low-cost and reliable voice services on wireless media. However just like other wireless applications, VoWLAN has also faced few challenges that need to be considered. Quality of Service (QoS) is one of the primary requirements in different kind of wireless applications. In this survey some of the important QoS requirement (latency, delay, jitter etc) have been analyzed, and it also has the introspection of the E- model and MOS (Mean Opinion Score) value for voice quality while using of different ITU-T codec. Therefore it makes Voice over WLAN a challenging research topic. In this study we will address all VoWLAN issues. Keywords- Wireless LAN,Codec, Quality of Service, Voice over WLAN. __________________________________________________*****_________________________________________________ I. INTRODUCTION A. Voice over IP (VoIP) The major classification of VoWLAN is IEEE 802.11 WLAN (wireless local area network) and VoIP (Voice over IP). Combining both of these technologies into a new variety of technology Voice over WLAN (VoWLAN) [1] has been an infrastructure for the provision of low-cost wireless voice services. With the advent of wireless networks in the communication technology field, there are many applications which are benefiting from out of exploiting robust features of wireless networks. Among various applications of wireless network, Voice over IP (VoIP) is one of such applications. The main reason behind this fact is its ability of accepting the challenges of real time delivery of voice packets across networks while utilizing the present internet protocol (IP). Since the past two decades, IP telephony service has reached to new high, one can anticipate it as a viable alternative to the conventional voice service being exercised over public switched telephone networks (PSTN) due to its cost effectiveness factor. B. VoIP components VoIP consists of three components - CODEC (Coder/Decoder), packetizer and playout buffer [2]. At the transmitter side, an appropriate sample of analog voice signals are converted into digital signals, compressed and then encoded into a prearranged format using voice codec. There are voice codecs according to the standards of International Telecommunication Union-Telecommunication (ITU-T) such as G.711 (data rate 64 kbps), G.729 (data rate 8 kbps), etc. Next, process performed is packetization. In which voice is encoded into equal size of packets. Moreover, in each packet, some protocol headers from unfamiliar additional layers are fastened to the encoded voice [3]. These protocol headers are Data link layer header, IP (Internet Protocol), RTP (Real-time Transport Protocol), and UDP (User Datagram Protocol). RTP and RTCP (Real-Time Control Protocol) also support various multimedia applications. Since TCP transport protocol is generally used in the internet, UDP protocol is mainly preferred in VoIP and other delay sensitive real-time applications. TCP protocol is suitable for very less delay sensitive data packets due to the acknowledgement (ACK) scheme. This acknowledgement scheme introduces some amount of delay as receiver has to notify the sender that each packet is correctly received by sending ACK. The data packets (voice) are transmitted over the IP based network to the destination (receiver) side, and the decoding and depacketization are accomplished at the receiver. When the packet is transmitted, time variations of packets delivery may occur which are also known as jitter [3] [4]. So there is a playout buffer is used by the receiver to smoothen the speech by getting rid of delay jitter. Packets arriving after than the allotted playout era testament are discarded [5]. The principle components of a VoIP over WLAN system covers the transmission of voice is shown in figure. Figure 1.VoIP over WLANs components