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Development of Voice Call Transfer Service between Android Smart Phone and Tablet

Everyone necessitate communication technology in this information era. By use of modern technology, everyone should prefer wireless service without using bundle of wires. Colleges, shopping malls, corporate offices, coffee shops, construction buildings and restaurants provide Wi-Fi service to customers. Wi-Fi service allows data and voice transmissions over connected devices in same network. Proposed paper presents development of voice call transfer service that processes incoming telephone call which uses Wi-Fi as communication medium for voice transmission between smart phone and tablet. The proposed method allows real time communication transferred over wifi using IP between smart phone and tablet at no cost. Wi-Fi enabled smart phone and tablet are connected to the router or wifi access point to provide communication between caller and tablet user. Proposed paper develops cost effective, easy and reliable voice communication over Wi-Fi which provides good and comfort experience to user. Key-words: Wi-Fi Service, Voice Transmission, Real Time Communication, Router, Voice Call Transfer Service.


Introduction
Telecommunication has more advanced in most businesses organizations which emphasizes press of simple button makes communication for developing economy. Hence, it is necessary to find solutions in cheap and affordable must be sought. Reliable communication has posses a great demand because of its secured and easy usage. Even though it is a simple and closed environment, there is a

Literature Review
Communication is very important part in our daily life. Vast improvement in technology leads convenient and efficient way of communication. Large organizations like educational institutes, corporate offices, construction sites plays fabulous role to support required communication among all employees. So it is necessitated to develop application which is easy to deploy, run, and access. Many organizations furnish Wi-Fi service for all employees to supply internet connection. By using this, one can connect laptop, tablet or smart phone to Wi-Fi router and get internet connectivity [6]. In recent surveys, Wi-Fi service was predicted as growing to 109 percent between 2011-2016 in automotive applications, 39 percent in health, fitness and medical applications, 25 percent in smart meters [7]. Hence usage of android smart phones has increased to hundreds of millions in more than 190 countries throughout world. Taking into consideration of growth in Wi-Fi as well as in android, proposed paper develops android mobile application for voice transferring through Wi-Fi network. There are several use cases addressed by different smart phones for voice communication.
Two-way radio transceivers allow peers in same range establishes voice communication without having any additional infrastructure [12]. This is very useful in scenarios of no cellular network coverage or when users cannot afford cost of an ongoing call for unlimited period of time [13]. Even though smart phones have great connectivity with Wi-Fi or Bluetooth, till now no research provided voice call transferring service through mobile application. Main objective of proposed application resolves this problem by transferring incoming caller voice to tablet connected in same Wi-Fi range.

Call Receiving
Android telephony API provides service for incoming telephony calls. Phone state listener provides listening states for incoming calls. When incoming call arrives on smart phone, it will automatically detected by the proposed application. Figure 3 shows process of telephony incoming call in android programming.

Wireless Communication
Mainly, proposed application development consists of two processes: peer discovering and connecting. Peer discovering process uses registration process for every user in Wi-Fi range.
Whenever Wifi is enabled, the users need to be registered with names. After user registration, update button will update all registered users and shown below update button. Every user has been watched by other users in network. Choosing required user for voice call transfer by selecting check button of one of registered users. Broadcasting voice communication will be enabled between caller and selected user. Figure 4 shows wireless communication process in android programming.

Transfer Voice through Network
Smart phone will detect the registered user with its IP address. The IP address of user is recognized by auto discovery of IP address using WiFi manager API. Whenever users are added, those are updated with their IP addresses. Android audio manager API provides read and write methods to send encoded voice and receive decoded voice respectively. Real time voice For this, UDP is used to provide socket based communication through packets. As and when Android devices starts sending voice call, the voice codec compress and encode the voice call into frames and are stored into a buffer. This voice will be processed by UDP protocol and is sent over Wi-Fi.
At the receiving end, when the tablet received call through Wi-Fi, user get options like accept and end call. Communication is enabled when tablet user accept call. Every time voice is received by audio encoder, it is stored in buffer and sent as packets to destination. At destination device, received packets are given to audio decoder which decodes received voice. This decoded voice is stored in a dynamic buffer. It will be identified and played by android media API through GUI of android. In the same manner, the communication from tablet is sent to the smart phone. Figure 5 shows voice processing between two users.

 Voice Recording
Raw voice data from microphone is encoded by android audio record API (Application Program Interface). To record and encode raw voice, 8 Kbps is used as sampling rate, 16 bit PCM (Pulse Code Modulation) is used as audio encoding format and 4096 bytes is used as buffer size.

 Voice Encoding
Audio record in android audio manager API is used for real time audio processing. Figure 6 shows real time audio processing for encoding and decoding in android programming. It is used for illustrate programming and compilation report for registration of users in same Wi-Fi network through Android Wi-Fi and Datagram socket APIs. Update user will update all users registered to same Wi-Fi network.

Conclusion
Proposed application has developed various modules involved in transferring voice call through Wi-Fi. Main work done is transferring voice in form of packets through UDP socket.
Developed application is user friendly since each user can register with their names without familiar with any technical knowledge about wifi or IP address. This free wireless voice transfer service is enabling not just free calls but also providing more advantageous and rich features and more flexible services. Although challenges stay behind, proposed application will play key role in businesses communications, small and big offices, schools, homes, construction sites etc. As per cost factor, there is no need of internet charges and telephony call charges.