The 4th generation of cellular system (LTE) does not inherit the traditional voice (circuit-switched) capabilities from its predecessors. Instead it relies on its high speed packet-switched core network with IMS (IP Multimedia Subsystem) for voice capabilities. Even though there are temporary solutions available until LTE gets its full deployment and coverage, operators are looking for a long term solution known as VoIMS which uses VoIP with SIP protocol for voice in the LTE network (VoLTE) through the IMS domain. The scope of this thesis work is to design, implement and verify the working of the core network for an LTE type software defined radio (SDR) testbed which is able to initiate, maintain and terminate voice and data connections. First step in this regard is to search and select the tools, programs and technologies that fulfil the network requirement in terms of network performance and user satisfaction. Next is to build, configure and verify the network operations of the designed network.As SDRs are used for testing purposes, the core network is also designed in correspondence to that, i.e., it is a test (lab) core network with configurations that are simple to implement and do not require coding implementation. The core network makes use of the virtualization technology and is realized with the help of open-source solutions, i.e., protocols and technologies that are customizable as required and does not require licensing for their use. These functionalities are implemented with the help of OpenSIPS, an open-source SIP server, DHCP and DNS servers. Demonstration of the core network verifies that successful voice and video call can be made between registered users on two different networks, running VoIP client software on different operating system platforms. The core network provides features such as voice, video, instant messaging, presence, dynamic IP assignment, IP address to name resolution and mobility.
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