Software Defined Networking (SDN) emerged in recent years to fundamentally change how we design, build and manage networks. To maximize the network utilization, its control plane needs to frequently update the data plane via flow migration as the network conditions change dynamically, which is known as network update. Network Function Virtualization (NFV) addresses the problems of traditional expensive hardware appliances by leveraging virtualization technology to implement network functions in software modules (middleboxes). These software modules, also called Virtual Network Functions (VNFs), are provisioned most commonly in modern networks to demonstrate their increasing importance. The technical combination of SDN and NFV enables network service providers to pick service locations from multiple available servers and maneuvers traffic through appropriate VNFs, which is known as VNF deployment. A service chain consists of multiple chained VNFs in some order. VNFs are executed on virtualization platforms, which makes them more prone to error compared with dedicated hardware. As a result, one important issue of service chain is its reliability, meaning that each type of VNF in a service chain acts properly on its function, which is known as service chain resilience. This dissertation lists our research on the above three mentioned topics in order to improve the network performance. Details are as follows: 1. Network Update: SDNs always need to migrate flows to update the network configuration for a better system performance. However, the existing literature does not take flow path overlapping information into consideration when flows’ routes are re-allocated. Consequently, congestion happens, resulting in deadlocks among flows and link resources, which will block the update process and cause severe packet loss. We propose multiple solutions with various kinds of leisure resources in the network. 2. VNF Deployment: We focus on the VNF deployment problem with different settings and constraints, including: (1) network topology; (2) vertex capacity constraint; (3) traffic-changing effect; (4) heterogeneous or homogeneous model for one VNF kind; (5) dependency relations between VNFs. We efficiently deploy VNF instances and at the same time make sure that the processing requirement of all flows are satisfied. 3. Resilient Service Chain Management: One effective way of ensuring VNF robustness is to provision redundancy in the form of deploying backup instances besides active ones. In order to guarantee the service chain reliability, we consider both the server resource allocation and the VNF backup assignment. We aim at minimizing the total cost in terms of transmission delay and rule changes. / Computer and Information Science