# Comprehensive Comparison of VNE Solutions Based on Different Coordination Approaches
## 1 Introduction
Ensuring security robustness--Data integrity and transactional privacy are two of the most important ingredients of communication trustworthiness. This notion applies to the fullest regarding virtualization environments, where a multitude of VNs can be layered over the same physical medium. Early attempts have been made by researchers in order to introduce security aware VNE algorithms, which would involve both resource and security restrictions, by incorporating specific sets of security rules [17]. Achieving VN survivability--A network application can acquire characteristics of added resilience provided that the underlying physical network adopts survivability  
Figure 1: Revised Service Provider business model. mechanisms, applied either to the entirety or to specific parts of the SN. These mechanisms would take effect during the Virtual Network Request (VNR) analysis and are meant to calculate the appropriate fallback resources in order to achieve the desired resilience. These backup resources are materialized as additional substrate nodes, substrate links or a mixture of both and are assigned to a specific VNR until the end of its lifecycle. In the same sense, fault-sensitive applications also require nonnegotiable transparency while transitioning from the primary to the backup resources and vice versa, thus, rendering the recovery from any kind of failure seamless to the application users [18, 19]. Guaranteeing Quality of Service (QoS)--In the case of QoS-specific VNRs, a SP may choose an entirely different approach for handling the submitted request depending on the situated scenario. In this context, a telecommunications service, which is likely susceptible to quality discrepancies, may impose configuration variations and weighted indices regarding the respective constraints and metrics [18, 19]. Maximizing economical profit--VNE is a problem that needs to be solved by taking into account its real life proportions as well. A VNR will almost always represent a request for a commercial service, the satisfaction of which would most certainly involve the lease of expensive and finite networking and computational resources for a certain period of time, from a single or several InPs. Under such circumstances, all the links of this commercial chain may end up spending a substantial share of capital in order to materialize the VN mappings required by the VNR. As a result, a popular approach and mainstream VNE goal is the maximization of revenue [20]. This objective is directly proportional to the minimization of the embedding cost. Arbitrary satisfaction of service requests may only lead to poor management of networking and computational assets, thus, wasting financial resources and temporal and energy capital. The customized dynamic allocation of virtual resources over existing bare metal environments can maximize the benefits gained from the physical underlay by all the counterparts, from the InP to the end user. Nevertheless, the achievement of the desired optimality may be a rather complex endeavor and, at the same time, the key to the success of VNE. VNE deals with the assignment of the demanded resources of virtual nodes and virtual links that constitute a VN. The Virtual Node Mapping (VNM) and Virtual Link Mapping (VLM) subproblems deal with the allocation of the computational demands over substrate nodes and the synthesis of virtual links into physical paths, respectively. Both are considered mathematically complex [21], and the algorithms used to calculate their solutions can deal with them separately or adopt a form of coordination (see Section 3). Depending on the coordination strategy, the embedding results may vary considerably, and the satisfaction of the optimization objective can be jeopardized.