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Top1. Introduction
The Internet has been a great success in the past years. Todays, the size of Internet makes the deployment of new network technology difficult (Peterson, Shenker, & Turner, 2004; Taylor, & Turner, 2004). Among several solutions, network virtualization provides an efficient way to address the conformity of the Internet (Peterson, Shenker, & Turner, 2004). And it is promoted as a powerful tool to diversify the future Internet by running multiple network services concurrently on a shared substrate network (Anderson, Peterson, Shenker, & Turner, 2004; Bavier, Feamster, Huang, Peterson, & Rexford, 2006). Therefore, as a long term solution for the future of Internet, network virtualization may play a vital role to support numerous architectures (Feamster, Gao, & Rexford, 2007). Network virtualization consists of leasing and sharing the Substrate Network (SN) infrastructure between several Virtual Networks (VNs), with the aim of increasing the profitability of the physical resources (Feamster, Gao, & Rexford, 2007). However, making better use of the underlying substrate network requires effective techniques for virtual network (VN) embedding.
Beside virtual network embedding technology, software-defined network is another technology that has received a great deal of attention recently. Software-defined network (SDN) is a promising technology that separates the control plane and data plane in networks (Voellmy, Wang, Yang, Ford, & Hudak, 2013). By separating the control plane from the data plane, switches become data forwarding devices; while network management is controlled by logically centralized servers. SDN facilitates network experimentation, and allows for optimizing routing policies. It has shown a lot of advantages in simplifying network management. For example, network administrators have central programmable control of network traffic via controllers (Voellmy, Wang, Yang, Ford, & Hudak, 2013). OpenFlow (McKeown et al., 2008) was proposed as an interface between the control and data planes in SDN. It defines the low-level packet forwarding behaviors in the data plane. Developers can program the network from a higher level without concerning the lower level detail of packet forwarding and processing in physical devices.
To be more clear, from the control network architecture, a control network can be implemented either for an in-band or for an out-of-band (Zhong, Wang, Qiu, & Li, 2016). In a SDN environment, each switch communicates with its controller via a TCP connection over a secure channel such as standard Transport Layer Security (TLS). In-band control uses the same links for both the control and data traffic. It makes the network simpler; however, the network security would be low relatively. Out-of-band control uses separate infrastructure either physical or logical to connect forwarding devices to the controller, but it suffers from the extra cost of additional hardware. Figure 1 shows in-band control network (Figure 1.a), and out-of-band control network (Figure 1.b). We utilize the in-band control network when embedding the virtual networks. This makes to consider both data and control traffic together in the term of bandwidth requirement for a virtual SDN network.
Figure 1. (a) Separate network for control and data traffic (Out-of-band control network). (b) Same network for both control and data traffic (In-band control network).