al communications have already enabled terabits-level high- speed transmission. One promising technology is the dense wavelength-division multiplexing (DWDM). It allows a single 5.2 Service Function Chaining fiber to carry tens of wavelength channels simultaneously, offering huge transmission capacity and spectrum efficiency. On the other hand, reconfigurable wavelength switching devices have already been widely deployed in long-haul and metro transport networks, providing reconfiguration on layer-0 lightpath topologies. We argue that optics can be used in today's DCs to the end-of-rack switches, the top-of-rack switches, as well as the servers. Although switching in the optical domain may have less agility than the packet-based approaches, it is suitable for the dynamic level required by service chains consisting of high-capacity core NFs and use of traffic aggregation. We propose that optical technology can be used to support traf- fic steering. In the following, we present a packet/optical hybrid DC architecture, which enables steering large aggregated flows in an opti- cal steering domain. Figure 5.11 illustrates an overview of the pro- posed architecture. The centralized OSS/BSS module interfaces with an SDN controller and a cloud/NFV manager. The cloud manager is responsible for cloud resource allocation and automating the provisioning of VMs for VNFs. It also includes an NFV management module that handles instantiation of the required VNFs while ensuring correctness of configuration. The SDN controller can be a part of the cloud management subsys- tem or a separate entity. The SDN controller and cloud/NFV manager perform resource provisioning. On the southbound interface, the SDN controller uses optical circuit switching to control the network ele- ments. This interface can be realized using OpenFlow V. 1.4, which has an extension for optical circuit configuration. To perform service chaining, the OSS/BSS module needs to request VNFs and network resources and the policies for resource allocation. The SDN c