ted before they are routed to the DC/cloud. This process is based on the operator's pol- icy and prior packet classification using deep packet inspection. Con- ventional packet technologies can be employed, for example, multi- protocol label switching (MPLS) or an OpenFlow-based scheme with packet rules defined. The aggregated flow is then converted by tunable transceivers into a wavelength flow following the wavelength division multiplexing (WDM) standard. Multiple wavelength flows can be mul- tiplexed into the same fiber for transmission efficiency. O/E/O conversion is an expensive and power-intensive process that often calls for minimization in traffic engineering and network resource planning problems. In the referenced architecture, given sufficient resources, it is desirable to instantiate all the VNFs of an NF chain within a single pod. This strategy will avoid unnecessary flow traversals in the optical steering domain. In addition, resource allocation within a single pod can help reduce the complexity of resource orchestration in both the DC network and pods' resources. However, in reality, it may not always be possible to provision an entire NF chain within a single pod due to resource constraints. In a trace published by Google [5], the required resources may include computation, storage, networking, and SO on. When an NF chain has to visit multiple pods, VNF placement will affect the number of required O/E/O conversions. Figure 5.12 shows an example of two different VNF placements for three NF chains. Placement 1 is better because all the NFs of NF 5 SDN and NFV in 5G Pod(3) Pod2(2) Pod3(4) Pod4(3) NF chain Network functions (unified CPU resources) NF 1 (2) NF2 (2) NF, 4 (1) NF6(3) NF7 (1) Pod(3) Pod2(2) Pod3(4) Pod4(3) NF chain Network functions (unified CPU resources) NF (2) NF(2) NF3(1) NF4(1) NF5(1) NF6(3) NF7(1) Figure 5.12 Optical service function chaining placement problem. (a) NF placement 1 (better) and (b) NF placement 2. Chain 3 are placed in Pod3, while NF Chain 3 in Placement 2 needs to vi