YANG Models DEVICE efficiently VNF PNF MODELS VNF Virtual Network Function PNF Physical Network Function FIGURE 3.6 YANG and NETCONF. pushed to a forwarding device for implementation. Figure 3.6 illustrates how YANG models can be designed and stored in a catalog. (AT&T has created a YANG model design studio to help a service designer create the YANG models for their service.) The model can then be pushed to the VF via a protocol called NETCONF (IETF). NETCONF is defined to install, manipulate, and delete the configuration of network devices via remote procedure calls (RPC). YANG models are extensible to many software models for more abstracted layers of network functions. As Figure 3.7 depicts, we can use YANG to define the data model for a service at the device layer (e.g., single-forwarding device), network layer (e.g., VLANs across a metropolitan area network [MAN] or wide area network [WAN]), service layer (end-to-end service definition like Ethernet WAN), and finally the API layer, which defines the software interface we can expose to request the end-to-end service for a customer. Two additional workload types can be found in VNF implementations, but to a lesser degree: Signal processing workloads-defined as workloads related to digital signal processing (such as Fast Fourier Transform [FFT] decoding/encoding in a Cloud Radio Access Network [C-RAN] base band unit [BBU] [Jun Wu]). These are typically very CPU intensive and highly delay sensitive. In previous discussions, we have tended to characterize media trans- coding as a signal processing workload, although given the definitions in this specification, it would appear that transcoding has more in common with data plane workloads involving encryption. It is expected to have increased CPU utilization compared to other data plane workloads, but is no more delay sensitive than general packet forwarding. Storage workloads-defined as workloads involving disk storage, subdivided in the specifica- tion into intensive and nonintensive. BUSINESS SUPPORT SYSTEMS API