# Computational and Communication Infrastructure Challenges for Resilient Cloud Services
## 2 Background
### Communication Technologies for Resilience
#### 2.1.4 Programmable Network  
Programmable Network (PN) technology is a new paradigm in networking that is increasing in popularity as it allows for converting hardware problems into software problems. PN systems have great flexibility because devices and network behavior can be defined entirely by software that runs on general-purpose hardware. In a PN, engineers can re-program the network infrastructure instead of re-building it physically to provide a wide array of functions or services. Technologies in this category include Software Defined Networks (SDNs), Software Defined Radio (SDR), and Network Function Virtualization (NFV).  
SDR refers to radio communications systems where application-specific integrated circuits (ASICs) perform analog radio signal processing. In contrast, baseband digital signal processing is performed by software running on a general purpose processor (GPP) [19]. SDR enables greater resilience of wireless communication links by dynamically programming their runtime properties, such as carrier frequency, modulation type, and packet size, making them less vulnerable to physical layer attacks [20].  
SDN is an emerging architecture that centralizes network management by abstracting the data routing process (control plane) from the data forwarding process (data plane). The control plane consists of one or more devices called network controllers, which are considered the brain of the SDN network, while data plane tasks are carried out by SDN switches [21]. This innovative architecture offers the following benefits:  
* Lower cost: They typically cost less than their hardware equivalents because they run on off-the-shelf servers rather than expensive single-use devices. In addition, their deployment requires fewer resources since they allow several functions to be executed on a single server. Resource consolidation requires less physical hardware, resulting in lower overhead, power, and footprint costs.
* Greater scalability and flexibility: Network infrastructure virtualization allows network resources to be scaled up or down as needed without adding another piece of proprietary hardware. SDN offers tremendous flexibility that enables the self-service deployment of network resources.
* Simplified management: SDN results in an overall infrastructure that is easier to operate since highly specialized network professionals are not required to manage it.  
These benefits mean that SDN-based resilient networks are feasible solutions for fast disaster recovery network services at large scales [22; 23].  
NFV was proposed by the European Telecommunications Standards Institute (ETSI) as a new network architecture concept that virtualizes network node functions over open computing platforms, formerly carried out using proprietary dedicated hardware technology. NFV improves infrastructure scalability and agility by allowing service providers to deliver new network services and applications on demand without requiring additional hardware resources [24].  
NFV can be combined with SDN to create sophisticated network resilience strategies, thus simplifying resource reallocation and minimizing network recovery time. Together, these approaches can offer flexibility in terms of controlling architecture components, allowing for smart usage of the network resources, optimizing intelligent traffic steering, and increasing network reliability in general [25; 26].  
Resilient systems require higher network flexibility; hence, networks are being soft-warized via paradigms such as SDN and NFV. These solutions reduce the demand for specialized network hardware devices by extracting the inherently distributed control plane of forwarding network elements, such as switches and routers, to a logically centralized control plane.