As the concept of NFV is introduced in EPC the open source software instances

As the concept of nfv is introduced in epc the open

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and Mobility management entity (MME). As the concept of NFV is introduced in EPC, the open source software instances for realizing the virtualized version of many of these components has been developed. e ) Virtualization of content delivery networks In content delivery networks, deploying cache nodes for enhancing the quality of multimedia services is pop- ular. This strategy brings some disadvantages such as wastage of the dedicated resources. These shortcomings can be mitigated by using the concept of NFV in CDNs [6] . f ) Network function virtualization as a service NFV infrastructure, its platform and the VNF in- stances can be provided as a service by a service provider similar to the cloud service model [7] . III. Service Function Chaining A network service is a complete end-to-end function- ality offered to users by network operators. It usually con- sists of several Service functions (SFs) chained in order.
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Optimal Network Function Virtualization and Service Function Chaining: A Survey 707 For example, in a “Network protection” service, required service functions may be firewall, DPI and virus scanner. In a formal definition, each service function (also is called network function), is responsible for a specific processing on the received packets. By definition, a service function chain is a sequence of service functions that must be executed in a determined order as the result of classification and/or policy, and Ser- vice function chaining (SFC) is the mechanism of build- ing service function chains and forwarding packets/flows through them. To design an optimized, dynamic and au- tomated SFC framework, the IETF (Internet engineering task force) has taken steps by defining a formal architec- ture for SFC on top of the ETSI NFV architecture. The SFC architecture [8] has three different planes as shown in Fig.3. Fig. 3. Architecture of Service function chaining [8] The management plane consists of SFC manager, SF Path manager and service function manager. They man- age the installation, maintenance and termination of ser- vice functions. The data plane consists of classifier and service func- tions (Fig.3). The classifier identifies and classifies traffic before forwarding it into the Service function path (SFP). The path between classifier and service functions is set up and managed by the control plane that includes policy controller, SFC controller, SFP controller, and user pro- file. First, the SFC controller generates or selects a spe- cific service function chain using the result of analyzing incoming packets at the ingress classifier. The user pro- file stores user preferences and subscription information; where, an appropriate service function chain is allocated with referring to both. The SFP controller determines one among the relevant service function paths within the ser- vice function chain, satisfying capacity and QoS require- ment of service functions and their connecting links, and then places service functions in the network. Last, the pol- icy controller is used to maintain SFC policy tables that represent forwarding paths.
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