The traditional network devices are defined on a rudimentary architecture, because of that, both the hardware and software are customized and firmly integrated. In contrast, NFV allows software developed by the vendors to run on generic shared hardware, creating an ease of management. Understanding the NFV framework enables readers to open their eyes to the flexibility, efficiency, ease of management and freedom of choice that NFV offers.
VNFs can be from any vendor as per the choice of service providers that best suit their needs. In order to implement this freedom of choice it is needed that a standardized method of communication between the VNFs is created, as well as a way to manage them in the virtual environment.
The standardized framework ensures that the VNF deployed is not tied to specific hardware and does not need to be specially tailored for any environment. It needs to offer vendors a reference architecture that they can follow uniformity and consistency in the deployment methodologies of any VNF they implement. Furthermore, the dependency on any vendor needs to be eliminated. This framework provides the foundations that allow the VNFs, hardware, and the management systems to work seamlessly within the well-defined boundaries.
The three main component of NFV framework, when combined, deliver virtualization of network functions. Let’s take a look at them:
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Network Function Virtualization Infrastructure (NFVI)
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Virtualized Network Function (VNF)
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NFV Management and Orchestration (MANO)
Infrastructure Layer:
Virtual networks functions need a virtual hardware to run on which is further emulated by software resources run on actual physical hardware, in the ETSI NFV framework this takes place in NFVI layer, it comprises of:
- Hardware resources(Physical)
- Virtualization layer
- Virtual resources
ETSI framework divides the hardware resources into three main categories –
- Computing
- Storage
- Network
Hardware Resource layer:
This is where the actual hardware resides, it includes computing, storage and network. Providing the hardware for storage, processing and connectivity to VNFs via virtualization layer. Computing and storage resources are commonly used in a pool it includes the memory and the CPU. The network resource comprises of network interface cards and ports that can be used by the VNFs e.g. router, wired or wireless network. What sets NFV apart is that no hardware is purposely built for any particular network function or none of it is vendor locked, instead it is a generic hardware device also known as commercial of the shelf (COTS).
Virtualization Layer:
This is where the separation of software from the hardware happens for network functions (i.e., VNF), it provides them isolation from other VNFs and acts as an interface to the physical hardware. The virtualization layer is a part of NFVI. It connects directly with the pool of hardware devices (compute, storage and networking), making them available to VNFs as a virtual machine. The virtual machine delivers the virtualized computing, storage, and networking resources to the software that it hosts (VNF in this case) and presents these resources to the VNF as if they were dedicated physical hardware devices.
Virtual Resources:
Once the virtualization layer abstracts the hardware resources (compute, storage network) it is made available as virtual resources. The resultant virtualized resources are finally made available to the VNFs that will be using them.
VIM:
The functional block, VIM defined by ETSI is Virtualized infrastructure manager, this block is a part of Management and Orchestration (MANO), VIM has been delegated the responsibility to manage the elements in NFVI i.e the hardware, virtualization layer, and virtualized hardware resources, VIM has the complete visibility into the operational attributes of hardware resources, such as health status, availability and power management, furthermore, VIM also has the ability to see the performance attribute of these hardware resources e.g. the statistics for utilization. VIM apart from managing the virtualization layer has the ability to influence and control how the virtualization layer uses the hardware. The ETSI framework allows a Single VIM to control multiple NFVI functional blocks, and multiple VIMS to control different hardware resources.
Virtualized Network Functions (VNF) Layer:
This is where implementation of virtualization of network functions takes place. The VNFs are expected to be unaware of the fact that the hardware it is running on is actually a virtual machine, therefore its behaviour is expected to be similar to the physical implementation of network function.
Element Management: Performs an assisting function, it serves as a layer of interaction between the devices performing network functions and network management system.
Because VNF manager had the responsibility for the FCAPS of the VNFs , it either manages it directly or uses the Element Manager (EM) functional block.
FCAPS is an abbreviation for five management parameters:
- Fault
- Configuration
- Performance
- Accounting
- Security
The service that is being virtualized can require various combinations of VNFs or can run on a single VNF. When a group of VNFs are implemented and do not have any inter-dependency they are known as VNF set, they collectively offer their part of functionality but implement their functions independently. However, if the Network service to be implemented where the data stream needs to travel through a specific sequence then the connectivity between the VNFs need to be defined, it is referred as service chaining or VNF-Forwarding Graph.
OSS/BSS:
OSS/BSS are Operational and billing support system of an operator.
OSS deals with the following main functions:
- Network management
- Fault management
- Configuration management
- Service management
Whereas, BSS deals with:
- Customer management
- Product management
- Order management
The functional block OSS/BSS brings value to management and has a place in the framework. The NFV framework defines the reference points between the existing OSS/BSS and NFVO and defines NFVO as an extension of the OSS/BSS to manage the NFV deployment without changing the roles of OSS/BSS in today’s networks.
NFV framework summary (putting it all together)
The purpose of defining the framework, detailed individual functional blocks and the reference points is to eliminate (practically speaking, improve) interoperability challenges and standardize the implementation of network virtualization. The need and scope of each of these blocks are defined in detail by the framework.
Overall, creating standards in virtualization has simplified the usability of VNFs in a way that is independent of the vendor supplying them. ETSI framework has created homogeneous and reusable NFV solutions as it continues to develop.
