NFV Architecture

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NFVI - Network Functions Virtualisation Infrastructure

NFVI Consists of all resources required to gain virtualisation. NFVI can span across many locations, e.g. a part of the infrastructure could be in city A and another at city B to enable geo-redundancy.

A location where NFVI node is deployed is called NFVI-PoP ( NFVI Point of Presence). NFVI-PoP may contain one or more NFVI nodes and network elements. VNFs can be in the same or different NFVI-PoPs.

It includes

1. Hardware Resources

CPU, Memory ( RAM ), Storage, Routers, Switches, Cables and all kinds of hardwares. It will also include hardware to provide security, encryption and decryption, packet switching, accelerated packet forwarding etc.

2. Virtualisation Layer

Virtualisation Layer consists for hypervisors like esxi, kvm, xen etc . The hypervisor has complete  control over the physical hardware resources and abstract them for the Virtual Machines. Virtual machines are provided with virtual resources, hypervisor converts the instructions on virtual resources to physical resources. It decouples the VNF from the hardware and also provides isolation between VNFs.

3. Virtual Resources

Virtual Machines are provided with virtual resources. The virtual machine will treat the virtual resources as physical resources and perform necessary actions on them. The hypervisor will map the virtual resources to physical resources. This includes virtualised compute , network and storage pools.

VIM - Virtualised Infrastructure Manager

Virtualised Infrastructure Manager is a cloud management software used to control and manage the virtual resources, Virtual resources include VMs, NFVI resources allocated to VM  and the interactions between VMs and NFVI. Few functionalities of VIM are as follows

• Management of computing, storage and network resources allocated to the VM
• Allocation of VMs to resources i.e. allocate a particular VM on a particular compute with a specific storage
• Modify resources allocated to VM
• Collect VM and NFVI related statistics.

VMWare - ESXI and Openstack are examples of VIM.

VNF - Virtualised Network Function

A VNF is virtualisation of the legacy network function. A VNF could be a single VM or it could be distributed across multiple VMs. In most cases a VNF will comprise of several components, each component hosted in a single VM, for performance and scalability.

For e.g., traditionally a network function (NF) like MME will have all components distributed in a single Chassis and working as 1 unit. However, in a virtualised environment, MME could be divided into several components like s1MME component, gtpc component, core component etc , each of them being hosted in a separate VM. All these VMs together will for a single MME VNF.

VNF Manager - Virtualised Network Function Manager

A VNF manager manages the state, lifecycle and resources of one or more VNFs. It is responsible for instantiation, update, query, scaling,healing,  termination etc of the VNFs. It can also create and manage VIM resources like tenant, images, volumes, networks, flavors which can later be used as part of the VNF creation. A VNFM can talk directly to the VIM and creates the VNF. In cases where the VNF hosts a complex application like Mobile Packet Core or IMS, VNFM typically talks to the Element Manager ( explained in the next section ) to carry out the required actions.  A single VNF Manager may manage multiple VNFs, multiple VNFs across multiple VIMs or multiple homogenous and heterogenous clouds (VIMs).

E.g. Tacker - an open source VNFM

EM - Element Manager

Element Manager or EM manages the VNF. Vcenter for VMWare ESXI and Virsh for KVM perform EM functionalities as well.

A VNFM can manage external resources and states of VM but it cannot access any information of the application running inside the VM. Element Manager bridges that gap. Element manager is generally created by the VNF team and can access the state and resources of the VNF. EM can request VNFM to carry out various VNF related action by evaluating the different policies based on the VNF state. EM also handles the FCAPS statistics from VNF required by the OSS/BSS elements.

OSS/BSS

Operations Support System and Business Support Systems collect the various FCAPS statistics and traps. Operators can push various policies to the NFV Orchestrator based on these policies.

NFV Orchestrator

The NFV Orchestrator consists of various catalogues and designs related to networks and VNFs. As per the ETSI MANO architecture, the NFVO can talk to the VIM directly and can do resource checks and do resource allocations like VNF placements. The NFVO can manage more than one VNFM and can manage multiple VIMs. Since NFVO will have collective information from multiple VIMs, it can coordinate the resource allocation across these VIMs.  The VNFM creates the networks, storage, VNFs and allocates resources to VNFs based on the input received from NFVO. The VNFM can only bring up different VNFs but cannot define the service chaining. It is the NFVO which does the  service orchestration.

E.g. Tacker - an open source NFVO