High-level VNF Descriptors using NEMO

Currently, there is a lot of on-going activity to deploy NFV in the network. From the point of view of the orchestration, Virtual Network Functions are blocks that are deployed in the infrastructure as independent units. Following the reference architectural model proposed in , VNFs provide for one layer of components (VNF components(VNFCs)) below, i.e. a set of VNFCs accessible to a VNF provider can be composed into VNFs. However, there is no simple way to use existing VNFs as components in VNFs with a higher degree of complexity. In addition, Network Service Descriptors (NSD) and VNF Descriptors (VNFDs) specified in and used in different open source MANO frameworks are YAML-based files, which despite being human readable, are not easy to understand. On the other hand, there has been recently an attempt to work on a modelling language for networks or Network Modelling (NEMO) language. This language is human-readable and provides constructs that support recursiveness. In this draft, we propose an addition to NEMO to make it interact with VNFDs supported by a NFV MANO framework. This integration creates a new language for VNFDs that is recursive, allowing VNFs to be created based on the definitions of existing VNFs. This draft uses two example formats to show how low level descriptors can be imported into NEMO. The first one is the format used in the OpenMANO framework. The second one follows strictly the specifications provided by ETSI NFV ISG in . Conceptually, other descriptor formats like TOSCA can also be used at this level.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in .

Virtual network function descriptors (VNFDs) are used in the Management and orchestration (MANO) framework of the ETSI NFV to achieve the optimal deployment of virtual network functions (VNFs). The Virtual Infrastructure Manager (VIM) uses this information to place the functions optimally. VNFDs include information of the components of a specific VNF and their interconnection to implement the VNF, in the form of a forwarding graph. In addition to the forwarding graph, the VNFD includes information regarding the interfaces of the VNF. These are then used to connect the VNF to either physical or logical interfaces once it is deployed. There are different MANO frameworks available. For this draft, we will first concentrate on the example of OpenMANO, which uses a YAML representation similar to the one specified in . Then we will provide an example using the exact format specified in .

Taking the example from the (public) OpenMANO github repository, we can easily identify the virtual interfaces of the sample VNFs in their descriptors:

In this example we consider the VNF represented in Figure 6.4 of . Its internal diagram, including a VNF component, is represented in Figure . A YAML representation of the VNF Descriptor is reported in Figure . The topology of the interconnection of VNFs is expressed by using the abstraction of Virtual Links, which interconnect Connection Points of the VNFs. The Virtual Links are described by Virtual Link Descriptors (VLD) files. An example YAML representation of the Virtual Link VL1 in the example VNF is reported in Figure . In order to understand the topology, a (potentially large) set of VNFD and VLD files needs to be analysed. For a human programmer of the service, this representation is not friendly to write and very hard to read/understand/debug.

The Network Modeling (NEMO) language is described in . It provides a simple way of describing network scenarios. The language is based on a two-stage process. In the first stage, models for nodes, links and other entities are defined. In the second stage, the defined models are instantiated. The NEMO language also allows for behavioural descriptions. A variant of the NEMO language is used in the OpenDaylight NEMO northbound API. NEMO allows to define NodeModels, which are then instantiated in the infrastructure. NodeModels are recursive and can be build with basic node types or with previously defined NodeModels. An example for a script defining a NodeModel is shown below:

In order to integrate VNFDs into NEMO, we need to take into account two specifics of VNFDs, which cannot be expressed in the current language model. Firstly, we need a way to reference the file which holds the VNFD provided by the VNF developer. This will normally be a universal resource identifier (URI). Additionally, we need to make the NEMO model aware of the virtual network interfaces.

As explained in the introduction, in order integrate VNFDs into the NEMO language in the easiest way we need to reference the VNFD as a Universal Resource Identifier (URI) as defined in RFC 3986. To this avail, we define a new element in the NodeModel to import the VNFD:

VNFD ;]]>

As shown in , VNFDs include an exhaustive list of interfaces, including the interfaces to the management network. However, since these interfaces may not be significant for specific network scenarios and since interface names in the VNFD may not be adequate in NEMO, we propose to define a new entity, namely the ConnectionPoint, which is included in the node model .

; ConnectionPoint at VNFD:; ]]>

Once these two elements are included in the NEMO language, it is possibly to recursively define NodeModel elements that use VNFDs in the lowest level of recursion. Firstly, we create NodeModels from VNFDs:

Then we can reuse these NodeModels recursively to create complex NodeModels:

This NodeModel definition creates a composed model linking the sample_vnf created from the VNFD with a hypothetical shaper_vnf defined elsewhere. This definition can be represented graphically as follows:

In ETSI NFV, a network service is described by one or more VNFs that are connected through one or more network VNFFGs. This is no more than what is defined in the composed NodeModel shown if . By using NEMO, we provide a simple way to define VNF forwarding graphs (VNF-FGs) in network service descriptors in a recursive way.

With the strategy defined in this document, we are able to link a low-level VNF description into a high-level description language for networks like NEMO. Effectively, we are introducing recursiveness in VNFDs, allowing complex service descriptors to be built by reusing previously tested descriptors graphs as building blocks. Although we have used the OpenMANO descriptor format in this document, other descriptors and concepts (i.e. as those used by TOSCA) can also be used as the lowest level in this extension to the NEMO language.

This draft includes no request to IANA.

The VNFD construct as IMPORT allows referencing external resources. Developers using it in NEMO scripts are advised to verify the source of those external resources, and whenever possible, rely on sources with a verifiable identity through cryptographic methods.

This work has been partially performed in the scope of the SUPERFLUIDITY project, which has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No.671566 (Research and Innovation Action).