SDN and NFV: Are they the same?

Note: This post was 1st appeared in BCS ISG Blog.

As the world progresses with unprecedented changes happening all around us, new terms/buzzwords (or abbreviations) are frequently introduced. Two such terms are SDN (or software defined networking) and NFV (or network functions virtualization), widely used within telecom, cloud and enterprise environments. Even if you are from a different field than ICT (Information and communications technology), chances are that you have heard about these terms. One of the confusions specifically associated with SDN and NFV is whether they are the same? The short answer is ‘no’. Anyway, let’s look at little closer at SDN and NFV to better understand them.

While the proper definition of NFV is available at ETSI NFV ISG (European Telecommunications Standards Institute NFV Industry Specification Group) whitepaper, the simple meaning is essentially about separating hardware from associated software in different network devices/elements. This allows for the running of different network functions (like Firewall, load balance, NAT, etc.) on cheap COTS (Commercial off-the-shelf) hardware, like switches and servers.

Going on the same viewpoint of separation, while the proper definition of SDN is available at ONF (open networking Foundation), SDN is about separating control plane from the forwarding (data) plane in a network element (ex: - router, switch, optical gear, etc.). This allows multiple forwarding planes to be controlled by a logically centralized controller or NOS (network operating system) as opposed to a single control plane (ex: - card in a router for example) and to control a single forwarding plane (ex:- line cards and back-plane) in a traditional network element (ex:- internet protocol router).

NFV creates VNFs (virtual network functions) instead of traditional PNFs (physical network functions). For example, a traditional hardware firewall (PNF) vs. virtual firewall (VNF). You need connectivity between PNFs (traditionally) or VNFs or a mix of VNFs and PNFs (in a hybrid environment) to realize an end-to-end service. This connectivity can be provided by a SDN (within a data center or between data centers). If you want to relate SDN and NFV to the ISO/OSI (International standards organization/Open systems interconnection) stack, you can think of it as bottom three layers (layer 1 to layer 3) mapped to SDN and the top four layers (layer 4 to layer 7) mapped to NFV.

Both SDN and NFV can be implemented mutually exclusive to each other. However, having them together will give better benefits to telcos (or enterprises or cloud providers) and that is why you always see SDN and NFV referred together (SDN/NFV).

If you take the broad term ‘softwarisation’, which includes SDN, NFV and cloud, it is all about different abstractions;

• NFV -> Communications abstraction
• SDN -> Network abstraction
• Cloud -> Compute abstraction 

The comparison below further explains the differences between SDN and NFV.

Parameter	NFV	SDN
Type of abstraction	Communications	Network
Key term in the abbreviation	NF virtualization	SD Networking
Architecture for	Network Elements	Network
VNF relevance	Defines VNFs	Provides connectivity between VNFs
Key focus	Services	Resources (specially network)
Optimizes	Network Functions	Network
Defined by	ETSI as a requirement	ONF as a standard