Back in the old days, Network Service Assurance probably had a different meaning than it might today.
Clearly it’s assurance of a network service. That’s fairly obvious. But it’s in the definition of “network service” where the old and new terminologies have the potential to diverge.
In years past, telco networks were “nailed up” and network functions were physical appliances. I would’ve implied (probably incorrectly, but bear with me) that a “network service” was “owned” by the carrier and was something like a bearer circuit (as distinct from a customer service or customer circuit). Those bearer circuits, using protocols such as in DWDM, SDH, SONET, ATM, etc potentially carried lots of customer circuits so they were definitely worth assuring. And in those nailed-up networks, we knew exactly which network appliances / resources / bearers were being utilised. This simplified service impact analysis (SIA) and allowed targeted fault-fix.
In those networks the OSS/BSS was generally able to establish a clear line of association from customer service to physical resources as per the TMN pyramid below. Yes, some abstraction happened as information permeated up the stack, but awareness of connectivity and resource utilisation was generally retained end-to-end (E2E).
But in the more modern computer or virtualised network, it all goes a bit haywire, perhaps starting right back at the definition of a network service.
The modern “network service” is more aligned to ETSI’s NFV definition – “a composition of network functions and defined by its functional and behavioral specification. The Network Service contributes to the behaviour of the higher layer service, which is characterised by at least performance, dependability, and security specifications. The end-to-end network service behaviour is the result of a combination of the individual network function behaviours as well as the behaviours of the network infrastructure composition mechanism.”
They are applications running at OSI’s application layer that can be consumed by other applications. These network services include DNS, DHCP, VoIP, etc, but the concept of NaaS (Network as a Service) expands the possibilities further.
So now the customer services at the top of the pyramid (BSS / BML) are quite separated from the resources at the physical layer, other than to say the customer services consume from a pool of resources (the yellow cloud below). Assurance becomes more disconnected as a result.
OSS/BSS are able to tie customer services to pools of resources (the yellow cloud). And OSS/BSS tools also include PNI / WFM (Physical Network Inventory / Workforce Management) to manage the bottom, physical layer. But now there’s potentially an opaque gulf in the middle where virtualisation / NaaS exists.
The end-to-end association between customer services and the physical resources that carry them is lost. Unless we can find a way to establish E2E association, we just have to hope that our modern Network Service Assurance (NSA) tools make the yellow cloud robust to the point of infallibility. BTW. If the yellow cloud includes NaaS, then the NSA has to assure the NaaS gateway, catalog and all services instantiated through the gateway.
But as we know, there will always be failures in physical infrastructure (cable cuts, electronic malfunctions, etc). The individual resources can’t afford to be infallible, even if the resource pool seeks to provide collective resiliency.
Modern NSA has to find a way to manage the resource pool but also coordinate fault-fix in the physical resources that underpin it like the OSS used to do (still do??). They have to do more than just build policies and actions to ensure SLAs don’t they? They can seek to manage security, power, performance, utilisation and more. Unfortunately, not everything can be fixed programmatically, although that is a great place for NSA to start.
Perhaps if the NSA was just assuring the yellow cloud, any time it identifies any physical degradation / failure in the resource pool, it kicks a notification up to the Customer Service Assurance (CSA) tools in the OSS/BSS layers? The OSS/BSS would then coordinate 1) any required customer notifications and 2) any truck rolls or fixes that can’t be achieved programmatically; just like it already does today. The additional benefit of this two-tiered assurance approach is that NSA can handle the NFV / VNF world, whilst not trying to replicate the enormous effort that’s already been invested into the CSA (ie the existing OSS/BSS assurance stack that looks after PNFs, other physical resources and the field workforce processes that look after it all).
I’d love to hear your thoughts. Hopefully you can even correct me if/where I’m wrong.