IP Transport Goes Back to the Future
To Supercharge Service DeliveryOver the last decade or so IP has become the ubiquitous mechanism for supporting services and applications, this is no mean feat when we remember that ATM was designed specifically to achieve this and failed. This success has been founded on simplicity of operation, with IP/MPLS based IP transport supporting dynamic service delivery without the need for complex, centralized, management control. The network is able to self-restore in the event of failure, routing packets around a failed link or node, without the need for a central system or intelligence to pre-plan or reserve restoration paths, ports or bandwidth. However, early restoration schemes using spanning tree protocol (STP) or even rapid spanning tree (RSTP) could take considerable time to converge on an alternative path. More recently, loop-free alternative path (LFA) and remote loop-free alternative path (rLFA) have been introduced which uses a pre-configured back-up to further speed up restoration. IP/MPLS also provides a basic level of service differentiation with simple quality of service (QoS) mechanisms using diffserv and inserv in conjunction with flow control to prioritize the order of packet transmission.
This flexibility and dynamism has been perfect for supporting the “best effort” connectivity required by the vast amount of broadband services and applications that we see today. For more complex services, traffic engineering of the MPLS network could be can be achieved with RSVP-TE. Unfortunately RSVP-TE does not scale due to processing power required in the routers. And more importantly, as service needs get more stringent the complexity of setting up a network with RSVP-TE gets increasingly difficult. For services requiring deterministic behaviour, MPLS-TP provides an extremely simple to operate solution, but this is at the cost of flexibility and dynamism. MPLS-TP has to date mainly been used by operators that want to migrate to packet but keep all of the rigour of their TDM networks.
However, we are entering a new generation of services that have extremely diverse requirements. For example; remote surgery requires relatively low latency/jitter and most importantly, guaranteed always-up connectivity; autonomous cars have similar requirements, but require even lower latency; augmented and virtual reality requires high bandwidth; IoT and smart devices need massive connectivity but aren’t too concerned about latency and bandwidth; strategic and critical industries require highly deterministic performance for their operations technology (OT) but dynamic flexible performance for their (IT) network. All these services need to be supported in a highly dynamic way where users only pay for what they use and can modify their services in real time.
On its own, best-effort connectivity provided by IP/MPLS is no longer good enough to support this diverse mix of services, RSVP-TE is too complex and doesn’t scale and MPLS-TP does not provide the dynamism required. So a new set of tools are currently being developed that will allow IP/MPLS to continue to be the ubiquitous platform for transporting IP services.
The most talked about improvement is SDN. Fundamentally SDN splits the control plane from the data plane, allowing the network intelligence to be located in a centralized SDN orchestrator or controller. This orchestrator allows administrators to dynamically program the network to adapt to changing service needs and rapidly implement new services, end-to-end, across the network. Use of a path computation element (PCE) greatly enhances SDN by determining the optimal traffic path through the network. This is further enhanced by using segment routing (SR), segment routing provides the ingress router with a label stack that defines how the traffic passes through the network. This allows the centralized controller to program the behaviour of the traffic in a very predictable, deterministic way, on a per service basis.
So why do I say IP transport goes back to the future?
Well centralized management control, determinism and path computation are not a new concepts in transport networks. Centralized management from EMS’s and NMS’s have been the standard mechanisms for configuring optical transport since the early days of SDH and very early on auto-routing (i.e. path computation) was added to the NMS functionality to simplify path provisioning. As for determinism, optical networks are inherently deterministic, rigidly following set defined paths with known delays and protection times, and indeed MPLS-TP. MPLS-TP was specifically developed to replicate this determinism and centralized control in packet networks.
Optical (and MPLS-TP) networks are static and the services they transport have uniform requirements, hence the mechanisms built to control them, assume a static network and uniform service requirements. However, as mentioned previously, the new generation of services will be highly dynamic and expect a network that has the agility to support real time service modification. In addition, the network must be truly multiservice and able to support services with totally different needs. So these concepts from the past have been dusted off for the determinism and control that they bring, but they have been refreshed and revamped to operate in a dynamic, multiservice, real-time environment that IP/MPLS brings.
One final thought, as with Marty McFly and Doc, we are going even further into the past and we are starting to see the emergence one further concept which dates back right to the beginning of telecoms itself! FlexE uses the channelized TDM structure that still underpins optical transport, but was the fundamental building block for SDH and PDH and was even used in telegraph systems in the 1870s.
So it looks like this amalgamation of old and new will allow IP/MPLS to continue as the ubiquitous mechanism for supporting services and applications. Perhaps the true secret to IPs success is its flexibility and its ability to adapt and incorporate concepts from other technologies. To learn more about ECI’s Elastic MPLS technologies, download our app note here.