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Industry Solutions and Trends
NorthStar Controller at the MPLS/SDN World Congress
Mar 12, 2015

At the MPLS World Congress next week, we will have live demonstrations of our NorthStar Controller on our exhibition booth. Also I will present a conference paper about the benefits of having a central controller of this type for the WAN.


As shown in diagram below, NorthStar receives input from three main sources:


  • Real-time information about topology, traffic statistics and LSP status from the network itself
  • Requests from a human operator via the GUI
  • Requests via a northbound REST API


On the basis of these inputs, NorthStar makes decisions about the placement of LSPs in the network, and can create/modify/tear-down LSPs accordingly. Because the controller is coupled to the live network, it can react to changing network conditions.




The three main classes of application of interest to network operators are:


Global optimisation of the placement of LSPs in order to make most efficient use of link bandwidth around the network (also known as “bin-packing”). Because the controller has full visibility of all the LSPs needed network-wide, it can perform the bin-packing more efficiently than can be achieved with distributed path computation. This means that for a given topology, when using central path computation, more traffic can be sent through the network. During my conference talk, I will show a case-study from a real network showing the efficiency gain achieved by using central path computation rather than distributed path computation.


Because NorthStar is coupled to the live network, the placement decisions can be triggered by actual traffic levels. For example, Northstar can automatically modify the path of an LSP if the traffic volume on the LSP changes, and can even split an LSP into multiple LSPs to improve the bin-packing.


Path Computation to meet particular service requirements. An important example of this is Path Diversity. Some service providers are looking to migrate Private Circuit services from the SONET/SDH network to the packet network, where they are typically implemented as MPLS-based pseudowires. A standard service option is that a customer can request a pair of private circuits that are guaranteed to be fully diverse, including the edge nodes. This path diversity is difficult to achieve if the individual ingress nodes are computing their own paths. In the diagram below, the network has various ECMP paths, so the probability that the path computed by PE1 will not share fate with the path computed by PE2 is only 6.25%. (Of the 16 possible path-pair combinations, only one combination is completely diverse). There is not really a mechanism for PE1 and PE2 to collaborate when they compute their paths. However, the problem is easily solved by having NorthStar compute the two paths and install them onto the ingress routers.





Automated Operations. Having a central controller makes certain network operations easier. Bandwidth Calendaring allows LSPs to be automatically created and subsequently torn down at pre-determined times, or the bandwidth allocation of an LSP can be modified according to a pre-programmmed bandwidth vs time profile. If a node needs to be taken out of service for maintenance, NorthStar can automatically move the affected LSPs away, and move them back again when the maintenance is finished. In addition, NorthStar has very useful visualisation capabilites –as well being able to see the current paths of LSPs in the GUI, the past history of LSPs, including their paths, can also be seen. This is much easier than trawling through logs on the various ingress routers.


During the talk, I will also talk about the key protocol ingredients that give NorthStar visibility and control of the live network. BGP-LS gives NorthStar visibility of the topology of the network, and the TE attributes of each link (e.g. metric, bandwidth, admin groups (colours)). The Path Computation Element Protocol (PCEP) lets NorthStar know the status and attributes (e.g. the full end-to-end path) of each LSP in the network. Furthermore, the PCEP allows NorthStar to modify the paths of LSPs and to create new LSPs completely from scratch. It's important to note that the controller does not replace the network layer control plane! – IGP, BGP and MPLS protocols are still key to the operation of the network.