WAN SDN Controller Deep Dive

My previous post, the overview of WAN SDN Controller is explained. So, in current post i will describe the functional element of WAN SDN Controller and it's correlation with some use-cases.

If we refer to Verizon SDN NFV Reference Architecture

Service Management

The Service management function for all aspect of service installation and management. It is hiding the complexity of the network since the resources are been abstracted, hence the northbound application/orchestration function can call to Service management API to create a complex services, which WAN connectivity only one of its component. let's say an orchestrator want to create DC interconnect which spanning from one DC to another. The orchestrator can call API to DC SDN controller to spin-up the VMs and create interDC connectivity with VXLAN. In parallel orchestrator tell WAN SDN Controller to prepare WAN connectivity from IP and Optical networks between the DCs

Resource Management and Optimization

This function enables northbound systems to create, modify or delete resources. It provides functions like optimal path selection, tunnel load balancing, bulk optimization, traffic reroute for maintenance actions, etc. The Resource Management function can use the statistics collected by the SDN Controller itself or it can interface with standalone analytics solutions that may trigger optimization actions.

The use case example are:

• Path(could be MPLS LSP or Optical Cross-Connect) creation and modification 
• Optimised the path based on certain algorithm, hence not following IGP mechanism normally based on cost, this could unlock stranded bandwidth form underutilized link connection which neglected by normal IGP path selection mechanism.
• Path optimization based on certain internal or external trigger. ie: if the link utilisation of certain link reach certain threshold the path that using this particular link is become subject to be optimised.
• FireBlanket, the WAN SDN controller can push a certain network policies to all IP devices in network perimeter based on external system intelligence that detected potential anomaly like DDoS attack.

Statistics and Topology

An SDN Controller provides several basic functions, such as statistics collection (per service and/or resource) and topology discovery. This information is used as input to the Resource Management function and can also be exposed to northbound systems via ReSTful APIs. 

Some of use case that can use this functional elements are:

• Network Statistic Data Warehouse, the statistic of the network can be exported to external data warehouse to be used for certain analytics.
• Offline Traffic Engineering, A tools can be developed to simulate certain scenario in the network by taking the advantage of statistic and topology information from this element 

Forwarding Rules Manager

When the network contains white boxes, a Forwarding Rules Function is required to define the exact set of forwarding rules to be pushed to those white boxes. The Forwarding Rules Manager takes into account topology information and the service and resource related inputs from the Service Management and Resource Management functions.

Adaptation

The adaption function translates abstract, device-independent data models that are used by the Service Management and Resource Management functions to device-specific data models. These device independent data models are service-oriented models that are rendered in YANG. 

South-bound protocol stacks

Depending on the network element and the required action, different protocols may be used. OpenFlow is one of the protocols of choice for managing white boxes. The choice of the south bound protocol depends on the use case and will also require additional adaptations / extensions. NETCONF (RFC 6241) is emerging is the primary candidate for provisioning network functions in general. PCE Protocol (PCEP, RFC 5440) is the primary protocol for path setup in RSVP-TE MPLS networks. PCEP, OF, and NETCONF are also being leveraged for Segment Routing-based MPLS networks. BGP-LS (still in the Internet Draft stage) can be used for topology discovery. In addition, certain network functions may require proprietary protocols. 

Most of south-bound protocol stacks are relatively new, for example Segment Routing this protocol is created to address the limitation of IP/MPLS technology.