Trellis is a unique combination of an underlay leaf-spine fabric, overlay virtual networking and unified SDN control over both underlay and overlay. The figures below show where Trellis fits in the CORD architecture.
Figure 1. Trellis Figure 2: CORD Architecture and Trellis
While the underlay and overlay are independently useful, and can be used independently, there are distinct advantages in having common SDN control over both overlay and underlay. The latter enables simple, efficient implementations of
- Distributed Virtual Routing for tenant networks
- Optimized delivery of multicast traffic streams
and many more optimizations & new capabilities to be introduced in the near future.
In the current implementation, there are actually two sets of ONOS controllers with different responsibilities. The first ONOS cluster (onos-cord) is responsible for the overlay infrastructure (virtual networking and service composition) and the access infrastructure. This cluster hosts the VTN and vOLT applications, respectively.
The second ONOS cluster (onos-fabric) is responsible for controlling the fabric and interfacing with conventional upstream routers. This cluster hosts the Fabric Control and vRouter applications, respectively.
Multicast control is via two additional applications, IGMP snooping and PIM-SSM, where the former runs on onos-cord and the latter runs on onos-fabric. (For simplicity, we show only a single Multicast Control application in Figure 2.)
In principle, all the applications could run on a single ONOS cluster. We chose to split responsibilities to have better isolation and separation of concerns, which was especially helpful during development. However, to simplify the exposition and diagrams, we show all the applications running on a single ONOS cluster in Figure 2.
For more information about each sub-system of the network infrastructure, see the following related pages: