SDN control of hybrid packet / optical leaf and spine network

9/19 DemoFriday: CALIENT, Cumulus Networks and InMon Demo SDN Optimization of Hybrid Packet / Optical Data Center Fabric demonstrated how network analytics can be used to optimize traffic flows across a network composed of bare metal packet switches running Cumulus Linux and Calient Optical Circuit switches.

The short video above shows how the Calient optical circuit switch (OCS) uses two grids of micro-mirrors to create optical paths. The optical switching technology has a number of interesting properties:

• Pure optical cut-through, the speed of the link is limited only by the top of rack transceiver speeds (i.e. scales to 100G, 400G and beyond without having to upgrade the OCS)
• Ultra low latency - less than 50ns
• Lower cost than an equivalent packet switch
• Ultra low power (50W vs. 6KW for comparable packet switch)

The challenge is integrating the OCS into a hybrid data center network design to leverage the strengths of both packet switching and optical switching technologies.

The diagram shows the hybrid network that was demonstrated. The top of rack switches are bare metal switches running Cumulus Linux. The spine layer consists of a Cumulus Linux bare metal switch and a Calient Technologies optical circuit switch. The bare metal switches implement hardware support for the sFlow measurement standard, and a stream of sFlow measurements is directed to an InMon's sFlow-RT real-time analytics engine, which detects and tracks large "Elephant" flows. The OCS controller combines the real-time traffic analytics with accurate topology information from Cumulus Networks' Prescriptive Topology Manager (PTM) and re-configures the packet and optical switches optimize the handling of the large flows - diverting them from the packet switch path (shown in green) to the optical circuit switch path (shown in blue).

The chart shows live data from the first use case demonstrated. A single traffic flow is established between servers. Initially the flow rate is small and the controller leaves it on the packet switch path. When the flow rate is increased, the increase is rapidly detected by the analytics software and the controller is notified. The controller then immediately sets up a dedicated optical circuit and diverts the flow to the newly created circuit.

The demonstration ties together a number of unique technologies from the participating companies:

• Calient Technologies
  • Optical Circuit Switch provides low cost, low latency bandwidth on demand
  • OCS controller configures optimal paths for Elephant flow
• Cumulus Networks
  • Cumulus Linux is the 1st true Linux Networking Operating System for low cost industry standard Open Networking switches
  • Prescriptive topology manager (PTM) provides accurate topology required for flow steering
  • Open Linux platform makes it easy to deploy visibility and control software to integrate the switches with the OCS controller.
• InMon Corp.
  • Leverage sFlow measurement capabilities of bare metal switches
  • sFlow-RT analytics engine detects Elephant flows in real-time

To find out more and see the rest of the demo, look out for the full presentation recording and Q&A when it is posted on SDN Central in a couple of weeks.

Update November 6, 2014: The recording is now available, Q&A + Video: SDN Helps Detect and Offload Elephant Flows in Hybrid Packet/Optical Fabric. 

Other related articles include:

• Helios: A Hybrid Electrical/Optical Switch Architecture for Modular Data Centers, describes early work in building hybrid networks that integrate packet and optical switches - original research paper describing advantages of hybrid architecture.
• RESTful control of Cumulus Linux ACLs - demonstrates how priority marking can be used to improve network latency. This complementary technology can be combined with optical circuit switching to further improve network performance.
• SDN fabric controller for commodity data center switches - overall architecture for building self tuning networks from commodity switches.

HP proposes hybrid OpenFlow discussion at Open Daylight design forum

Hewlett-Packard, an Open Daylight platinum member, is proposing a discussion of integrated hybrid OpenFlow at the upcoming Open Daylight Developer Design Forum, September 29 - 30, 2014, Santa Clara.

Topics for ODL Design Summit from HP contains the following proposal, making the case for integrated hybrid OpenFlow:

We would like to share our experiences with Customer SDN deployments that require OpenFlow hybrid mode. Why it matters, implementation considerations, and how to achieve better support for it in ODL

OpenFlow-compliant switches come in two types: OpenFlow-only, and OpenFlow-hybrid. OpenFlow-only switches support only OpenFlow operation, in those switches all packets are processed by the OpenFlow pipeline, and cannot be processed otherwise. OpenFlow-hybrid switches support both OpenFlow operation and normal Ethernet switching operation, i.e. traditional L2 Ethernet switching, VLAN isolation, L3 routing (IPv4 routing, IPv6 routing...), ACL and QoS processing

The rationale for supporting hybrid mode is twofold:

1. Controlled switches have decades of embedded traditional networking logic. The controller does not add value to a solution if it replicates traditional forwarding logic. One alternative controller responsibility is that provides forwarding decisions when it wants to override the traditional data-plane forwarding decision.
2. Controllers can be gradually incorporated into a traditional network. The common approach to enterprise SDN assumes a 100% pure SDN-controlled solution from the ground-up. This approach is expensive in terms of actual cost of new switches and in terms of downtime of the network. By providing a controller that can gradually migrate to an SDN solution, the hybrid approach enables customers to start seeing the value of having an SDN controller without requiring them to make a huge leap in replacing their existing network.

The Open Networking Foundation (ONF), the body behind the OpenFlow standard, released Outcomes of the Hybrid Working Group in March 2013, concluding:

On the whole, the group determined that industry can address many of the issues related to the hybrid switch. ONF does not plan or intend to incorporate details of legacy protocols in OpenFlow. The priority of ONF in this context is to explore the migration of networks to OpenFlow.

OpenDaylight has broad industry participation and should be a good forum to discuss integrated hybrid OpenFlow use cases, enhance open source controller support, and address multi-vendor interoperability. HP should find support for integrated hybrid OpenFlow among Open Daylight members:

• Brocade - Brocade has been shipping products supporting hybrid OpenFlow for over a year, see The Practical Path to SDN: Brocade OpenFlow Hybrid Port Mode. Brocade won the 2014 ONS SDN Idol competition with a solution for DDoS mitigation that combined their hybrid OpenFlow switches with the Open Daylight controller and InMon's real-time sFlow analytics software to address the challenge of mitigating large DDoS flood attacks - see ONS2014 SDN Idol finalist demonstrations
• Red Hat - Red Hat's Brent Salisbury is an OpenDaylight software developer and advocate for hybrid OpenFlow, see Hybrid OpenFlow Using The Normal Action
• Juniper - advocated for integrated hybrid OpenFlow at the 2012 ONF Summit, see Hybrid Programmable Forwarding Plane

SDN fabric controller for commodity data center switches discusses a number of use cases where an SDN controller can leverage the hardware capabilities of commodity switches through industry standard sFlow and hybrid OpenFlow protocols.

Integrated hybrid OpenFlow is a practical method for rapidly creating and deploying compelling SDN solutions at scale in production networks. It's encouraging to see HP engaging the Open Daylight community to deliver solutions based on hybrid OpenFlow - hopefully their proposal will find the broad support it deserves and accelerate market adoption of hybrid OpenFlow based SDN.

Update October 8, 2014: Slides from the summit are available, OpenFlow-hybrid Mode