Monday, January 7, 2013

SDN and delay

Figure 1: Components of delay in a feedback control system
Delay and stability, describes the critical importance of low latency in building stable and effective feedback control systems. The article lists the different components of delay which are drawn in the timeline shown in Figure 1.

Feedback control describes how a system responds to changes, or disturbances. For example consider how you might respond to a denial of service attack. The first component of delay is the measurement delay: the time taken by the monitoring system to detect the attack and generate actionable information (for example the IP addresses of the attacker and victim). Next there is planning delay: the time taken to decide how to respond to the attack, for example weighing alternatives and deciding to null route traffic. Implementing the plan involves configuration delay as command line commands are input into the router. Next, there is a delay as the route propagates and finally the effect of the control is seen as the denial of service traffic is dropped by upstream routers.
Figure 2: Low latency software defined networking control loop
The software defined networking (SDN) control system, shown in Figure 2, significantly reduces the time taken execute the control loop. The sFlow standard provides multi-vendor, scaleable, low latency monitoring of the entire network, server and application infrastructure. The sFlow-RT real-time analytics engine detects the denial of service attack within seconds and provides actionable information to an SDN application which automates the planning process and immediately responds with commands to the Controller. The OpenFlow protocol provides a fast, programatic means for the controller to re-configuring forwarding in the network devices, significantly reducing the configuration delay.

Performance aware software defined networking solutions reduce response times from minutes to a seconds. The article, Delay and stability, describes why low latency is an essential pre-requisite to creating stable feedback control systems. The increased speed of response provided by sFlow and OpenFlow allows new classes of problem to be addressed, like dynamic load balancing, that significantly improve efficiency and performance by adapting the network to rapidly changing demands.

Network virtualization is one of the major applications for software defined networking. The article, Tunnels, describes how traffic in virtual network is tunneled over a shared physical network (and how standard sFlow monitoring is able to observe the tunneled traffic). While virtual networks are logically separate, they share the same physical infrastructure. Feedback control is essential to load balance traffic between virtual networks to ensure quality of service, reduce costs and increase scaleability by optimizing the use of the shared physical network assets.

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