Architectural Components

The only components of the network that require modification by NBP are edge routers. The input ports of egress routers must be modified to perform per-flow monitoring of bit rates, and the output ports of ingress routers must be modified to perform per-flow rate control. In addition, both the ingress and the egress routers must be modified to exchange and handle feedback.

Figure 3: An input port of an NBP egress router

Figure 3 illustrates the architecture of an NBP egress router's input port. Packets sent by ingress routers arrive at the input port of the egress router and are first classified by flow. In the case of IPv6, this is done by examining the packet header's flow label, whereas in the case of IPv4, it is done by examining the packet's source and destination addresses and port numbers. Each flow's bit rate is then rate monitored using a rate estimation algorithm such as the Time Sliding Window (TSW) [11]. These rates are collected by a feedback controller, which returns them in backward feedback packets to an ingress router whenever a forward feedback packet arrives from that ingress router. In some cases, to be described later in this section, backward feedback packets are also generated asynchronously; that is, an egress router sends them to an ingress router without first waiting for a forward feedback packet.

Figure 4: An output port of an NBP ingress router

The output ports of NBP ingress routers are also enhanced. Each contains a flow classifier, per-flow traffic shapers (e.g., leaky buckets), a feedback controller, and a rate controller. See Figure 4. The flow classifier classifies packets into flows, and the traffic shapers limit the rates at which packets from individual flows enter the network. The feedback controller receives backward feedback packets returning from egress routers and passes their contents to the rate controller. It also generates forward feedback packets, which it periodically transmits to the network's egress routers. The rate controller adjusts traffic shaper parameters according to a TCP-like rate control control algorithm, which is described later in this section.