policing v shaping...

PfR (the pie in the sky)

http://www.netcraftsmen.net/component/content/article/68-network-infrastructure/669-understanding-performance-routing-pt-1.html

In a nutshell, PfR is an alternative way of routing packets. Ordinarily, we use routing protocols to determine the shortest loop-free path from source to destination -- that is, in fact, the primary goal of all routing protocols: to find the shortest (i.e., fewest number of router hops) loop-free path to the destination. Since many protocols use link bandwidth as the way to determine cost, most of the time the shortest path is also the highest bandwidth path to the destination.

Sometimes, the highest bandwidth path is not the best one. The highest bandwidth path can be experiencing congestion – perhaps it is overloaded. Or, the highest bandwidth path can be experiencing a fault that limits throughput or drops packets.

Instead of selecting the shortest path, PfR selects a path based on the performance of the path. PfR can measure parameters such as delay, throughput, loss and reachability, among others, to select the best performing path, and route packets accordingly. PfR can respond to transient events or ‘soft errors’, such as temporary congestion, and route traffic through an alternate path.

watching brian dennis on PfR, ine youtube video...

 http://www.youtube.com/watch?v=2h3nTKpXacY

merely watching it as an introduction, however i was struck by a couple of statements...  

the first of which equated multicast with anycast... if you noticed in the last post, according to rfc 4921, the two are fundamentally different...

as per the rfc, an anycast address is indistinguishable from a unicast but what sets the anycast apart is that it is assigned to more than one node...

a multicast is assigned to multiple nodes as well, but the difference ends there... 
a multicast is used for transmission to select groups, and uses all 1's at the beginning of the address, or f's...


the other comment had to do with policing/shaping...  they are very different ideas...  policing will drop traffic exceeding the max agreed rate; shaping queues the excess traffic for retransmission resulting in a smoothing out of traffic over time as opposed to simply dropping the oversubsciption...

see below for an excellent graphic and explanation...

http://www.cisco.com/en/US/tech/tk543/tk545/technologies_tech_note09186a00800a3a25.shtml

Policing Versus Shaping

The following diagram illustrates the key difference. Traffic policing propagates bursts. When the traffic rate reaches the configured maximum rate, excess traffic is dropped (or remarked). The result is an output rate that appears as a saw-tooth with crests and troughs. In contrast to policing, traffic shaping retains excess packets in a queue and then schedules the excess for later transmission over increments of time. The result of traffic shaping is a smoothed packet output rate.

Shaping implies the existence of a queue and of sufficient memory to buffer delayed packets, while policing does not. Queueing is an outbound concept; packets going out an interface get queued and can be shaped. Only policing can be applied to inbound traffic on an interface. Ensure that you have sufficient memory when enabling shaping. In addition, shaping requires a scheduling function for later transmission of any delayed packets. This scheduling function allows you to organize the shaping queue into different queues. Examples of scheduling functions are Class Based Weighted Fair Queuing (CBWFQ) and Low Latency Queuing (LLQ).