IPMP

1. The main reason IPMP is need to answer the question: "Where are the network delays occurring?" Currently this is hard to do because:
   1. routers often make bad measurement targets because they protect themselves against DOS attacks by processing ICMP at a low priority.
   2. there are often large variations in delay between successive packets following the same route.
   3. the delays on the reverse path are likely to be different to those on the forward path
   4. the path may change during a measurement
   ISPs are often compared unfairly because large parts of the delay are outside their control. Internet surveys take too little account of the service actually provided by the ISPs they measure. Partly this is because it is difficult. An ISP that wants to be able to discover and demonstrate the degree of delay introduced by it's network can deploy IPMP path record enabled routers at the boundaries of it's network.

2. To provide router support for one-way delay measurements.

3. To support measurement of protocol based priority queueing

IPMP also:

1. Supports forward and reverse path measurements of a single packet.

2. Supports BER measurements.

3. allows accurate RTT measurements

4. reduces the measurement overhead on the network.

IPMP does not require a router to maintain a real-time synchronized clock. Instead router that provide time stamp support can include whatever time stamp they have available at the interface in an IPMP packet.

The relationship to real time (if there is one) is established through a separate packet exchange in which the router includes time stamps and the real time that they relate to. These can then be used at the measurement station to convert the time stamps received to real time.

This approach is intended to make life easier for the router and increase the implementation options at the router, thereby improving the accuracy of the final time stamp.

A typical implementation might be a free running clock (of known precision and maximum drift against real time) and a GPS providing 1s time signals to the router through a serial port. The main CPU on the router receives notification the GPS time signal via an interrupt and records the GPS time and the value of all interface clocks. This data, along with maximum measurement error information is sent to measurement hosts, on request, via the IPMP Information Request Packet.