Bi-Directional Multicast UDP Test Utility (BiDir MPing)

In a previous post (last month) I introduced the System Monitoring Framework that my old team developed and used for monitoring our complex systems environment. One of the systems that we looked after used bi-directional multicast UDP (User Datagram Protocol) - which allowed the system to communicate in a "battle-net" like topology.

Multicast UDP is a great routing protocol and in my opinion is under-utilised by many developers. It is often used in live video streaming where instead of sending a packet of data to each of n clients (i.e. n packets) a single packet is sent to a multicast address which is then distributed at the last possible routing node to the individual clients (therefore limiting the total number of packets routed across the network). See Wikipedia for more info.

Most applications of multicasting (sometimes referred to as multiplexed broadcast) only require packets to be routed from one node to many other nodes (i.e. a 1 to many relationship as in the video streaming example above). In our case however the system used bi-directional multicasting (i.e. a many to many relationship - hence the "battle net" analogy).

Fig 1: Normal UDP. 1 packet is sent to 3 clients resulting in 6 packet sends in total.

Fig 2: Multicast UDP. 1 packet is sent to 3 clients resulting in 4 packet sends in total.

Fig 3: Bi Directional Multicast UDP: Example shows all nodes particpating via the multicast address at the router.

If you want to test multicast UDP there are a number of "ping"-like command utilities available such as mping from Microsoft Research. These however do not test bi-directionality and so, yet again I built my own test utility. To my knowledge this is the ONLY utility available that will directly test bi-directionality of multicast UDP.

The test utility uses a controller which instructs nodes participating in the test to "ping" each other via the multicast address, listen for pings from other nodes and then report back. The results are compiled and analysed by the controller and displayed on screen and/or written to a database for historical reporting.

With the complex network routings we had in our particular system we often found that the programmed settings of routers would change as the network guys fiddled things around or secondary routers took over from primary paths. This meant that we occasionally saw the multicast routes fail to allow bi-directionality and hence the need for the test utility and the ability to report out to a database. The database reporting capability meant that we could also display the results in our System Monitoring framework (see previous post)

Here's the documentation for the utility in case anyone is interested.