BWCTL Architecture

$Date: 2004/09/14 22:55:52 $

In the general case, BWCTL works by having a bwctld process on each of the endpoint test systems. The bwctl client contacts each of those daemons and requests a test. That request includes an indication of the desired time period as well as a full parameterization of the desired Iperf test. bwctld is responsible for implementing the policy and scheduling constraints.

General Case

bwctld has been developed as a classic accept/fork daemon. The master daemon process listens for new network connections and also manages the resources for all child bwctld processes. Once a connection comes in, bwctld forks a child process to handle that request. The child process deals with all encryption and communication issues with the client, as well as dealing with all static resource limits. Static resource limits are those not dependent upon what is currently happening on the node. For example, the request broker can easily determine if the given client is allowed to do UDP tests without talking to the master daemon. Once the request broker process determines the request is valid, it makes a request to the master daemon for the resources and time period requested by the client. If the master daemon has the resources available (including the open time period), it grants the request.

The time period for the test is always requested by the client. It makes a request to the request broker process on each endpoint of the test in turn. The time period is requested by specifying two timestamps. The earliest time and the latest time the client is willing to settle for. The request broker either returns a tentative reservation with the first open time that will fulfill the parameters of the test or a request denied message. The client can then use the tentative reservation time as the earliest time in the request to the request broker on the other host. Eventually, an agreed upon time will be reached or the latest time will be reached. If the request broker can not fulfill the request before the latest time specified in the request, it will return a server too busy message. If the client gets the same time from both servers, it must then confirm the reservation with a start session message. The start session message must be received before a configurable timeout period and before the reservation time, or the server will disallow the reservation.

Once the client sends the the start session message, the request broker forks off a peer agent that is responsible for verifying the time offset to the other endpoint of the test and initializing the communication socket that will be used to trade results of the test.

If the test endpoint systems have a reasonably close idea of the time, and they can communicate, the peer agent forks off the test process. The test process waits until the scheduled start time and then executes Iperf with the correct command-line parameters. Note: Experience is showing that a closer integration with the testing process (Iperf) may be needed in the future.

In the event that the local host is one of the endpoints and there is no local bwctld running, bwctl will spawn additional processes to execute the local side of the test directly. In this case, a diagram of the processes involved would look like the following:

Local bwctld not available

The same basic communication takes place between the different processes in this alignment. The main difference is that the client has no need of a resource broker. This is the expected usage scenario for end user workstations to run tests to well defined BWCTL measurement beacons.

* The images above shows a dashed blue line around the processes that occur on each host.

$Id: architecture.html,v 1.7 2004/09/14 22:55:52 boote Exp $


Bandwidth Test Controller (BWCTL)	16 February, 2004
This material is based, in part, on work supported by the National Science Foundation (NSF) under Grant No. ANI-0314723. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NSF.