The operation of MRM is based on communication and coordination between three types of network entities:
NOTE: The end-host implementations included in this directory adhere to the standard as much as possible. However, as the standard is still in flux, differences are likely to exist. Additionally, much of the testing with the end-host implementation has been done using MRM functionality implemented in Cisco IOS 12.0S.
Here you will see status reports displayed on your terminal.
Type Ctrl-C to exit the manager.
and MRM_Agents should be on different machines and there should be at most
one MRM_Agent running on a machine.
Note 2: Since the protocol uses port 679, both MRM_Manager and MRM_Agent should be super user level processes.
MRM_Manager: This is a very basic MRM manager tool running on an end-host. A user can use a configuration file to specify test parameters or can enter the values using the text based interface. If a configuration file is to be used, the name of the file should be supplied as command line argument to MRM_Manager ( see USAGE above ). Once the test parameters are specified, the manager sends requests to corresponding test senders and test receivers. The incoming Status Reports from test receivers are displayed on the terminal as they arrive. In order to stop the test and quit the MRM_Manager, the user presses Ctrl-C. The manager will then send test stop messages to test agents and quit.
The format of configuration file is important. Users should use the included ucsb-mrm-test-config1 configuration file as an example in creating test configurations. The parser reading this file is very sensitive.
For the test multicast addresses, a default value 0.0.0.0 causes the manager to select an address based on the manager's IP address. The exact address is determined by appending the last two octets of manager's IP address onto the end of 224.3. For example, if the manager is running on 126.96.36.199, the selected multicast address would be 188.8.131.52. We encourage users to use this default option, if suitable, to avoid multiple managers sending test requests with the same multicast address to the same end-host test agent. NOTE: the MRM_Manager must be run as ROOT.
MRM_Agent: This is the main MRM agent process running on an end-host. It listens to the UDP MRM port (679) and when it receives a Test Sender Request (TSR) or Test Receiver Request (TRR), it forks a new child and runs MRM_TS or MRM_TR. NOTE: the MRM_Agent must be run as ROOT.
MRM_TR: This code runs an MRM Test Receiver and
is initiated by the MRM Agent. It joins the multicast group and listens
for incoming data packets. The Test Receiver computes loss information
every second and sends Status Reports to the manager. Currently it uses
only unicast for Status Reports. Reports are only sent to the manager.
In calculating loss, it uses timer interrupts. After each second,
the Test Receiver generates an interrupt and examines the test packets
during the last window (one second). Because information is stored about the arrival of each MRM packet, loss information can be calculated in more detail than a standard RTP loss calculation. For example, in a given interval, if x test packets are lost and y are duplicated and x = y, RTP will calculate a 0% loss. The MRM Test Receiver will report that x packets are lost (and ignore the y duplicate packets). If x = 0 packets are lost, the MRM Test Receiver will report any duplicate packets, if y>0 (as negative loss). Ideally the MRM Test Receiver should report two numbers: lost and duplicate packets but only one field exists.
(***) : If you want
to have more than one test senders or test receivers, you should have a
separate line for each of them. For example, if you want to have 3 test
senders, then the config file should follow as:
Number of Test Senders : 3
Enter Sender IP : 184.108.40.206
Enter Sender IP : 220.127.116.11
Enter Sender IP : 18.104.22.168
(****) : This option is not implemented in the current Cisco implementation. They send test packets of size 16 bytes only.
- In the current Cisco implementation, Status Report ACK messages are improperly formatted. When the Cisco MRM Manager receives a Status Report ACK, it is discarded instead of processed. In order to avoid unnecessary retransmissions, Test Receivers will send Status Reports only once.
- The Test Sender supports RTP formatted test data ONLY.
- In the MRM Draft, TSR packets have a field specifying the IP address that the TS should use to source packets. This option allows routers to spoof IP packets. For security, this option is not allowed in the end-host implementation.
- Test Receiver uses ONLY unicast to send status reports to the manager.
- There is no way to specify a TTL value for test packets. Test Senders set a TTL of 127.
- The MRM Agent executes a new process to serve to each test session request. Once a test is started, the test parameters cannot be changed. The Manager must end the current test and start a new test.