4.2 Example 2: Measuring Network Capacity

The following figure shows the layout of an example network that interconnects a media server and a TV with an integrated media player.

Example media server and TV, integrated media player network

Figure 7: Example media server and TV, integrated media player network

The media server is used to stream media content to the TV. The QoS support in this protocol can be used to assess the capacity of the connection between the two endpoints to determine if adequate bandwidth is available for a requested stream. This example describes the QoS exchange associated with this protocol for testing the bandwidth using a Test Type of Timed probes.

The following figure shows the protocol exchange between the media server and the TV. Communication between the controller and the sink is done using their real MAC addresses (no LLTD OUI–based MAC addresses) and the LLTD Ethertype.

Protocol exchange between media server and TV

Figure 8: Protocol exchange between media server and TV

The following list describes each step in the protocol exchange:

  1. The controller sends a QosInitializeSink header to the sink and indicates that the sink has to use its existing interrupt moderation setting (Interrupt Mod is set to 0xFF).

  2. The sink returns a QosReady header to confirm the creation of a network test session. The sink indicates that the Sink Link Speed is 54 Mbps (value of 540,000 or 0x83D60) and that its time-stamp counter has an accuracy of 1 microsecond (value 1,000,000 or 0xF4240).

  3. The controller creates its first QosProbe frame, time stamps it, and then transmits it to the sink. The controller indicates in the QosProbe frame that the Test Type is a Timed probe. The 802.1p field is indicated as not used. The sink time stamps this frame when it arrives and saves it for returning the header information to the controller when the controller requests it.

  4. The controller immediately creates a second QosProbe frame, time stamps it, and transmits it to the sink using the same parameters as in step 3. The sink time stamps this frame when it arrives and saves it for returning the header information to the controller when the controller requests it.

  5. The controller immediately creates a third QosProbe frame, time stamps it, and transmits it to the sink using the same parameters as in step 3. The sink time stamps this frame when it arrives and saves it for returning the header information to the controller when the controller requests it.

  6. The controller sends a QosQuery to the sink to retrieve the header information from the QosProbe frames.

  7. The sink sends a QosQueryResp to the controller and indicates that it has received three events. The QosProbe headers with both the controller and sink time stamps are included in the frame.

  8. The controller sends a QosReset to the sink to indicate that it is done running QoS tests.

  9. The sink confirms reception of the QosReset header with a QosAck header.