...
Each intermediate network device without traffic prioritization settings will increase the data transmission delay, and so the value of the delay amount is unpredictable. Thus, having a large number of intermediate devices without QoS policies implemented, will make the real-time services's operation impossible because of the mismatch with the quality indicators unattainability, i.e. traffic prioritization must be done performed along the entire network traffic transmission path (Figure 9b).
Keep in mind that implementing QoS policies is the only one component method to ensure the quality metrics. For a maximum effect, the QoS configuration should be synchronized with other settings. For example, using the TDMA technology instead of Polling on the InfiLINK 2x2 and InfiMAN 2x2 family families of devices reduces jitter by stabilizing the delay value (see TDMA and Polling: Application features).
| Center |
|---|
Figure 9a - Example of data distribution with partly implemented QoS policy
Figure 9b - Example of data distribution with implemented QoS policy |
...
The traffic prioritization mechanism
Traffic transmission path from From the management point of view in , the transmission path through the network can be described in two ways (Figure 10a, b):
- White-box: all the network devices in along the data propagation path are in the same responsibility zone. In this case, the QoS configuration on the devices can be synchronized, in accordance with according to the requirements described specified in the section above.
- Black-box: some network devices in the data propagation path are in a part of an external responsibility zone. The classification rules for incoming data and the algorithm for putting out packets from emptying the queues are configured individually on each device. The architecture of packets the packet queues implementation depends on the manufacturer of the equipment manufacturer, therefore there is no guarantee of the a correct QoS configuration on the devices in the external responsibility zone, and as a result, there is no guarantee of the high-quality performance indicators.
...
To solve the described problem for of the black-box network structure, labeling the packet headers can be performedlabeled: the priority required for during the packet processing is set in a header field and keeped is kept over the whole path. In this case, all intermediate devices can put the incoming data in the queue in accordance with the fields a queue according to the field values in which the priority is indicated. It will This require the development of standard protocols development and their the implementation of these protocols by the equipment manufacturers.
Keep in mind that usually, usually the equipment located in an external responsibility zone does not support data prioritization in accordance with the priority values in the service headers. Traffic priority coordination should be performed at the border of the responsibility zones border should be performed and at the administrative level, by implementing additional network configuration settings.
A The processing priority for of a packet can be set by using the service fields of various network protocols. This article describes the use of Ethernet and of the IPv4 protocol headers.
Priority within an Ethernet (802.1p)
...