Using DiffServ Markings to Prioritize Video Camera Traffic in PMP Networks

DiffServ Introduction

Cambium ePMP point-to-multipoint and point-to-point equipment enables operators to install video surveillance equipment in previously unconnected areas. In ePMP networks that serve both video surveillance traffic and other data traffic (i.e. web browsing), it is important to configure the ePMP network to give priority to the video and audio surveillance data.

To promote video and audio availability, the ePMP network may be set up to take advantage of the prioritizing benefits of Differentiated Services (or DiffServ) Quality of Service mechanisms. This architecture allows network operators to give low-latency prioritization to video traffic over the radio link. This article discusses how to configure an ePMP network to utilize DiffServ CodePoints (DSCP) to prioritize IP camera traffic and how this prioritization improves the way data is moved through the ePMP radio link.   This traffic prioritization is based on the 6-bit Differentiated Services field in the IP header present in the Ethernet frame header.

Configuring ePMP for DSCP Quality of Service

Once you have determined/configured the DSCP value markings utilized by the IP camera, you may begin to configure the ePMP network to handle the DSCP markings and prioritize the video traffic.

The ePMP platform supports three QoS priority levels (not available in ePTP Slave mode) using an air-fairness, priority-based starvation avoidance scheduling algorithm (Low (lowest), High, Voice (highest)). By default, with no other QoS priority assigned, traffic is sent with priority Low. Assuming that all other traffic is sent by default with priority Low, the procedure below uses DSCP marking configurations on the ePMP SM to prioritize the IP video camera traffic (through the ePMP radio uplink) as High (video) or Voice (audio), ensuring that the feed is serviced properly. The diagram below demonstrates the resulting traffic prioritization (assuming no other QoS implementations are active).

Use the following procedure to configure the ePMP SM to

  • Prioritize DSCP-marked packets (camera configured with audio DSCP 46) in the “Voice” priority queue for audio
  • Prioritize DSCP-marked packets (camera configured with video DSCP 34) in the “High” priority queue for video

SM DSCP Configuration – Audio (CodePoint 46)

  1. Access the ePMP SM web management interface and navigate to page Configuration > Quality of Service.
  2. In subsection Traffic Priority, configure parameter Traffic Priority to Enabled. This allows for the configuration of custom prioritization mechanisms.Screen Shot 2015-10-28 at 1.25.36 PM.png
  1. In Configuration > Quality of Service, set VoIP Screen Shot 2015-10-27 at 11.45.52 AM.pngPriority to Enabled. Two new rules are automatically added to the top of the QoS Classification Rules table, one for CoS 5 (Class of Service, not applicable in this case) and one for DSCP 46. By enabling VoIP Priority, you are ensuring that priority is given to audio and that the corresponding video data transfer does not consume available bandwidth. Also, audio traffic handling is optimized via the “Voice” priority mechanisms for better overall quality of delivery.
  1. Click the Save button to commit the changes.

SM DSCP Configuration – Video (CodePoint 34)

  1. In subsection Traffic Priority, add a new rule to the QoS Classification Rules table by clicking the Add button.
  1. In the new rule, set the Type to DSCP then configure the Details field to the DSCP marking configured in the IP Screen Shot 2015-10-27 at 11.48.29 AM.pngcamera settings. In this example, the camera is configured with a DSCP value of 34 for live video so the rule is set up with DSCP set to 34. Configure the Priority field to High to allow video traffic with DSCP markings of 34 and to take priority over all other non-prioritized network traffic traversing the SM uplink (assuming additional QoS configurations are not active, see section Other Considerations below). 
  1. Click the Save button to commit the changes.

Other Considerations

Implementing DSCP markings in a network may or may not be one of several QoS prioritization mechanisms present in a network’s access links and management network routing equipment. For example, an ePMP SM in the network with Subscriber Module Priority set to High may process all traffic at the same priority level as the DSCP marked video traffic discussed above (potentially nullifying the priority structure created with DSCP markings). This behavior may also be exhibited if additional QoS Classification Rules are created which utilize the same traffic priority configured for the Diffserv CodePoints. Ensure that the priority level of video traffic is set properly with respect to the other prioritization and queuing mechanisms in the network.