Quality of Service (QoS) – Application Marking Recommendations

In our hyper-connected world, prioritizing specific types of data traffic has become essential. Quality of Service (QoS) is a mechanism that enables us to efficiently manage data traffic by classifying and prioritizing different types of network traffic. In this post, we dive into the application marking recommendations for QoS and understand the importance of implementing QoS for Voice and Video applications.

Decoding QoS Application Marking

QoS application marking plays a crucial role in traffic classification. Different types of traffic, such as IP routing, voice, video, and data, have distinct requirements for speed, latency, and reliability. These requirements are met through specific classification values at Layer 2 (CoS, MPLS EXP) and Layer 3 (IPP PHB DSCP). Let’s look at the recommended marking for different types of traffic:

IP Routing 6 CS6 48 6 6
Voice 5 EF 46 5 5
Interactive Video 4 AF41 34 4 4
Streaming Video 4 CS4 32 4 4
Mission Critical 3 Cs3 24 3 3
Call Signals 3 AF31/CS3 26/24 3 3
Transactional Data 2 AF21 18 2 2
Network Management 2 CS2 16 2 2
Bulk Data 1 AF11 10 1 1
Scavenger 1 CS1 8 1 1
Best Effort 0 BE 0 0 0

Quality of Service for Voice Applications

Voice traffic is highly sensitive to performance indicators such as packet loss, latency, and jitter. Here’s how to handle Voice QoS:

  • Voice traffic should be marked to DSCP EF as per the QoS Baseline and RFC 3246.
  • Target performance standards include no more than 1% loss, one-way latency (mouth-to-ear) no more than 150 ms, and average one-way jitter less than 30 ms.
  • A guaranteed priority bandwidth between 21-320 kbps per call is required, depending on factors like the sampling rate, VoIP codec, and Layer 2 media overhead.
  • All three QoS quality factors: loss, latency, and jitter, directly affect voice quality and hence must be controlled judiciously.

Quality of Service for Video Applications

The QoS requirements for video traffic diverge based on whether the traffic is interactive or streaming. 

Interactive Video

Interactive video, such as IP video conferencing, requires specific QoS measures:

  • Interactive video traffic should be marked to DSCP AF41. Excess traffic can be marked down by a policer to AF42 or AF43.
  • As with voice traffic, target performance metrics include no more than 1% loss, one-way latency no more than 150 ms, and jitter not exceeding 30 ms.
  • It’s recommended to overprovision interactive video queues by 20% to accommodate bursts.

Streaming Video

For streaming video, traffic should be marked to DSCP CS4. More specific recommendations vary based on individual network characteristics and will be the subject of future discussions.

In conclusion, implementing Quality of Service is vital for efficient data traffic management, particularly for voice and video applications, which are highly sensitive to latency, jitter, and loss. The above recommendations provide a starting point for determining how to classify and mark different types of traffic on your network.