Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
ISO/IEC 29341-8-11: UPnP Quality of Service — QoS Traffic Classes
Understanding the standardized traffic classification scheme for UPnP QoS — TC_AD, TC_AV, TC_BE, TC_BK and beyond
ISO/IEC 29341-8-11 defines the QoS Traffic Classes component of the UPnP QoS architecture, establishing a standardized classification scheme that maps network application traffic into distinct service categories. Each traffic class is associated with a specific priority level, queuing treatment, and forwarding behavior. The traffic class taxonomy defined in this standard ensures consistent QoS treatment across heterogeneous UPnP devices from different vendors, enabling true interoperability in multi-vendor QoS deployments. Without a standardized classification scheme, each device might interpret priorities differently, defeating the purpose of end-to-end QoS.
Map application traffic to the most specific traffic class available for optimal resource allocation. Using overly broad classes (such as classifying all traffic as best-effort) negates the benefits of the QoS architecture.
Traffic Class Taxonomy and Priority Model
The QoS Traffic Classes specification defines a hierarchical classification system with multiple service classes, each designed for a specific category of network application. The primary traffic classes include TC_AD (Audio/Data — highest priority, reserved for real-time interactive audio such as VoIP), TC_AV (Audio/Video Streaming — for one-way or streaming media), TC_BE (Best Effort — standard data traffic), and TC_BK (Background — low-priority bulk transfers). Each class is assigned a recommended per-hop behavior (PHB) code point for DSCP marking and an IEEE 802.1p priority value, ensuring consistent Layer 2 and Layer 3 treatment.
The priority model uses an 8-level hierarchy aligned with the IEEE 802.1p priority levels (0-7). Traffic class 7 is reserved for network control traffic (such as routing protocols), class 6 for voice, class 5 for video, classes 4-3 for controlled load and excellent effort, class 2 for best effort, and classes 1-0 for background and less-than-best-effort traffic. The specification allows vendors to define additional sub-classes within this framework while maintaining interoperability at the primary class level. Applications request a specific traffic class through the QoS Manager, which then maps this request to the appropriate device-level configuration.
| Traffic Class | Priority Level | DSCP Mapping | 802.1p Value | Example Applications |
|---|---|---|---|---|
| TC_AD | 7 (Highest) | EF (46) | 6 | VoIP, Video Conferencing, Real-time Control |
| TC_AV | 5 | AF41 (34) | 5 | IPTV, Streaming Media, Distance Learning |
| TC_BE | 3 | DF (0) | 2 | Web Browsing, Email, API Traffic |
| TC_BK | 1 | CS1 (8) | 1 | File Downloads, Backup, Software Updates |
Using too many distinct traffic classes increases management complexity without proportional QoS benefit. For most enterprise and home networks, 4 to 6 traffic classes provide optimal balance between granularity and administrability.
Mapping Application Requirements to Traffic Classes
Properly mapping applications to traffic classes is one of the most important engineering tasks in QoS deployment. Each application has unique network requirements in terms of bandwidth, latency, jitter, and loss tolerance. Voice traffic requires low latency (under 150 ms one-way) and minimal jitter (under 30 ms), but is relatively tolerant of packet loss (up to 1%). Video streaming is sensitive to both jitter and loss but can tolerate higher latency. Bulk data transfers are latency-tolerant but throughput-sensitive. The traffic class framework in ISO/IEC 29341-8-11 provides guidance for mapping these diverse requirements to the appropriate service class.
A practical engineering approach is to perform an application profiling exercise before implementing QoS: measure each application’s bandwidth consumption, identify its latency and jitter sensitivity, determine its business criticality, and then map it to the appropriate traffic class. The profiling results should be documented and reviewed periodically as application behavior evolves. The QoS Traffic Classes specification supports this through the TrafficClassProfile state variable, which allows devices to report the specific characteristics and recommended uses of each supported traffic class.
A well-designed traffic class mapping ensures that voice, video, and data applications can coexist on the same network without mutual degradation, even under heavy load conditions.
Without proper traffic classification, all packets are treated equally during congestion, causing real-time applications like VoIP and video conferencing to suffer packet loss and delay that render them unusable.
Frequently Asked Questions
Q: Can I create custom traffic classes beyond the standard four?
A: Yes, the specification allows vendors to define additional sub-classes while maintaining interoperability at the primary class level. Custom classes must be mapped to one of the standard DSCP or 802.1p priority values to ensure consistent behavior across multi-vendor networks.
A: Yes, the specification allows vendors to define additional sub-classes while maintaining interoperability at the primary class level. Custom classes must be mapped to one of the standard DSCP or 802.1p priority values to ensure consistent behavior across multi-vendor networks.
Q: How does the traffic class mapping interact with DiffServ domains?
A: The traffic classes defined in this standard are designed to align with DiffServ PHB groups. TC_AD maps to Expedited Forwarding (EF), TC_AV to Assured Forwarding (AF41), TC_BE to Default Forwarding (DF), and TC_BK to Class Selector 1 (CS1). This alignment ensures consistent QoS marking across administrative domain boundaries.
A: The traffic classes defined in this standard are designed to align with DiffServ PHB groups. TC_AD maps to Expedited Forwarding (EF), TC_AV to Assured Forwarding (AF41), TC_BE to Default Forwarding (DF), and TC_BK to Class Selector 1 (CS1). This alignment ensures consistent QoS marking across administrative domain boundaries.
Q: What happens if a device does not support a requested traffic class?
A: The QoS Manager queries each device’s
A: The QoS Manager queries each device’s
QosDeviceCapabilities to determine which traffic classes are supported. If a requested class is not available, the manager can negotiate a downgrade to the nearest available class and notify the application of the modified treatment.Q: Is there a mechanism for applications to discover available traffic classes?
A: Yes. The QoS Manager exposes the
A: Yes. The QoS Manager exposes the
GetSupportedTrafficClasses action, which returns a list of traffic classes available on the network along with their characteristics, enabling applications to make informed QoS requests.
