Priority and end-to-end QoS

An important call meets a loaded network

Lea calls Niko in the FRMCS pilot. At the same time, a vehicle uploads measurement files. Both applications use transmission resources, but delayed speech disrupts the conversation while a file can often wait a little longer. “Voice first” is therefore an operational preference. The network needs rules for the respective data flows to turn it into specific behaviour.

Quality of Service (QoS) means controlled treatment of traffic in terms of properties such as delay, loss rate and available data rate. QoS is not a quality label for the entire connection. It describes mechanisms and agreed properties within defined boundaries.

Separate three decisions

The 5G system handles traffic in QoS Flows. A flow is a group of packets intended to receive the same QoS treatment. The application must therefore be mapped appropriately to transport treatment; the word “emergency” in a user interface does not itself change network resources.

The 5G QoS Identifier (5QI) refers to a flow's QoS characteristics. These include, for example, a priority level for packet treatment and provisions for delay and error rate. Standardised and dynamically assigned 5QIs must be distinguished; a number without an application profile is not a complete FRMCS concept.

Allocation and Retention Priority (ARP) instead controls admission and retention decisions for a flow when resources are scarce. ARP also includes whether a flow may pre-empt others or be pre-empted itself. It is therefore not the parameter that prioritises each individual speech packet in a queue. [S13]

A reserved rate is not a complete commitment

Guaranteed Bit Rate (GBR) denotes a QoS resource type with agreed guaranteed-bit-rate parameters. Non-GBR does not provide this type of guaranteed bit rate. Its flows receive the QoS treatment defined for them without that GBR commitment. Even GBR replaces neither radio coverage nor a complete view of application, service, network and terminal. Interruptions or an overloaded service server do not disappear because of the label.

Pre-emption means existing resource use can be restricted or ended in favour of use with greater entitlement. Whether and how this happens must be specified. Talbahn cannot simply infer that every ongoing communication should be interrupted.

A Network Slice is a logically separated network area with defined properties. It can help separate traffic and responsibilities. Shared radio sites, power supplies or computing resources may nevertheless remain common bottlenecks. A slice therefore does not demonstrate the quality of the group call either.

Turn the claim into a trial

For its case file, Talbahn requires a trial with simultaneous voice and measurement traffic. It defines load, measurement boundaries, expected treatment and failure conditions beforehand. Evidence must include the mapping between service priority and transport rules. A successful measurement without competing load does not answer the initial question.

Connect the service request to transport treatment

The application requests a communication purpose or category. The service side processes it under its profile and signals the required treatment. An appropriate transport policy then maps that requirement to permitted QoS resources. Policy means the rules used by the network to assign resources and treatment. There is consequently no universal equation “requested priority = 5QI”.

The ETSI service edition describes requested-priority signalling; the 5G system architecture explains transport mechanisms. Talbahn draws the handover between them and verifies the implemented mapping. [S09, clause 6.2.5; S13]

In the trial, voice competes with diagnostic traffic. Observations cover the application request, service classification, assigned transport treatment and outcome at both applications. This distinguishes incorrect configuration, rejected resource allocation and another bottleneck as possible explanations.

Check your understanding

A supplier shows a GBR flow and claims that this demonstrates the emergency call. What three additions do you require?

Model answer

First, I require the mapping of the service requirement to 5QI, ARP and pre-emption rules. Second, I need the boundaries considered and the treatment under resource scarcity. Third, I require an end-to-end test under defined load, including service, terminals and failure conditions. GBR alone does not demonstrate these points.

What to remember

Packet treatment, admission and actual service quality are different assessment subjects.

Your Talbahn case file

For the group call, add the mapping of service priority, QoS treatment and admission. Describe a load case and the result to observe.