Tech-invite  3GPPspace  IETFspace
◀  ▶  21  22  23  24  25  26  27  28  29  31  32  33  34  35  36  37  38  4‑5x

Content for  TR 26.925  Word version:  19.0.0

Top   Top   Up   Prev   Next
0…   4…   5…   6…   7…   8…   A… 
8 Applicability of existing 5Qis  8.1 QoS Model  8.1.1 Overview  8.1.2 5G QoS Parameters  8.1.3 5G QoS Characteristics  8.1.4 Standardized 5QI to QoS characteristics mapping  8.1.5 Considerations for Media Services 

 

8  Applicability of existing 5Qis  p. 28

8.1  QoS Model  p. 28

8.1.1  Overview  p. 28

Clause 5.7 of TS 23.501 explains the QoS Model for 5G. The 5G QoS model is based on QoS Flows. The 5G QoS model supports both QoS Flows that require guaranteed flow bit rate (GBR QoS Flows) and QoS Flows that do not require guaranteed flow bit rate (Non-GBR QoS Flows). The 5G QoS model also supports Reflective QoS (see clause 5.7.5 of TS 23.501).
A QoS Flow ID (QFI) is used to identify a QoS Flow in the 5G System. User Plane traffic assigned to the same QoS Flow within a PDU Session receives the same traffic forwarding treatment (e.g. scheduling, admission threshold).
The QFI may be dynamically assigned or may be equal to the 5QI, for more details on existing 5QI see clause 8.1.2.
A QoS Flow may either be 'GBR', 'Non-GBR' or "Delay Tolerant GBR" depending on its QoS profile and it contains QoS parameters as follows:
  • For each QoS Flow, the QoS profile includes the QoS parameters:
    • 5G QoS Identifier (5QI); and
    • Allocation and Retention Priority (ARP).
  • For each Non-GBR QoS Flow only, the QoS profile can also include the QoS parameter:
    • Reflective QoS Attribute (RQA).
  • For each GBR QoS Flow only, the QoS profile also include the QoS parameters:
    • Guaranteed Flow Bit Rate (GFBR) - UL and DL; and
    • Maximum Flow Bit Rate (MFBR) - UL and DL; and
  • In the case of a GBR QoS Flow only, the QoS profile can also include one or more of the QoS parameters:
    • Notification control;
    • Maximum Packet Loss Rate - UL and DL
The usage of a dynamically assigned 5QI for a QoS Flow requires in addition the signalling of the complete 5G QoS characteristics (described in clause 5.7.3 of TS 23.501) as part of the QoS profile.
The principle for classification and marking of User Plane traffic and mapping of QoS Flows to Access Network (AN) resources is illustrated in Figure 8-1-1.
Copy of original 3GPP image for 3GPP TS 26.925, Fig. 8-1-1: The principle for classification and User Plane marking for QoS Flows and mapping to AN Resources
Figure 8-1-1: The principle for classification and User Plane marking for QoS Flows and mapping to AN Resources
(⇒ copy of original 3GPP image)
Up

8.1.2  5G QoS Parameters  p. 29

A 5QI is a scalar that is used as a reference to 5G QoS characteristics defined in clause 5.7.4 of TS 23.501, i.e. access node-specific parameters that control QoS forwarding treatment for the QoS Flow (e.g. scheduling weights, admission thresholds, queue management thresholds, link layer protocol configuration, etc.).
Standardized 5QI values have one-to-one mapping to a standardized combination of 5G QoS characteristics as specified in Table 5.7.4-1 of TS 23.501 and shown below in Table 8.1.4-1.
A summary of the most relevant QoS Parameters is provided as follows. For details, please refer to clause 5.7.2 of TS 23.501:
  • Guaranteed Flow Bit Rate (GFBR) - UL and DL, for GBR QoS Flows only: denotes the bit rate that is guaranteed to be provided by the network to the QoS Flow over the Averaging Time Window.
  • Maximum Flow Bit Rate (MFBR) -- UL and DL, for GBR QoS Flows only limits the bit rate to the highest bit rate that is expected by the QoS Flow (e.g. excess traffic may get discarded or delayed by a rate shaping or policing function).
  • The Maximum Packet Loss Rate (UL, DL) indicates the maximum rate for lost packets of the QoS flow that can be tolerated in the uplink and downlink direction, if the flow is compliant to the GFBR and is only used for voice media traffic in rel.16.
Up

8.1.3  5G QoS Characteristics  p. 29

In addition to 5G QoS parameters, also 5G QoS characteristics are defined in TS 23.501. The characteristics describe the packet forwarding treatment that a QoS Flow receives edge-to-edge between the UE and the UPF in terms of the following performance characteristics:
  1. Resource Type (GBR, Delay critical GBR or Non-GBR): determines if dedicated network resources related to a QoS Flow-level Guaranteed Flow Bit Rate (GFBR) value are permanently allocated (e.g. by an admission control function in a radio base station).
  2. Priority level; indicates a priority in scheduling resources among QoS Flows.
  3. Packet Delay Budget; defines an upper bound for the time that a packet may be delayed between the UE and the UPF that terminates the N6 interface. In uncongested scenarios, 98 percent of the packets are expected to be within the packet delay budget.
  4. Packet Error Rate: The Packet Error Rate (PER) defines an upper bound for the rate of PDUs (e.g. IP packets) that have been processed by the sender of a link layer protocol (e.g. RLC in RAN of a 3GPP access) but that are not successfully delivered by the corresponding receiver to the upper layer (e.g. PDCP in RAN of a 3GPP access).
  5. Averaging window (for GBR and Delay-critical GBR resource type only); The Averaging window represents the duration over which the GFBR and MFBR are calculated.
  6. Maximum Data Burst Volume (for Delay-critical GBR resource type only): denotes the largest amount of data that the 5G-AN is required to serve within a period of 5G-AN PDB.
Standardized or pre-configured 5G QoS characteristics, are indicated through the 5QI value. Signalled 5G QoS characteristics are provided as part of the QoS profile and include all of the characteristics listed above.
Up

8.1.4  Standardized 5QI to QoS characteristics mapping  p. 30

The one-to-one mapping of standardized 5QI values to 5G QoS characteristics is specified in Table 5.7.4-1 if TS 23.501 and shown below in Table 8.1.4-1.
5QI Value Resource Type Default Priority Level Packet Delay Budget Packet Error Rate Default Maximum Data Burst Volume (NOTE 2) Default Averaging Window Example Services
1GBR
(NOTE 1)		20100 ms10-2N/A2000 msConversational Voice
240150 ms10-3N/A2000 msConversational Video (Live Streaming)
33050 ms10-3N/A2000 msReal Time Gaming, V2X messages Electricity distribution - medium voltage, Process automation - monitoring
450300 ms10-6N/A2000 msNon-Conversational Video (Buffered Streaming)
65775 ms10-2N/A2000 msMission Critical user plane Push To Talk voice (e.g., MCPTT)
6620100 ms10-2N/A2000 msNon-Mission-Critical user plane Push To Talk voice
6715100 ms10-3N/A2000 msMission Critical Video user plane
752550 ms10-2N/A2000 msV2X messages
5Non-GBR
(NOTE 1)		10100 ms10-6N/AN/AIMS Signalling
660300 ms10-6N/AN/AVideo (Buffered Streaming) TCP-based (e.g., www, e-mail, chat, ftp, p2p file sharing, progressive video, etc.)
770100 ms10-3N/AN/AVoice, Video (Live Streaming)
Interactive Gaming
880300 ms10-6N/AN/AVideo (Buffered Streaming)
TCP-based (e.g., www, e-mail, chat, ftp, p2p file sharing, progressive video, etc.)
990
69560 ms10-6N/AN/AMission Critical delay sensitive signalling (e.g., MC-PTT signalling)
7055200 ms10-6N/AN/AMission Critical Data (e.g. example services are the same as QCI 6/8/9)
796550 ms10-2N/AN/AV2X messages
806810 ms10-6N/AN/ALow Latency eMBB applications Augmented Reality
82Delay Critical GBR1910 ms
(NOTE 4)		10-4255 bytes2000 msDiscrete Automation (see TS 22.261)
832210 ms
(NOTE 4)		10-41358 bytes
(NOTE 3)		2000 msDiscrete Automation (see TS 22.261)
842430 ms
(NOTE 6)		10-51354 bytes2000 msIntelligent transport systems (see TS 22.261)
85215 ms
(NOTE 5)		10-5255 bytes2000 msElectricity Distribution- high voltage (see TS 22.261)
NOTE 1:
A packet which is delayed more than PDB is not counted as lost, thus not included in the PER.
NOTE 2:
It is required that default MDBV is supported by a PLMN supporting the related 5QIs.
NOTE 3:
This MDBV value is set to 1354 bytes to avoid IP fragmentation for the IPv6 based, IPSec protected GTP tunnel to the 5G-AN node (the value is calculated as in Annex C of TS 23.060 and further reduced by 4 bytes to allow for the usage of a GTP-U extension header).
NOTE 4:
A delay of 1 ms for the delay between a UPF terminating N6 and a 5G-AN should be subtracted from a given PDB to derive the packet delay budget that applies to the radio interface.
NOTE 5:
A delay of 2 ms for the delay between a UPF terminating N6 and a 5G-AN should be subtracted from a given PDB to derive the packet delay budget that applies to the radio interface.
NOTE 6:
A delay of 5 ms for the delay between a UPF terminating N6 and a 5G-AN should be subtracted from a given PDB to derive the packet delay budget that applies to the radio interface.
Up

8.1.5  Considerations for Media Services  p. 33

8.1.5.1  General  p. 33

For media traffic considered in the present document, it is appropriate to understand, how they map to QoS parameters and characteristics, including the mapping to the 5QIs as indicated above.

8.1.5.2  Expected TCP/IP Performance for non-GBR  p. 33

Maximum achievable throughput for a single TCP connection is determined by different factors. One trivial limitation is the maximum bandwidth of the slowest link in the path. But there are also other, less obvious limits for TCP throughput. Packet loss can create a limitation for the connection as well as can the roundtrip time of acknowledgements.
The TCP Receive Window is the amount of data that a receiver can accept without acknowledging the sender. If the sender has not received acknowledgement for the first packet it sent, it will stop and wait and if this wait exceeds a certain limit, it may even retransmit. This is how TCP achieves reliable data transmission. Even if there is no packet loss in the network, this windowing limits throughput. Because TCP transmits data up to the window size before waiting for the acknowledgements, the full bandwidth of the network may not always get used. At any given time, the window advertised by the receive side of TCP corresponds to the amount of free receive memory it has allocated for this connection.
When packet loss occurs in the network, an additional limit is imposed on the connection. In the case of light to moderate packet loss when the TCP rate is limited by the congestion avoidance algorithm.
The Mathis equation is a formula that approximates the actual impact of loss on the maximum throughput rate:
Max Rate in bps < (MSS/RTT)*(1 / √p)
where
MSS = maximum segment size in bytes
RTT = round trip time in seconds
p = the probability of packet loss
While this equation obviously has limits in the details, it provides an excellent estimate on the estimated TCP throughput. Figure 8.1.5-1 shows the estimated TCP Throughput over One Way Latency for different packet loss rates and MSS 1500 bytes based on this equation, assuming that the RTT is twice the one way latency.
Copy of original 3GPP image for 3GPP TS 26.925, Fig. 8.1.5-1: Estimated TCP Throughput over One Way Latency for different packet loss rates and MSS 1500 bytes
Figure 8.1.5-1: Estimated TCP Throughput over One Way Latency for different packet loss rates and MSS 1500 bytes
(⇒ copy of original 3GPP image)
Up
Based on this equation, the estimated TCP throughput for some relevant streaming related Non-GBR 5QIs as documented in Table 8.1.4-1 are as follows:
  • 5QI = 7 with Latency=100ms and Packet loss rate 10e-3 results in estimated TCP Throughput of 237 kbit/s
  • 5QI = 8 and 9 with Latency=300ms and Packet loss rate 10e-6 results in estimated TCP Throughput of 2.5 Mbit/s
  • 5QI = 7 with Latency=10ms and Packet loss rate 10e-6 results in estimated TCP Throughput of 75 Mbit/s
The equation shows that typically TCP based streaming traffic is more susceptible to loss rates than to delay. It is also important that packet loss rates and latencies are not guaranteed and may therefore result in lower or higher throughput, for example in case of congestion or cell handoff. Hence, media services using these 5QI assignments preferably apply protocols that enable to adapt to these bitrates and changes.
Up

8.1.5.3  Bitrate considerations for GBR services  p. 34

If the service would be able to benefit from GBR QoS, then the GFBR and MFBR are relevant. A suitable characterization for a media service is the required minimum bitrate that it needs in order to maintain a good service quality. At the same time, a service is well characterized up to which bitrate it would still provide noticeable quality improvements. Such information may be static or may even change over time, depending on the complexity of the service.

8.1.5.4  Relevant Parameters for Media Services  p. 34

Based on this discussion, it is proposed that for Media services that use TCP-based distribution systems and permit rate adaptation (such as adaptive streaming services), the following information is worthwhile to be provided:
  • The typical bitrate at which the service preferable operates, possibly providing a range of the bitrate. It should also be mentioned if such information is static over the service or would change, and if such information may be configurable.
  • If there exists a minimum bitrate that the service should not fall below to maintain a sufficient quality. If this exists, a range would be preferable. It should also be mentioned if such information is static over the service or would change, and if such information may be configurable.
  • If there exists a maximum bitrate that the service beyond which the services does not created additional quality. If this exists, a range would be preferable. It should also be mentioned if such information is static over the service or would change, and if such information may be configurable.
Up

Up   Top   ToC