International telecommunication union
Gap Analysis of Standards on IMT-2020
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- Definition of “End-to-End” in different standards
- Layered Approach for QoS Management
- QoS Classification
Gap Analysis of Standards on IMT-2020As noted in the previous section, current IMT-2020 QoS-related studies and views differ and are usually limited to RAN (Radio Access Network). While the need for standardization of single common end-to-end QoS is evident, the existing standards must be carefully studied in advance to identify topics for in-depth study. In this context, this section aims to provide a gap analysis20 of representative QoS standards of 3GPP and ITU-T. Before proceeding to gap analysis, some major terms must be defined to avoid confusion. 3GPP simply defines a concept of bearer, a link between two end-points defined by a certain set of characteristics, to implement QoS. ITU-T, on the other hand, distinguishes NP (Network Performance) from QoS to translate user demands to network operational attributes. While QoS is defined to be “collective effect of service performances which determine the degree of satisfaction of a user of the service,” NP is defined independently of terminal performance and user actions to provide information for system development, network planning, and O&M (operation and maintenance). In other words, QoS views the “quality” of network in the user’s perspective and the other two (bearer and NP) views the same concept in network providers’ perspective. This document will follow the definitions as provided by 3GPP and ITU-T.
3GPP’s concept of “end-to-end” comprehensively covers the whole network from a user’s device to another user’s device. However, its UMTS bearer concept is limited to an interval starting from user’s device to PDN gateway (a gateway in wireless core network) for the sake of practicality (i.e., a network operator can influence only its network and its radio interface). (3GPP TS 23.107, TS 23.401 Rel.12) ITU-T, on the other hand, attempts to identify network QoS from end user to end user by defining UNI (User Network Interface) to UNI objectives in Y.1541. The concept, however, is usually applied to wireline IP-based services without any specific discretion on technologies of lower layers. 
Figure 1. The scope of 3GPP (Red) and ITU-T Standards (Purple)
The all-IP nature of IMT-2020 network allows data to be transported without connection on IP layer. With a given pair of source and destination IP address, IP packets are transferred from an end to another. The performance of an IP service, however, also depends on the performance of other layers (both upper and lower layers) and it is important to identify/acknowledge the relationship between performances of different layers. ITU-T’s Y.1540 standard provides a layered model of performance of IP service to illustrate the point aforementioned. The lower layers do not have end-to-end significance (i.e., it transfers packet from a point to another) but the type of technology employed (e.g., Ethernet-based leased lines) may affect the performance. Higher layers may also affect performance. 3GPP’s bearer acknowledges the effect of various layers on IP services, but defines the bearer on layer 1 and 2 for the use of higher layers (3GPP TS 23.107 & 23.401). Nevertheless, both acknowledge that the framework must take into account the impact from performance of layer 1 and 2 in both wireline and wireless media. Not only is the scope of the standards different, but also classification of QoS. 3GPP (TS 23.107, 23.203, 23.401) classifies QoS bearer using QCI (QoS class identifier) and ARP (Allocation and Retention Priority). QCIs provide the thresholds of basic parameters such as packet delay and packet error loss rate, while ARP provides the basis for establishing different bearers in the face of resource limitations (i.e., it prioritizes the allocation and retention of bearers not packets). The bearers are provided as either GBR (bearer with the minimum guaranteed bit rate per bearer) or MBR (the maximum guaranteed bit rate per EPS bearer). In other words, some applications (mission critical applications such as conversational voice and conversational video) are to be provided via GBR bearer and other applications are to be provided via MBR bearer. ITU-T, on the other hand, specifies six classes (one of whose parameters are unspecified) of QoS to differentiate and guarantee traffic quality. While the details of classification is different, 3GPP’s basic philosophy of differentiating mission-critical class traffic from default best-effort traffic is also inherent in ITU-T’s QoS classification.
Table 1. 3GPP’s QoS Classification (QCI only)
Table 2. ITU-T’s QoS Classification (QoS Class)
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