International telecommunication union
Reference model of Connectivity
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- Layered model of performance
Reference model of ConnectivityVariations in connectivity configurations and diversity of use cases make development of a single universal figure for end-to-end IMT-2020 connectivity impossible. Since prospective IMT-2020 applications and legacy telecommunication services have to cover short-range communication and inter-continental communication, various connectivity configurations should be considered. For example, the longest connectivity will have length of 27,500km (half of the equatorial circumference of the Earth, ITU-T Recommendation G.801) while V2V (Vehicle-to-vehicle) communication can take place in the connectivity of less than10m. The following figure presents a general reference configuration for the connectivity of IMT-2020. The connectivity may be delivered via both wireless and wireline media. ……. Operator 2 Operator 1 Human-Machine Interface Network Interface Network Interface Connectivity between multi-operators User
User E-SP
E-SP Operator N - E-SP: End-Service Platform (i.e., Mobile/smart phone, data server, appliances, TV, etc.)
* Note: configurations #1 ~ #3 each consist of wireless-wireline, wireline-wireline, and wireless-wireless communications, but figure 5 shows only wireless-wireline communication for simplicity While the first three connectivity cases are already utilized by the legacy telecom service, IMT-2020 specific connectivity (i.e., case #4&5) may not fully supported by legacy connectivity and this calls for a new approach. Traditional SDOs (ITU, 3GPP, etc.) have already defined QoS requirements of the first three connectivity cases excellently and relatively minor modifications will be necessary for them to be applied to IMT-2020. However, IMT-2020 specific connectivity (such as case #4&5) is not covered by existing standards and a new QoS framework to address the case is necessary. 
Figure 5. Various configurations of connectivity The diversity of configurations suggests that high-level end-to-end QoE requirement for IMT-2020 needs to consider the distance and the complexity (i.e., number of telecommunication systems) of the configuration in concern. Therefore, the standard should define allocation rules based on longest reference case of connectivity and requirements for specific use cases based on shorter reference case of connectivity.
For operators to realize the customer QoE requirements in IMT-2020 network, QoS engineering is required for different network technologies and protocols. While this document focuses on the concept of connectivity, which is independent of underlying technologies/protocols, it is nevertheless necessary to consider their effects in different layers. As an example, the delay perceived by user may consist of delays from the processing in application layer, the transfer of packets in IP layer, the overhead of interworking different protocols in the data link layer, and the delays in traveling from one source to another via a physical medium. For example, a VoIP call may have total accumulated delay of 100ms that consists of the following delays: 40ms processing delay in user handset, 50ms delay due to routing and 10ms propagation delay over fibre optic links. Also, having different media/protocol in the same layer affects the performance. For example, the distance and the complexity of connectivity must be taken into account to define delay-related requirements. If end-to-end connectivity with delay of less than 10ms is necessary, the connectivity should be designed within 1,600km of fibre optic links (because fibre optic link will have a propagation delay of 6.25μs/km as defined in ITU-T Recommendation I.356). Then the processing and queueing delays in a network system (i.e., router, switch, etc.) should be considered. If a network system issues 2ms delay for internal processing and queueing and 3 network systems are required in the connectivity, the distance of the link must be reduced accordingly into 640 km. If servers for specific services are required in the connectivity, these factors should be taken into account as well. Furthermore, if wireless links are employed in this connectivity, the connectivity must be engineered to suit the protocols and the technologies of wireless links. In other words, realizing customer’s QoE requirements must be based on the structure of technologies and protocols in different layers. This is why understanding of different layers of networks is indispensable. The figure below describes the general layered model that could serve as a reference for IMT-2020. Detailed layered models for different use cases and scenarios are for further study. 
Figure 6. Layered model of performance for IP service in IMT-2020 * Examples of lower layers are, Wireline: MPLS, Ethernet, Optic Fibre, etc. Wireless: PDCP, RLC, Air interface, etc. Directory: ITU-T -> focusgroups focusgroups -> International Telecommunication Union focusgroups -> Innovation of ict in Developing Countries focusgroups -> International Telecommunication Union focusgroups -> Telecommunication focusgroups -> Focus Group on Smart Grid focusgroups -> Telecommunication focusgroups -> Telecommunication focusgroups -> Telecommunication focusgroups -> Innovation of ict in Developing Countries focusgroups -> Innovation of ict in Developing Countries Download 0.91 Mb. Share with your friends:
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