International telecommunication union
Network softwarization in 5G mobile networks
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- 6.6.2 Horizontal extension of slicing
- 6.6.2.2 End-to-end latency breakdown and programmability consideration
6.6 Network softwarization in 5G mobile networks6.6.1 Network softwarizationIn 5G or IMT-2020 networks, the terminology Network Softwarization is used with the intention to introduce various requirements of programmable software defined infrastructure, especially specific extension for 5G mobile networks. The basic concept of the Network Softwarization is “Slicing” as defined in [ITU-T Y.3011], [ITU-T Y.3012]. Slicing allows logically isolated network partitions (LINP) with a slice being considered as a unit of programmable resources such as network, computation and storage. Considering the wide variety of application domains to be supported by 5G or IMT-2020 network, it is necessary to extend the concept of slicing to cover a wider range of use cases than those targeted by the current SDN/NFV technologies, and the need to address a number of issues on how to utilize slices created on top of programmable software defined infrastructure. 
Figure 2 Network softwarization view of the 5G mobile networks Figure 2 illustrates the network softwarization view of 5G mobile networks, which consists of a couple of slices created on a physical infrastructure by the “network management and orchestration”. A slice is the collection of virtual or physical network functions connected by links to create an end-to-end networked system. In this figure, the slice A consists of radio access network (RAN), mobile packet core, UE(User Equipment)/device and cloud, each of which are collection of virtual or physical network functions. Note that the entities are shown rather symbolically and links are not described in Figure 2 for simplicity. The “network management and orchestration” manages the life cycle of slices: creation, update and deletion. It also manages the physical infrastructure and virtual resources, which are abstraction of physical resources. The physical infrastructure consists of computation and storage resources that include UE/devices (e.g. sensors) and data centers, and network resources that include RATs, MFH, MBH and Transport. It should be noted that both computation/storage resources and network resources are distributed and are available for creating virtual network functions. In addition, the virtualized network functions and network programmability functions assigned to a slice are controlled by the “slice control”. It oversees the overall end-to-end networked system by configuring its entities appropriately. It may include network layer control, and service/application layer control in some cases making 5G network control being service-aware. It depends on the requirements presented for the end-to-end networked system as exemplify by the envisaged natively supported ICN facilities. The orchestration is central to the control and it defined as the sequencing of management operations. A customer may send a request to the “network management and orchestration” with their own requirement of an end-to-end service and steps follows. As such the new 5G control is governing, synchronizing and enforcing the configuration of the natively supported NV / Slicing/ NFV and network programmability facilities in the fronthaul, backhaul, core networks, software-defined clouds and mobile edge computing. This involves:
Services are executed in one (or more) Slices (i.e. a slice is made of a set of VMs) Step 1: Creating a slice Based on the requirement presented, the “network management and orchestration” creates virtual or physical network functions and connects them as appropriate and instantiate all the network functions assigned to the slice. Step 2: (Re-) Configuring the slice The slice control take over the control of all the virtualized network functions and network programmability functions assigned to the slice, and (re-)configure them as appropriate to provide the end-to-end service. 6.6.2 Horizontal extension of slicing6.6.2.1 End-to-end slicingIn 5G mobile networks, the end-to-end communication quality is an important requirement. Especially when wireless technologies are expected to advance, fixed network must support facilitating the advancement of wireless part of end-to-end communications. Therefore, it is natural to consider extending the slicing concept to end-to-end, i.e., from UE to Cloud. Issues in extending slices in 5G mobile networks have then to be addressed, not only software defined infrastructure in a limited part of a network, but also the entire end-to-end path including UE and Cloud. Gap analysis The scope of the current SDN technology primarily focuses on the portions of the network such as data-centres, mobile and core networks. In 5G mobile network, it is necessary to consider end-to-end application quality and enablement through network softwarization platform. Therefore, there exists a gap between the current projection of SDN and NFV technology development and the requirements for end-to-end application quality. The infrastructure for 5G mobile networks is desired to support end-to-end control and management of slices and the composition of multiple slices, especially with consideration of slicing over RATs and fixed parts of end-to-end paths. This gap has been analyzed against what is defined in [ITU-T Y.3300]. 6.6.2.2 End-to-end latency breakdown and programmability considerationAs presented at the pre-meeting of FG IMT-2020 on network softwarization at Turin, Italy, 21 September 2015 [FG IMT-2020 WS 5GMF Nakao], the Figures 3 show the breakdown of the end-to-end latency in the current mobile network architecture. These figures imply that the 5G mobile network architecture must be able to execute network functions and services at any part along the end-to-end communication in order to make the most of wireless latency reduction (targeted from 10msec to 1msec) described in ITU-R IMT Vision [ITU-R IMT Vision].  
Figure 3 End-to-End Latency Breakdown of an example mobile (LTE) network For 3GUMTS/LTE network 3GPP had carried out latency studies which is documented in specifications TR 25.912, TR25.913, TR36.912, TR36.913. 3GPP has carried out study for 5G network requirements, which is documented in TR22.891. Service providers are building LTE network to meet latency budget provided in 3GPP specification, so that services perform optimally. Latency studies carried out on many LTE deployed network demonstrate that 3GPP specifications provides adequate guidelines, however actual LTE network performance varies due to many variables and adjacent ecosystem. For IMT-2020 network our recommendation is to carry out extensive latency study and provide guidelines for latency, packet loss and jitter etc. so that it provide optimal performance for many diverse applications. In order to structure the latency study framework, we suggest break-down network latency into three segments
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