| Internet-Draft | Hierarchical IETF Network Slices | October 2021 |
| Dong & Li | Expires 28 April 2022 | [Page] |
Network slicing is targeted at existing or emerging customers or services which may request for network connectivity services with a specific set of Service Level Objectives (SLOs) and Service Level Expectations (SLEs). The framework of IETF network slice can support hierarchical network slicing. And in some network scenarios, there may be requirements for the deployment of hierarchical network slices.¶
This document describes the typical scenarios of hierarchical IETF network slices, and provides the considerations and requirements on the technologies in different network planes to support hierarchical network slicing.¶
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Network slicing is targeted at existing or emerging customers or services which may request for network connectivity services with a specific set of Service Level Objectives (SLOs) and Service Level Expectations (SLEs). The concept and general framework of IETF network slice are described in [I-D.ietf-teas-ietf-network-slices]. [I-D.ietf-teas-enhanced-vpn] describes the framework and technologies which can be used for IETF network slice realization by utilizing VPN and Traffic Engineering (TE) mechanisms with enhancements that specific services require over traditional VPNs.¶
[I-D.ietf-teas-ietf-network-slices] mentions that IETF Network Slices may be combined hierarchically, which means that a network slice may itself be further sliced. However, there is no detailed description about hierarchical IETF network slices scenarios and requirements.¶
This document describes the typical scenarios in which the deployment of hierarchical IETF network slices may be needed. This document also provides the considerations and requirements on the technologies in different network planes to support hierarchical network slicing.¶
In this section, several network scenarios of hierarchical IETF network slicing are introduced.¶
One of the typical network slice deployment is in the multi-industrial network case, in which a physical network is used to deliver services of multiple vertical industries. Separate IETF network slices are provided for different industries, such as health-care, education, manufacturing, governmental affairs, etc. Then within the network slice of a specific industry, there may be need to create separate network slices for some or all of the customers within this industry.¶
For example, within the education network slice, some of the universities may require for a separate network slice to connect with a set of the branch campuses. Another examples is within the health-care network slice, some of the hospitals may require for a separate network slice for the connectivity and services between a set of the branch hospitals.¶
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Figure 1. Hierarchical Network Slices: Scenario 1
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Another network slice deployment case is to provide dedicated IETF network slices for some important customers as the first-level network slices. While the customers may require to further split their network slices into different sub-network slices for different applications.¶
For example, a network slice for a hospital may be further divided to carry different type of medical services, such as remote patient monitoring, remote ultrasound diagnose, medical image transmission etc.¶
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Figure 2. Hierarchical Network Slices: Scenario 2
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IETF network slice can also be delivered as a wholesale service to other network operators. In this case a network operator can be the customer of a network slice, and it may also need to deliver IETF network slice services to its customers. This is similar to the Carrier's Carrier VPN service mode, while some additional requirement on the SLOs and SLEs may be required by the second-level network slice customer.¶
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Figure 3. Hierarchical Network Slices: Scenario 3¶
To support the realization of hierarchical network slices, it is expected that there will be specific requirements on the technologies used in each network plane. In this section, the requirements of hierarchical network slicing on the forwarding resource partitioning, the data plane encapsulations, the control plane protocols and the management plane are analyzed.¶
For the realization of IETF network slices, the network resources in the underlying forwarding plane needs to be partitioned into different subsets, each subset is used to build the underlay construct to support one or a group of IETF network slice services. In order to support hierarchical network slices, the forwarding plane resources needs to be able to be partitioned in a hierarchical manner. Taking a two-level hierarchical network slice as an example, the bandwidth resource of a physical interface needs to be partitioned in two levels. There can be different options in the modeling the interface bandwidth resource partitioning.¶
The first option is to treat the first-level network resource partitions as a set of layer-3 interfaces or sub-interfaces with dedicated network resources, and the second-level network resource partitions are represented as virtual layer-2 data channels, as shown in the figure below:¶
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Figure 4. Modeling of Interface Resource Partition: Option 1
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The second option is to treat the first-level network resource partitions as a virtual layer-2 sub-interface of the layer-3 interface, and the second-level network resource partition is represented as a virtual data channel under the virtual layer-2 sub-interface, as shown in the figure below:¶
+----------------------+ | +----------------+ | | | +------------+ | | | | |Data Channel| | | | | +------------+ | | | | ... | | | | +------------+ | | | | |Data Channel| | | | | +------------+ | | | +----------------+ | | layer-2 subinterface | | | | . . . | | +----------------+ | | | +------------+ | | | | |Data Channel| | | | | +------------+ | | | | ... | | | | +------------+ | | | | |Data Channel| | | | | +------------+ | | | +----------------+ | | layer-2 subinterface | +----------------------+ Layer-3 Physical Interface Figure 5. Modeling of Interface Resource Parition, Option 2¶
The options of the resource partition modeling may have impact to the amount of information to be distributed in the control plane. Depends on the network deployment requirements, different resource partition modeling options may be used.¶
Traffic of IETF network slices can be steered into the corresponding virtual underlay construct based on one or multiple fields in the data packet, so that the set of network resources are used for processing and forwarding the packet. On the network edge nodes, traffic flows can be classified and mapped to IETF network slices based on the matching rules according to operators' local policy. While on the intermediate nodes, a dedicated data plane identifier can facilitate the identification of the set of network resources associated with the virtual underlay on the network nodes for packet processing.¶
For hierarchical network slices, such data plane identifiers may need to be able to identify both the first-level resource partition and the second-level resource partition. There are several options for the data plane resource identifier for hierarchical network slices.¶
The first option is to use a unified identifier for both the first-level resource partition and the second-level resource partition. In this case, the first-level resource partitions and the second-level resource partitions are identified by distinct identifier values.¶
+-----------------------------------------+ | Unified Resource ID for different levels| +-----------------------------------------+ Figure 6. Unified Resource ID¶
The second option is to use a hierarchical identifier for the first-level resource partition and the second level resource partition. In this case, the first part of the Resource ID is used to identify the first-level resource partition, and the second part of the resource ID is used to identify the second-level resource partition. Depends on the data plane technologies used, the hierarchical resource identifier may be positioned in a continuous field in the packet, or maybe positioned in separate fields.¶
+--------------------+--------------------+ | Level-1 Resource ID| Level-2 Resource ID| +--------------------+--------------------+ Figure 7. Hierarchical Resource ID¶
The control plane may be used for the distribution of the resource partition information and the associated data plane identifiers among the network nodes and to the network controller. With different resource partition modeling, the information may be advertised as either layer-3 or layer-2 network information, which can have different scalability implications to the control plane. As the number of both the level-1 network slices and level-2 network slices increases, some control plane mechanisms may be needed to adopt to the amount of network slice information to be advertised.¶
Depends on the scenarios of hierarchical network slicing, the management system of network operator may need to support additional functions and procedures for the life-cycle management of hierarchical network slices. The detailed analysis about the requirement on management plane is for further study.¶
This document makes no request of IANA.¶
Zhibo Hu Email: huzhibo@huawei.com¶
The authors would like to thank XXX for the review and discussion of this document.¶