T-SRv6: SPN Computing Network Solution for Slicing Transport Network

Computing networks, curcial for driving high-quality digital economy development,  are highly favored by major telecom operators for their promising prospects. Building capabilities centered around computing power presents operators with vital opportunities for transformation and upgrading, as well as reconstructing industrial value ecosystems. Slicing packet network (SPN), a key component of computing networks, mainly provides flexible access to computing services for users. It also offers ubiquitous computing power scheduling for cloud-edge and edge-edge collaborations, catering to diverse computing connectivity needs across vertical industries. Additionally, SPN requires evolving capabilities in perception and routing within computing networks, meeting the needs that computing networks evolve to computing-network integration.

Currently, computing services in computing networks are primarily deployed in provincial/regional data centers. Accessing computing resources from the metro SPN network necessitates coordinated scheduling across multiple networks, including the metro SPN network and provincial/inter-provincial backbones (such as China Mobile’s cloud private network), reach the data center. Therefore, SPN needs to support SRv6 capabilities to achieve interoperability with cloud private networks, providing users with end-to-end service provisioning and O&M capabilities for one-hop SRv6-to-cloud connectivity. As a transport network, SPN needs to consider the following factors in its evolution to support SRv6:

• Inheriting transport service features: When accessing computing services on the SPN network, the computing connection must have transport features, such as bidirectional same path, bidirectional delay symmetry, carrier-class protection switching, and hard slice isolation capabilities.
• Encapsulation efficiency and forwarding performance: The SPN network should minimize additional SRv6 encapsulation overhead and associated forwarding performance degradation.
• Complexity in upgrading the existing network: The SPN network should smoothly evolve to support SRv6 capabilities, avoiding intricate reconstruction and minimizing impact on existing services.

T-SRv6 Solution Overview

ZTE innovatively proposes the transport-segment routing IPv6 (T-SRv6) solution, tailored to the diverse requirements of computing services and the current state of the SPN network, for implementing the SRv6 technology.

T-SRv6, integrating transport network features, deploys nodes at the SPN network edge, enabling complete T-SRv6 capability without upgrading internal nodes. With minimal upgrades or additions to edge nodes, the entire network achieves end-to-end SRv6 one-hop cloud computing connectivity from metropolitan to provincial backbone.

Fig. 1 shows the T-SRv6 solution architecture, employing a hierarchical management and control architecture and service model due to the distinct domains of the metro SPN and intra-province/inter-province backbone. The cross-domain orchestrator identifies domain border nodes and links. Each domain’s SPN/cloud private network controller computes and configures the forwarding path, and reports the binding SID (BSID) indicating the intra-domain path to the orchestrator. The orchestrator orchestrates the BSID into an end-to-end SRv6 policy path. Since the intra-domain forwarding path indicated by the BSID is configured by each domain controller and remains invisible to external networks, SRv6 programmable technology is used to associate the BSID with SR-TP or MTN channel within the domain. In this way, the SPN network can achieve SRv6 capability only at border nodes while maintaining existing SR-TP or MTN channel forwarding mechanisms within the domain, thus creating an SPN SRv6 solution with transport features.

Key T-SRv6 Features

The T-SRv6 solution supports flexible and programmable capabilities defined by the standard SRv6 solution. It can interoperate with networks like the intra-province/inter-province cloud private networks of China Mobile, exclusively supporting the standard SRv6 solution. Moreover, it combines SRv6 and transport network technologies, constituting an SRv6 solution with transport network features. Compared with the standard SRv6 solution, T-SRv6 stands out with key features such as flexible slicing, efficient forwarding, bidirectional same path, and agile deployment.

• Flexible Slicing to Meet Diverse Computing Connectivity Needs Across Industries

The SPN network supports metro transport network (MTN)-based slicing technology, offering soft-isolated high-reliability SR-TP connections and flexible SR BE connections in a shared slice, or hard-isolated MTN channel connections in an exclusive slice. With SRv6’s programmable capability, it can bind SRv6 to SR-TP tunnel in the SPN network using the Endpoint bound to an SR-MPLS policy (End.BM) defined by RFC 8986, providing a soft-isolated slice channel with statistical multiplexing and QoS bandwidth guarantee to the computing network. In addition, the T-SRv6 solution extends the standard SRv6 solution by defining the endpoint bound to a cross-connect channel (End.BXC) function to bind SRv6 to MTN channel hard isolation slice channels in the SRv6 network, providing lossless and deterministic hard isolation connections to the computing network. This approach enables end-to-end SRv6 binding to different types of slicing channels within the SPN network, meeting the differentiated SLA requirements of various industry applications.

• Efficient Forwarding to Give Full Play to Existing Network Capabilities

Due to its hierarchical architecture, cross-domain SRv6 uses two types of packet encapsulation: end-to-end SRv6 and intra-domain encapsulation. In the T-SRv6 solution, end-to-end SRv6 employs general SRH encapsulation for interworking with heterogeneous networks. Within the SPN domain, T-SRv6 uses SR-TP label stack or MTN frame encapsulation. Given the SPN’s strict constraint paths, SR-TP encapsulation involves a 4-bytes constraint label at each hop, enhancing encapsulation efficiency through label stripping during forwarding. In contrast, hop-by-hop SRv6 encapsulation includes a 16-byte constraint label along with an additional 48 bytes for IPv6 header and SRH header encapsulation. Therefore, hop-by-hop SRv6 exhibits significantly lower encapsulation efficiency compared to the T-SRv6 solution. Although G-SRv6 utilizes the header compression technology to reduce per-hop constraint encapsulation to 4 bytes like T-SRv6, its encapsulation efficiency remains relatively low due to IPv6 header and SRH encapsulation overhead. Fig. 2 compares encapsulation efficiency in different packet lengths, using a 10-layer constraint label as a reference.

Enhanced encapsulation efficiency not only boosts effective bandwidth utilization but also improves forwarding performance. This avoids performance degradation  caused by the need for internal chip processing when encapsulated bytes exceed the processing capacity of the device chip.

• Bidirectional Same Path to Meet Application Needs of Delay-Symmetric Industry

In the T-SRv6 solution, transport network technology features are reserved in the SPN network. The forwarding paths of SR-TP and MTN channel are bidirectionally the same. Moreover, the protection mechanism implements bidirectional protection switching through the APS protocol to ensure that the forwarding paths are bidirectionally the same after the switching. This approach offers natural advantages for certain industrial applications, like grid differential protection signals, which demand bidirectional delay symmetry.

• Agile Deployment for Rapid Computing Service Provision

In the T-SRv6 solution, only edge nodes in the SPN network need to support T-SRv6 capability, with no need to upgrade forwarding nodes. In a typical cloud service activation scenario, the SPN network simply adds a pair of termination devices connected to the cloud private network, or upgrades existing termination devices in the SPN core layer. At the same time, SPN CPE supporting T-SRv6 capability is deployed on the client side of the cloud service. Other network devices remain unchanged. This enables end-to-end SRv6 one-hop connectivity to the cloud, facilitating rapid provisioning of computing connection services (Fig. 3).

• Continuous Evolution to Meet Full Lifecycle Needs of Computing Networks

In the future, computing networks will evolve to computing-network integration, requiring devices connected to computing resources (such as edge cloud) in the computing network to possess computing perception and reporting capabilities. These devices must also support computing routes and implement route search and forwarding based on the computing power. The choice of forwarding method for nodes within the network does not affect the functionality and applications of the computing network. By upgrading SPN network edge nodes, the T-SRv6 solution can meet the future requirements of computing-network integration for computing scheduling.

SRv6 Trial on Existing SPN Network

To achieve the vision of “ubiquitous network, computing power, and intelligence”, China Mobile has actively researched computing network technologies. In the SPN network domain, China Mobile Research Institute formulated the Technical Specification for SPN Computing Network Perception Equipment in the first half of 2022. In August 2022, in collaboration with ZTE, China Mobile trialed the T-SRv6 solution on its existing SPN network in Guangdong. This marks the first SPN SRv6 trial with existing network services in China, verifying the agile SRv6 deployment capability on the SPN network and its ability to open flexible slice channels through programmable technology.

To further verify end-to-end interoperability between the SPN T-SRv6 solution and the cloud private network, China Mobile and ZTE jointly conducted cross-domain SRv6 interoperability tests integrating SPN with the cloud private network in Zhejiang Provence. Utilizing an orchestrator, they orchestrated cross-network services between SPN and the cloud private network, confirming the end-to-end SRv6 one-hop cloud service provisioning capability of SPN T-SRv6 and the cloud private network.

The successful T-SRv6 trial on China Mobile’s existing SPN network verifies the feasibility and advancement of the SPN T-SRv6 solution, making a significant step towards its commercial use.