Segment routing over IPv6 (SRv6) is a technology used to forward data packets in the IPv6 network based on the source routing concept. It combines the two most popular network technologies: segment routing and IPv6.
The native IPv6 attribute of SRv6 ensures the reachability to any network node while its powerful network programming capability can better meet the SLA requirements of network services, making it the most promising network technology in the IPv6 era.

Major Advantages of SRv6
Simplification of Network Protocols
SRv6 removes requirements for MPLS tunneling technologies such as LDP and RSVP-TE through an extension of IGP/BGP, simplifying the control plane. It uses an IPv6 address as the label for packet forwarding in place of an MPLS label on the data plane. On both the control plane and the data plane, unified transport is implemented, greatly simplifying network protocols, reducing the complexity of operation and maintenance, and allowing the cloud, network and terminals to implement an end-to-end manageable and controllable solution based on the same standard protocol. It also enables flexible front-line access to multiple clouds and agile service provisioning. 
Native IPv6 Attribute 
SRv6 uses an IPv6 extension header without changing the IPv6 encapsulation structure, assuring compatibility with the existing network. SRv6 relies on the IPv6 reachability to implement interworking between IPv6 nodes, making its cross-domain deployment simpler. In the packet forwarding process, the intermediate node only needs to support IPv6 forwarding and needs not to support a special forwarding logic so that SRv6 can break the boundary between the operator network and the data center network and be deployed in the data center network, which greatly enhances the extensibility and deployment flexibility of SRv6.
Network Programmability 
SRv6 network programming requires an SRv6 header (SRH), which has three layers of programming space (Fig. 1).

Applications of SRv6 in 5G-A Core Network
The above advantages of SRv6 make the network more concise and intelligent, and make it the core technology and hotspot of IPv6+. It breaks the boundary between cloud and network and extends the network to user terminals so that an operator's network is not pipelined. It also helps operators rapidly develop intelligent cloud networks, realize application/user-level network SLA guarantee, and obtain more value.
The 5G/IoT/Cloud service requires the network to be highly scalable, maintainable, deterministic, stable and secure. A 5G-A core network only needs to expand UPF and SMF to support SRv6 and match these requirements:
Based on SRv6, a SID locator can be used as the unique identifier for a virtual network slice, identifying the network resources allocated to the slice. In data forwarding, the SRv6 SID identifies the virtual network that the packet belongs to, and indicates the topology and resources to be used for data forwarding. Based on the unified network infrastructure, differentiated forwarding paths and isolated network resources can be provided for different network slicing services, ensuring isolation between network slices both in terms of traffic and security policies and avoiding inter-slice interference.
SRv6-based SFC can be implemented by inserting SIDs related to SF into the SID list of the SRv6 header, and integrate the overlay, underlay and service chaining based on the SRv6 traffic engineering capability. The SRv6 technology has lower requirements for SF equipment (supporting IPv6 forwarding or L2 transparent transmission) and is more universal in delivering SFC. The SRv6-based service chain can support both SR-aware and SR-unaware services, and can be deployed on any network supporting IPv6 to connect high-performance, high-reliability dedicated hardware to the cloud network.
SRv6-based DetNet encapsulates data in the SRv6 header, and encodes explicit paths in the SRH to provide a stable forwarding service and to ensure that DetNet service is not affected when the network topology changes. Other functions/parameters for service protection (packet replication, elimination and ordering) and congestion control (packet queuing and forwarding) are defined in SRH, which gives supports to DetNet path redundancy and congestion protection. Thus, deterministic network services with bounded latency, low jitter and zero packet loss can be provided for high-value service flows.
APN6 uses SRv6 packets to convey application information into the network, allowing SLA requirements from applications to be perceived by the network in a native way. According to the application information carried in the packets, the network is able to apply the corresponding policy, dispatch the traffic, adjust the resources, and select the corresponding SRv6 path (such as low-latency path), providing SLA guarantee and appropriate network services to applications. APN6 achieves seamless combination of network capability and service requirements so that the network can sense the applications' requirements, provide high-quality differentiated services, and realize streamlined operation.

As a basic technology for future networks, SRv6 is developing at a high speed. In 2020, ZTE supported China Telecom to realize the world's largest commercial SRv6 network. With rapid development of 5G/IoT/Cloud services, SRv6 will certainly play a more important role. The IPv6+ innovation represented by SRv6 is leading the transformation of the future network from the interconnection of all things to the "intelligent" connection of all things.