Release Date：2021-11-30  Author：By Zheng Xingming  Click：

The Need for Deterministic Network

With the development of mobile technologies, mobile network provides not only high-speed Internet services but also communication services for various industries, realizing on-demand services through one network. In the vertical industry, the traditional "best effort" mechanism can no longer meet the demand. In some specific fields such as industrial control, the network needs to support bounded delay and jitter, extremely low packet loss rate, and ultra-high reliability. 

In the early industrial network, dedicated lines were used to meet the transmission requirements of specific service streams. However, with the accelerated development of global science and technology revolution and industrial transformation, industrial Internet has become a key technology of intelligent and information-based industrial manufacturing in the future. In the industrial Internet, IT and OT networks are integrated in one network to meet the large bandwidth required by Internet and information data, as well as the real-time and deterministic requirements of industrial control data. 
In the best-effort network, different data traffic is forwarded in accordance with the QoS scheduling mechanism such as first-in first-out (FIFO) and priority preemption. Under this mechanism, network conflicts cannot be avoided, and it is difficult to provide stable and reliable transmission. Once there is a packet conflict, the packet needs to be waited or retransmitted, which may lead to a long forwarding delay and uncontrollable jitter. This cannot be tolerated in high-precision industrial control, because it may cause errors or even crashes in production systems. To enable mobile networks to provide services for latency-sensitive industries, it is necessary to introduce strict and precise deterministic service guarantee. 

Key Features 
Deterministic network provides deterministic service guarantee for services carried in a network domain, including bounded delay, jitter and packet loss rate. By coordinating the scheduling and forwarding resources of each forwarding node for key traffic streams in the network, it ensures smooth operation and achieves ultra-low delay and anti-jitter forwarding capabilities. In addition, ultra-low packet loss rate and high-reliability transmission can also be achieved through traffic stream replication and multi-link redundancy transmission. The deterministic network of 5G-Advanced will have the following key features (Fig. 1).

Precise Time Synchronization
Nanosecond-level high-precision time synchronization helps each network node obtain consistent time, which not only provides high-precision time consistency checking capability for each service node, but also provides the basis for the scheduling mechanism based on time gating. 
Bounded Delay and Jitter
The enhanced scheduling and forwarding mechanism ensures accurate uplink and downlink bandwidth guarantee, ultra-low latency, and ultra-low jitter forwarding capabilities. For example, it provides end-to-end accurate-time-based resource reservation and scheduling to ensure that every link in the network runs smoothly. It also enhances the priority preemption mechanism, interrupts the forwarding of other packets with low priority at any time, and reduces the waiting delay of packet transmission. 
High-Reliability Transmission
Deterministic network requires uninterrupted services and transmission guarantee with no packet loss. Therefore, the 5G-Advanced network needs to provide all-service, all-state, and all-data real-time hot-backup capability to implement seamless abnormal switching and uninterrupted network services. In addition, the end-to-end dual-path redundancy transmission mechanism also needs to be provided to prevent network service interruption and data loss caused by network faults and packet loss. 
Hybrid Multiplexing
Mobile network is a network with mixed coexistence of multi-service flows, which needs to provide deterministic guarantee for specific traffic flows in multi-service multiplexed networks. For example, there are IT and OT traffic in the industrial Internet, and OT traffic needs to ensure ultra-low delay, jitter, and packet loss rate. The hybrid multiplexing technology of deterministic network greatly reduces the cost of private network deployment and simplifies the complexity of networking. 
End-to-End Closed-Loop Coordination
Deterministic network guarantee cannot be separated from optimized management and coordination of network resources. A comprehensive monitoring mechanism from terminal to network and to service will be further built in a 5G-Advanced network. It will
—provide end-to-end slice management to guarantee SLA.
—implement on-demand network customization through end-to-end coordination among terminals, networks and services.
—perceive network status, service experience and scheduling effect data, adjust service scheduling policies in real time, and construct an end-to-end closed-loop control of "perception-decision-optimization". 

Standards and Evolution
The standards for deterministic network include IEEE 802.1 TSN, IETF DetNet and 3GPP TSC. 
Time sensitive network (TSN) is a L2 Ethernet-based deterministic network standard defined by IEEE. More than 10 specifications related to 802.1 TSN such as 802.1AS, 802.1Qbv, 802.1CB and 802.1Qcc have been released, and they have been relatively mature. The industry has also launched a variety of TSN switches, as well as chips and industrial terminals that support TSN, which are gradually put into commercial use. 
Deterministic networking (DetNet) was set up by IETF in 2015. The standard is still being formulated. Currently, more than 10 RFC specifications, such as Use Case and Data Plane Framework, have been released. Unlike TSN that only supports the L2 Ethernet network, DetNet extends the deterministic network technology to the L3 network of IP/MPLS to achieve deterministic transmission and interconnection with the TSN network, providing a technical basis for deterministic transmission over a wide area. 
Time sensitive communication (TSC) was introduced by 3GPP in the R16 standard released in July 2020. In the R16 standard, the whole 5G system serves as a TSN logical bridge to implement interconnection with the TSN network. In the R17 standard being developed, the 5G system will introduce native determinacy to achieve UE-UE deterministic transmission without interconnection with the TSN network. It is expected that 3GPP will also implement interconnection with the DetNet network in the R18 standard. 

Conclusion
Driven by the digital transformation of industrial networks to the convergence of IT and OT, 5G-Advanced networks will bring advantages such as ultra-low latency and jitter, ultra-high reliability deterministic transmission mechanism, no cabling, flexible deployment and mobility. These advantages will be widely used in smart factories, smart grids, smart ports and other industries.