Thread Group (https://www.threadgroup.org/) was founded on July 15, 2014 by Silicon Labs (aka “Silicon Technology”) and six other companies. As a non-profit organization, the Thread Group focuses on promoting the application of Thread in the Internet of Things, educating developers and consumers about Thread technology and its advantages, and providing rigorous product certification testing to ensure the ultimate user experience. This article will give a brief introduction to Thread network technology and key features.

Threadwhat is it?
Thread is a secure wireless mesh networking protocol. Thread addresses emerging needs in building a network of smart home products. Based on 6LoWPAN, Thread fully utilizes open standards and IPv6 technology, and has many technical advantages over other wireless standards: security and reliability, no single point of failure, simple connection, and low power consumption. Product developers and consumers can easily and securely form a low-power wireless mesh network of more than 250 devices through Thread, and every device in the network can connect to the Internet and access cloud services. The Thread stack is an open standard built on an existing set of standards from the Institute of Electrical and Electronics Engineers (IEEE) and the Internet Engineering Task Force (IETF), rather than a completely new standard (see figure below).

picture1. ThreadProtocol stack overview Threadgeneral characteristics of
The Thread protocol stack supports IPv6 addresses and enables low-cost bridging with other IP networks, making it the best choice for low-power/battery-powered operation and communication between wireless devices. The Thread protocol stack is designed for smart home and business applications based on IP networks, and can be combined with various application layers on the protocol stack. The general characteristics of the Thread protocol stack are as follows:

Simple and convenient network installation, startup and operation:The Thread stack supports a variety of network topologies. Installation is easy and convenient from a smartphone, tablet or computer. The product installation code ensures that only authorized devices can join the network. When routing problems arise, simple protocols for building and joining networks allow the system to configure itself and fix those problems.

safety:Devices cannot join the network unless authorized, and all communications are encrypted and secured. Security protection can be used at the network layer as well as at the application layer. All Thread networks are encrypted with an authentication scheme and Advanced Encryption Standard (AES). Thread networks are more secure than other wireless networks evaluated by the Thread Group.

It can take into account the needs of home network of all sizes:The number of devices on different home networks varies greatly, ranging from a few to hundreds. The network layer design is designed to optimize network operation based on the intended use.

For large business networks:For large commercial networks, a single Thread network is not sufficient for all applications, systems and networks. The Thread Domain Model allows scaling to up to 10,000 Thread devices in a single deployment, which is achieved by combining different connectivity technologies (Thread, Ethernet, Wi-Fi, etc.).

Two-way communication service discovery and connection:Multicast and broadcast are less efficient for wireless mesh networks. For communication with the outside world of the mesh network, Thread provides a communication registration service, the device can register whether it is available and whether it can provide communication services, and the client can use unicast query to find the registered service.

Wide coverage:The coverage area of ​​a typical Thread device is usually sufficient for the average household. A design with a power amplifier can greatly improve coverage. The use of distributed spread spectrum technology in the physical layer (PHY) can better improve the anti-interference ability. For commercial networks, the Thread domain model allows multiple Thread networks to communicate with each other through the backbone network, so it can be extended to cover multiple Mesh subnets.

No single point of failure design:The Thread stack is designed to operate safely and reliably, even in the event of a single device failing or missing. Thread devices can also incorporate IPv6-based links, such as Wi-Fi and Ethernet, into the topology to reduce the likelihood of multiple Thread partitions. This allows Thread devices to take advantage of the higher throughput, larger channel capacity, and wider coverage of these infrastructure links, while still supporting low-power devices.

Low power consumption:The device communicates with high efficiency, and the expected service life of the device can reach several years under normal battery usage conditions, so the user experience is improved. With the right duty cycle, the device can typically run for years on AA size batteries.

Cost-effective:Compatible chipsets and software stacks from multiple vendors are priced for mass deployment and are designed for ultra-low power consumption.

ThreadHome Network Architecture
Users communicate with the home Thread network from their own device (smartphone, tablet or computer) via Wi-Fi on their home local area network (HAN) or using a cloud-based application. The following diagram illustrates the main device types in the Thread network architecture.

picture2. ThreadHome Network ArchitectureA Thread network consists of the following device types:

Border router:Supports network connections between 802.15.4 networks and other adjacent physical layers (Wi-Fi, Ethernet, etc.). Border routers provide services to devices within an 802.15.4 network, including routing services and service discovery in offline operation. There can be one or more border routers in a Thread network.

LeaderLocated in the Thread network, it manages the assignment and registration of router IDs, and accepts requests from router-compliant end devices (REEDs) to become routers. The Leader decides which devices should be routers, and, like all routers in the Thread network, the Leader can also have child devices. Leader also assigns and manages router addresses through CoAP (Constrained Application Protocol). However, all the information contained in the Leader is also stored in other Thread routers. Therefore, if the leader fails or loses connection to the Thread network, another Thread router can be elected as the leader without user intervention.

Threadrouter:Provides routing services for network devices. Thread routers also provide join and security services for devices trying to join the network. Thread routers cannot sleep and can also become REED by downgrading their functionality.

REEDCan be a Thread router or Leader, but not necessarily a border router with special properties such as multiple interfaces. REEDs cannot be routers in network topology or other specific situations. REED does not relay messages and does not provide join or security services to other devices in the network. If necessary, the network manages router-eligible devices and upgrades them to routers without user intervention.

Terminal Equipment:End devices that do not qualify as routers can be either FED (full end device) or MED (minimal end device). The MED does not need to be synchronized with the parent device to communicate.

dormant terminal device(SED): Communicates only through the Thread router parent device and cannot relay messages for other devices.

Synchronous sleep end device(SSED): is a type of dormant end device that uses CSL in IEEE802.15.4-2015 to keep synchronization with the parent device without using regular data requests.

Threadbusiness network architecture
Thread’s commercial networking model employs the same major types of devices as home networking, and introduces new concepts. The user communicates with the business network through a device (smartphone, tablet or computer) via Wi-Fi or a corporate network. The following figure illustrates the business network topology.

picture3. Threadbusiness network architectureBusiness Network Architecture Concepts:

Threaddomain modelSupports seamless integration of multiple Thread networks, as well as seamless connection to non-Thread IPv6 networks. The main benefit of Thread Domains is that devices have a certain degree of flexibility to join an available Thread network configured with a public Thread Domain, which reduces manual network planning or costs as the network scales up or the amount of data expands. High costs for manual reconfiguration.

Backbone Border Router(BBR) is a border router used in commercial networks that facilitates synchronization of Thread domains across multiple network segments and allows extensive multicast propagation to and from each individual network in a Thread domain. A Thread network belonging to a larger domain must have at least one “primary” BBR, and can have multiple “secondary” BBRs for fail-safe redundancy. Individual BBRs communicate with each other through a backbone that connects all Thread networks.

picture4. Threaddomain model No single point of failure

The Thread stack is designed to avoid a single point of failure. While there are many devices in the system that perform special functions, Thread networking enables these devices to be replaced without affecting the network or the continued operation of the device. For example, if a dormant end device requires a parent device to communicate, then the parent device becomes a single point of failure for communication. However, in a Thread network, a sleeping end device can choose another parent device when its parent device is unavailable. And this conversion process is invisible to the user. Although the Thread system is designed with no single point of failure, in some topologies, individual devices do not have backup capabilities. For example, in a system configured with a single border router, if the border router loses power, there is no way to switch to the alternate border router. In this case, the border router must be reconfigured. With Thread Specification 1.3.0, border routers sharing infrastructure links can improve single-point-of-failure-free designs across mediums such as Wi-Fi or Ethernet by leveraging Thread Radio Encapsulation Links (TREL). With this feature, the possibility of forming Thread partitions across links is reduced.

Summarize

This article mainly introduces the general characteristics of Thread, the network architecture of Thread, and the very important no single point of failure feature in the Thread protocol.

Editor: Huang Fei

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