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Understanding Thread Protocol Cheat Sheet by

connectivity     protocol     ipv6     thread


Thread is a simpli­fied, IPv6-based mesh networking protocol developed for connecting products around the home to each other, to the internet, and to the cloud. Thread is simple to install, highly secure, and scalable to hundreds of devices. It uses low-da­ta-­rate, low-cost, low-power 802.15.4 chipsets.

Thread’s focus on mesh networ­king, native support for Internet Protocol (IP), ultra-low power, and reliab­ility delivers on the promise of seamless connec­tivity among “things” in the IoT. Thread enables efficient commun­ication between connected devices and a simple yet robust interface to the cloud. Thread protocol offers a compelling wireless mesh networking solution by delivering the following seven benefits for the connected home:

1. Standa­rds­-based protocol

Open, standa­rds­-based protocols reap the benefits of technical peer reviews, cross-­vendor intero­per­abi­lity, and compet­ition. Thread is based on a foundation of IEEE and IETF standards, including IEEE 802.15.4. The official Thread specif­ication was published by the Thread Group on July 13, 2015, and beta certif­ication has opened.

2. Simplified config­uration

Thread eliminates the comple­xities of prior mesh networking standards by supporting two node types: Router Eligible or End Device. Router Eligible nodes become routers when needed to support the mesh. The first Router Eligible node to form the network is autono­mously designated a router as well as the Leader. A Leader performs additional network management tasks and makes decisions on behalf of the network. Other Router Eligible nodes can autono­mously assume the role of a Leader, but there’s only one Leader per network at a time.

Nodes that join as End Devices send messages to a router designated as its “parent,” and the parent performs routing operations on behalf of its “child.” End Devices route commun­ication through parents and can be programmed to be “sleepy” to reduce power consum­ption. End Devices that cannot commun­icate with their parent after multiple attempts will autono­mously search and attach to a new parent.


3. IP-based messaging

Since Thread provides native support for IP, all devices in a Thread network have an IPv6 address and can be accessed directly by local devices on a home area network (HAN) or off-ne­twork using Thread­-ca­pable IP routers called border routers.

Nodes on the network form IPv6 global addresses from prefixes assigned by border routers, or locally by a self-a­ssigned prefix to form a Unique Local Address (ULA). Routing IDs used in the network are assigned by the Leader. Thread leverages User Datagram Protocol (UDP) for messaging instead of its heavier altern­ative, Transm­ission Control Protocol (TCP). Unlike TCP, UDP is a connec­tio­nless protocol that forgoes TCP features — such as error-­che­cking, packet­-se­que­ncing, and retran­smi­ssions — in exchange for faster, more efficient transm­ission. This efficiency equates to less overhead, which is critical for batter­y-p­owered, resour­ce-­con­str­ained devices.

4. Low-power operation

Thread supports low-power operation using sleepy end nodes, which are devices that spend the majority of their time in a low-power sleep state. With Thread, sleepy devices are not required to check in with the network. Messages for sleepy devices are buffered by their parents. Message transm­ission is triggered only after a sleepy device wakes up and polls its parent for inbound messages.

5. Scalable and resilient

Thread can support networks of 250+ nodes. In a Thread network, the maximum number of active routers is 32. Routing inform­ation can be effici­ently distri­buted across the network, and all routers maintain visibility of all routes within the network. As nodes are added to the network and the topology changes, the network adapts by exchanging Mesh Link Establ­ishment (MLE) messages. Additional routers can be added autono­mously if there are Router Eligible devices operating as end devices. These devices “listen” to routing messages and petition the network Leader to become a router when necessary to improve network perfor­mance.

Thread is a robust, self-h­ealing mesh network with no single point of failure. If a router fails, the network dynami­cally reroutes traffic around the failed node. If a Leader fails, another router is autono­mously elected the new Leader. Multiple border routers provide fail-safe redundancy for off-ne­twork commun­ica­tion.

6. Intero­perable

The Thread Group has defined a standard test harness to be used for certif­ication of all Thread stacks and final Thread products. This test harness is provided to Thread Group member companies for develo­pment and testing of software prior to certif­ica­tion.

7. Secure and User-F­riendly

Thread networks are built to be simple to use, yet extremely secure. Thread uses AES-128 to protect networking transa­ctions at the MAC level and uses a combin­ation of ECC and J-PAKE algorithms to securely add devices to a network. Applic­ations have the option to use standa­rds­-based IP security protocols to secure applic­ation payloads.

The Thread network assumes a commis­sioning device is available for a user to add any new devices to the network. Thread makes it possible to designate off-ne­twork devices — such as smart phones, computers, and on-network Thread devices — as commis­sio­ners. To join a Thread network, a user instructs the commis­sioning device that a new device is being added and inputs a unique passphrase associated with the joining device. This passphrase establ­ishes a secure datagram transport layer security (DTLS) session to authen­ticate and authorize the joining device, and that device is then granted access to the Thread network. Once the device is added, the commis­sioning device is no longer needed.

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