BLE Mesh Overview(2)

BLE Mesh Overview (2)

Flooding:
     Each packet will broadcast to every node in the network until it reaches the target node(s).
Complemented by three types of addressing. “Unicast” (used during initial node set-up), “group”, and
“virtual” (primarily used by  device manufacturers to ‘label’their products).

     Of these, group addressing is the most applicableto everyday operation. A groupaddress is a multicast address which represents one or more elements in the network. The SIG has defined four “Fixed Group Addresses” named “All-proxies”, “All-friends”, “All-relays”, and “All-nodes”
to specifically address the types of nodes defined above.

      In addition to these group addresses, the installer will likely allocate dynamic group addresses
during configuration to reflect the physical mesh layout. For example, dynamic group addresses could be allocated to the lights in each room of a building.

     The specification includes several mechanisms to mitigate advertising and scanning channel congestion. The first is a “Time-To- Live” (TTL) counter that defines how many times a specific packet can be relayed – after a defined number of steps, the packet will not be relayed further.
The second congestion prevention mechanism is a message cache of transmitted packets. A packet can only arrive in the cache once it has circulated completely around the mesh – at which point it can safely be assumed that further transmission is unnecessary. An “optional relaying” feature also limits mesh congestion. By switching off relaying, nodes can receive packets but not
pass them on. Optional relaying adds complexity—because the designer must trade-off mesh flexibility against bandwidth consumption—but in doing so improves overall mesh performance.

Security :
    Provisioning is the process by which otherwise isolated devices become nodes on the mesh network and can be implemented via an app supported on a smartphone or tablet. The process follows five steps: Beaconing (indicating availability to join the mesh); Invitation (from the provisioning device); Public Key Exchange;Authentication; and Session Key Exchange (securing the
subsequent distribution of data to complete provisioning). The provisioning process implements a high degree of security. Thereafter, packets are end-to-end encrypted with AES-128, with privacy enhanced by additional AES-128 encryption between each relay (in part to hide the node addresses). In addition, procedures are included to periodically refresh the encryption keys, and to detect and repel “replay attacks”.


Ref:
      1. ULP Wireless Quarter 10-11
      2. nRF5 SDK for Mesh
      3. Introducing Bluetooth Mesh Networking
      4.How to build a wireless sensor-driven lighting control system based on Bluetooth mesh
         networking - Silvair
      5.2017 Introducing Bluetooth Mesh
      6.Le IoT 想想物聯網 - mesh network topology of BLE 介紹 (1) - Star & Mesh Topology 簡介

BLE 5 Overview

Bluetooth 5 it is highly likely they belong to one or more of these three major advancements:

• 2Mbs for higher throughput and/or energy saving
• 500/125kbs modes for considerably increased range (x4)
• Advertising extensions for increased broadcast capacity (x8)

Advertising extensions :
       Allow add more payload on advertising data packet. by use the secondary
  advertisement channel(previous data channel).enables chaining of advertising packets to create
  greater advertising data payloads of up to 255 bytes.

      Periodic advertisements comprises packets sent at a fixed interval to synchronized devices via
  “connectionless” broadcasting.By using periodic advertisements,scanning devices can more
  consistently “follow” the advertiser and monitor its updates more frequently.

      Connectionless broadcasting is further boosted because Bluetooth 5 features an eight times
  higher broadcast capacity compared to previous versions of the technology.


Ref:
      1. ULP Wireless Quarter 20
      2. Taking a deeper dive into Bluetooth 5
   

     
 

BLE Mesh Overview(1)

    SIG announce the BLE mesh at 2017 July. Not only for BLE 5 but also compatible with BLE4.0 (or later). BLE mesh is implement by add new layers on the BLE physical layer so it need to make appropriate modification on the old BLE 4.0 firmware to get the mesh work.

    Bluetooth mesh follows Bluetooth technology’s architecture whereby GATT
“Profiles”.To avoid GATT Profiles being mistaken for the mesh equivalent, mesh profiles
are called “Models”

The Bluetooth mesh specification details four types
Relay Nodes :
       Relay Nodes re-transmit received packets and are the mechanism by which packets rapidly propagate across the entire network.The downside of relaying is increased current consumption because it relies on the nodes being continuously ‘awake’.

Low Power Nodes & Friend Nodes:
        Low Power Nodes work in tandem with “Friend Nodes”.Friend Nodes are typically
mains powered so can remain permanently awake; the devices cache any messages destined
for the LPN. The LPNs switch to receive’ mode according to a predetermined schedule, accept
cached messages, operate as instructed, and then rapidly return to a power-saving ‘sleep’ state.

Proxy Nodes:
       Proxy Nodes allow devices that run the Bluetooth low energy stack but don’t support Bluetooth
mesh (for example, the current generation of smartphones) to connect to a Bluetooth mesh network. Interaction is achieved via both the node and device’s Generic Attribute Profile (GATT) interface.






Ref:
      1. ULP Wireless Quarter 10-11
      2. nRF5 SDK for Mesh
      3. Bluetooth mesh networking SIG