DECT NR+ : Upper Layer Architecture and Mesh Networking

Point-to-Point

The simplest topology consists of two devices communicating directly.

Typical examples include:

• Sensor-to-gateway links
• Device-to-device control
• Dedicated wireless replacement for wired connections

Star Networks

In a star network, a central device provides connectivity to multiple endpoints.

Characteristics include:

• Centralised radio resource management
• Simple deployment
• Predictable communication paths

Mesh Networks

Mesh networking extends the star concept by allowing devices to act as both clients and routers.

Benefits include:

• Extended coverage
• Increased network capacity
• Self-organisation
• Self-healing operation
• Reduced dependence on a single infrastructure point

Multiple mesh clusters may operate on different channels while remaining part of the same overall system.  

Fixed Termination (FT)

An FT device:

• Controls radio resources
• Manages cluster operation
• Routes traffic
• Often provides backend or internet connectivity

The FT acts as the local coordinator for its cluster.  

Portable Termination (PT)

A PT device:

• Connects to an FT
• Selects the best available parent node
• Sends and receives application data

PT devices can move between clusters as conditions change.  

Dual Role Devices

A device may operate as both FT and PT simultaneously.

This allows a node to:

• Connect upstream as a client
• Provide downstream connectivity to other devices

This capability enables multi-hop mesh networking using a single hardware platform. No specialised router hardware is required.  

Single-Hop View for Applications

Applications see the network as a single logical hop, regardless of how many wireless hops exist underneath.

This simplifies:

• IPv6 integration
• Application development
• Network management

Routing complexity remains hidden within the DECT NR+ protocol stack.  

Uplink Routing

Uplink traffic refers to data travelling from devices toward the backend.

Examples include:

• Sensors sending measurements
• Asset trackers reporting status
• Industrial equipment sending telemetry

Uplink routing uses a cluster-tree structure.

Each device only needs to know:

• The best next hop
• Signal quality
• Route cost

Devices continuously reassess available routes and can change paths when network conditions change. 

Route Cost

Route selection can consider factors such as:

• Number of hops
• Link quality
• Device load
• Available power

For example, mains-powered routers may be preferred over battery-powered devices to reduce battery consumption throughout the network.  

Downlink Routing

Downlink traffic refers to data travelling from backend systems to devices.

Examples include:

• Configuration updates
• Commands
• Firmware delivery

DECT NR+ uses controlled flooding techniques to distribute downlink traffic efficiently through the mesh while minimising unnecessary transmissions.  

Local Device-to-Device Communication

The protocol also supports local communications that never leave the wireless network.

Examples include:

• Lighting control
• Building automation
• Local industrial control systems

These messages can be:

• Unicast
• Broadcast
• Multicast

This allows fast local control without involving cloud services or backend infrastructure.  

Self-Healing Operation

DECT NR+ mesh networks are designed without a central mesh controller.

As a result:

• No single routing coordinator exists
• No single point of failure is required
• Devices continuously evaluate alternative routes

If a router or gateway becomes unavailable, devices can select new paths and continue operation automatically. This provides inherent self-healing behaviour and improves overall network resilience.  

CVT Layer

The Convergence Layer (CVT) sits closest to applications.

Its functions include:

• Application multiplexing
• End-to-end security
• Segmentation and reassembly
• End-to-end retransmission

IPv6 is treated as an application running on top of the radio system rather than being deeply embedded into the radio architecture. This allows both IP-based and non-IP applications to coexist within the same network.  

Data Link Control (DLC)

The DLC layer provides:

• Routing services
• Quality of Service (QoS)
• Packet forwarding
• Hop counting
• Delay tracking
• Retransmission management

This layer manages traffic movement through the mesh while maintaining reliability and prioritisation. 

MAC Layer

The MAC layer is responsible for:

• Data multiplexing
• Transmission scheduling
• Link-level security
• Error recovery
• Link adaptation
• Power control

It determines how information is transmitted over the air and how radio resources are allocated.  

End-to-End Security

The CVT layer supports:

• Encryption
• Integrity protection
• Independent security domains

Different applications can use different security keys within the same network. This allows multiple services to coexist securely.  

Link-Level Security

The MAC layer provides additional protection between neighbouring nodes.

This ensures:

• Secure wireless links
• Protection against local interception
• Secure forwarding through multi-hop networks

Together, end-to-end and link-level security create a defence-in-depth approach suitable for professional IoT and industrial deployments.  

Cluster-Based Resource Control

Each FT independently manages radio resources for its own cluster.

Benefits include:

• Improved scalability
• Reduced coordination overhead
• Better spectrum utilisation
• Support for very large deployments

Clusters may select different operating channels to reduce interference.  

Random Access

Random access is used for:

• Initial network attachment
• Device discovery
• Small, sporadic transmissions

The mechanism uses Listen Before Talk (LBT).

Process:

• Device listens to the channel.
• If the channel is clear, it transmits.
• If busy, it waits for a random backoff period.
• The process repeats until transmission succeeds.

Collision probability is reduced through adaptive backoff timing.  

Scheduled Access

Scheduled access is intended for predictable traffic patterns.

Examples include:

• Audio
• Video
• Industrial control
• Periodic sensor reporting

The FT allocates transmission opportunities to devices, creating deterministic communication behaviour and efficient spectrum utilisation.