DECT NR+ standard upper layers technology FAQ blog

Monday 30 October 2023

The third webinar in the DECT NR+ series took a deeper dive into the technology. Juho Pirskanen from Wirepas explained to the audience about the system topologies, potential use case deployments, forming and routing in a mesh network, end-to-end protocol functions, link specific functions, and details on channel access.

The audience was captivated and requested more detailed information with the following questions:- 

Used Abbreviations According to TS103.636-4 MAC specification

FT stands for a Fixed Termination point. A Fixed Termination point (FT) is an operational mode of a radio device (RD) where the RD initiates, co-ordinates local radio resources and provides information on how other RDs may connect and communicate with it.

PT stands for Portable Termination point. A Portable Termination point (PT) is an operational mode of a radio device (RD) where the RD selects another RD, which is in FT mode, for association.

 
RD stands for Radio Device. An RD operating in mesh network can operate in both FT and PT mode simultaneously. An RD operating with an external interface to backend systems operates in FT mode. 

Back-end support

Can the mesh have multiple back-ends?

Yes. The gateway can have connectivity to multiple back-ends and can steer traffic based on end-point multiplexing values to different back-ends.


How many Internet backup connections can we have in NR+ mesh?


There is no limitation defined. The system deployment can decide how much redundancy they would like to have.


IPv6

How are IPv6 to radio device addresses resolved? In Ethernet we have the ARP table and in IPv6 we have neighbour discovery? What is implemented in DECT NR+?

In release 1, the gateway device needs to have an IPv6 to Long RD ID mapping table to map incoming IPv6 packets to Long RD ID. Currently, TC DECT is specifying an auto-configuration rule that enables generating IPv6 addresses from Long RD ID and vice-versa.

Effects of the Mesh

Would a mesh network structure require higher computing resource for devices acting as routers, compared with end-points in a star structure? It sounds like any device can be a node/router, which suggests high requirements for devices.

The design is such that the same HW and SW design can be used in both roles. This was demonstrated by Wirepas and Nordic Semiconductor during MWC 2023: Non-cellular 5G live at MWC.

How fast can mesh network forming and re-forming happen? For example: a cross-country running sports team?

Each radio device (RD) is evaluating the need for obtaining new routes as a constant process. Current use cases that have been considered have not introduced very high relative speed scenarios such as would be the case with cars or trains. Rather in the case of trains, there could be an IoT system in the train with a gateway moving at the same time, which would lean more practical deployment in many cases. However, in any case, if one RD was finding a new route to replace the old lost one, this would occur in seconds. The exact value would depend on a product design and configuration that can be matched to the use case.

In reality, in the case of a cross-country running team moving at between 3min to 6min per km (i.e., 20km/h), a better understanding of the use case would be needed in order to give a better estimation of how it would work.

Along with a possibility of adding a very large number of RDs to a DECT NR+ mesh, I am wondering if you have examples on the achieved maximum size of practical networks?

Both use cases that have been discussed during the technology development and the latest discussions in TC DECT indicate that practical deployments will reach city-wide networks. However, the technology itself does not introduce such limitations, rather it depends more on how the devices are deployed.

How is the discovery done when, for example, a leaf from one cluster would like to connect to another cluster and that cluster is working on a different frequency?

The leaf may learn about the other clusters in two different ways. The first method is scanning the network channel(s) and discovering network beacon messages transmitted by different clusters.

In the second method an RD device receives neighbouring cluster information directly from its own cluster’s RD FT in the neighbouring clusters information signalling that the RD FT has detected previously.

Does NR+ support mobility leafs moving from one cluster to another cluster?

Yes. 

Does NR+ support self-healing mesh?


Yes, this has been one of the main design objectives of DECT NR+.


Product related questions


What is the maximum range in the city and in an open field? How does that affect the power consumption?
 


The actual link distance is heavily dependent on the environment and how the devices are installed - such as the device’s height above the ground. Therefore, it is difficult to give exact values that can be generally applied. However, link distance measurements of around 2 km in an open field and around 300m in a city have been achieved by our industry.

Power consumption values are heavily product related and so it is impossible to give any generic values. Those you need to obtain directly from the chipset vendors. However, as a rule of thumb the receiver side power consumption is not link distance dependent. Transmitter side power consumption is dependent on link distance, as DECT NR+ uses power control to ensure optimum TX power, which can be between -40dBm to 23dBm.

When operating at a TX power of 10 dBm and below, the TX side power consumption becomes close to RX side power consumption, and when going towards 23dBm the TX power consumption starts to increase non-linearly due to power amplifier power consumption, which is implementation dependent. This suggests using short link distances to limit power consumption.

Do you know the actual power consumption of a routing device?

This is heavily product related. We recommend contacting Wirepas directly.

Are there any plans to develop an official DECT NR+ network simulator to help developers assess network performance during network design?

Several link and system simulation tools are available at both companies and various research organizations. However, those are their own internal assets. The DECT Forum has not taken action to initiate efforts for developing public simulator tools.

Routing


Is it possible to communicate from one PT device to another PT device without going over an FT device?

Yes, the technology supports local flooding between RDs.

Can an RD from Cluster2 route directly to Cluster6 without going through the Internet?


Yes, it is possible via local RD to RD flooding functionality whenever there is radio connectivity between clusters via one or multiple radio links.

Can the routing be tracked (is there any similar functionality to traceroute)?

No. Currently there is no functionality within DECT NR+ to track the route that a packet is travelling. There has been no use case for such functionality.

The basis of the technology is that a network is dynamic, and routes may be constantly changing to optimize communication routes and maintain reliability. Therefore, knowledge of the route over which a packet is being delivered has not been seen as useful in real system operations. 

Identification of the Network and Radio Device 


How is a global address formed, e.g. for addressing a device from outside of a network? For example, "networkId:lonDeviceId".

This is left for back-end implementation. However, when operating without an IPv6, the device can be addressed with Network ID and Long RD Id from external systems. When operating with IPv6, the device can be addressed with IPv6 from outside the DECT NR+ network.

Are RD IDs organized to manufacturers like Ethernet MACs?

No. A Long RD ID used in the network is given to the device when device is provisioned.  Release 1 assumes an external provisioning method, but in Release 2 TC DECT is standardizing means for RD authentication and provisioning methods over the DECT NR+ radio connectivity.  It is expected that with the  definitions done in Release 2 several authentication methods can be used, based on different application needs (industrial, utilities, building, healthcare, etc.).

Latency


Does Dect NR+ support ultra-low or low latency use cases?

Yes, this was evaluated in ETSI TR103 810. The low latency communication was studied both in single link and star network configuration. It was found that with IMT-2020 - i.e., 5G - latency and reliability requirements can be met with several different PHY configurations. Read more here:

https://www.etsi.org/standards#page=1&search=TR%20103%20810%20&title=0&etsiNumber=1&content=0&version=1&onApproval=0&published=1&withdrawn=1&historical=0&isCurrent=1&superseded=1&startDate=2021-05-01&endDate=2023-08-24&harmonized=0&keyword=&TB=&stdType=&frequency=&mandate=&collection=&sort=1

What is the minimum and typical latency?

This is highly dependent on the product, system configuration and system architecture used.

Latency values for the technology are given in ETSI TR103.810. 
https://www.etsi.org/standards#page=1&search=TR%20103%20810%20&title=0&etsiNumber=1&content=0&version=1&onApproval=0&published=1&withdrawn=1&historical=0&isCurrent=1&superseded=1&startDate=2021-05-01&endDate=2023-08-24&harmonized=0&keyword=&TB=&stdType=&frequency=&mandate=&collection=&sort=1

For a small amount of data, when transmitting with 1.728 MHz channel bandwidth, the latency is 416us, which equals one slot of the frame. A transmitter may dynamically increase the transmission length in terms of sub-slot time of 208us in 1.728 MHz operation, and as a result, air interface latency could be, for example, 1.25ms - but at the same time the amount of data is higher.  When operating with higher numerologies, e.g., subcarrier spacing of 54kHz or 108kHz ( = 2 or  = 4), the air interface latency is reduced by the same factor.

The second aspect impacting latency is the modulation and coding level used. DECT NR+ supports adaptive modulation and coding, which in practice means allowing to use higher data rate for link that provides reliable communication. This reduces the transmission time and mutual interference.

Are uplink and downlink messages equal in latency?

In a single link transmission, latency in both directions is the same. However, in Mesh communication, the design is up-link oriented for mMTC data and so latency is expected to be lower in UL, but the exact latency depends on the product and system deployment.

Security


Network IDs: Is it possible to harm another network, if, for example, someone intentionally uses the same network ID?

In the MAC security process, the radio device would discard all transmissions that fail integrity protection after the deciphering process, and so the impact would be minimal and local. If a DoS attack were to introduce a jammer on a radio channel, devices may locally select a new operating channel.

Related to DECT security, can the CVG security service be based on a device’s hardware secure element such as SIM (or eSIM/iSIM), or would it be SW-based?

The technology is open to both solutions.

Testing


Will a compliance testing specification be provided?

Yes, ETSI TC DECT has initiated Work Items for developing Technical Specifications for radio and protocol compliance and conformance testing. For the essential requirements for RED compliance ETSI has published EN 301 406-2.

Misc


Is there any advantage to using LoRa, and not DECT NR+, which is a 5G technology?

We think DECT NR+ is a very competitive technology that is also recognized by the ITU-R. We recommend that each company judge for themselves which technology is the best fit for their use cases.

Read the previous FAQ blogs:

Introduction to the DECT NR+ standard:

DECT NR+ audio applications:

DECT NR+ IoT applications:

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