Ultra-Reliable and Low-Latency Communications (URLLC) have been one of the new application scenarios for mobile communication systems in the fifth generation ecosystem ( 5G). In 5G radio environments, objective indicators have been defined, such as not exceeding 1ms of latency.

Before the arrival of 5G there was no real interest in improving the results of the double latency/reliability, beyond the experiences of critical communications as in the case of TETRA. Since 5G, it has already been focused on with a holistic approach, which affected not only wireless access to the medium, but also the core (core) of the network and the cloud architecture that services make use of.

The concept of latency is quite ambiguous in the industry. By end-to-end latency we understand the sum of a series of delays introduced by the design of the protocols and ‘environmental’ factors. The access time, queuing, packetizing, transmission, decoding, etc.

Something similar occurs with reliability, where it is also necessary to identify the different descriptions. Reliability per node is a sum of the probabilities of data transmission errors, queuing, packet loss, etc.

To achieve the combination of both characteristics, 5G has adopted a series of mechanisms such as packet duplication, multiconnectivity systems, slicing, densification, proposals based on diversity (MISA, network coding, etc.), throughput-delay tradeoffs, queue management , etc. These are what the industry has called key enablers. In the case of latency they have been:

Still, 5G URLLC is not enough for the latency or reliability requirements of some critical applications in the field of industrial automation (e.g. robot control), intelligent transportation, telemedicine, etc. such as use cases of virtual worlds or metaverse with the use of virtual reality (VR), etc.

In the 6G proposal, they are trying to achieve, in addition to the objective indicators defined in URLLC with 5G, others that allow enabling critical communications that have been left out. You’re talking about 9-nine reliability and sub-0.1 ms latency to support use cases like real-time human-machine interactions. That is why greater spectral efficiency, energy efficiency, performance (throughput), availability of services and network security are sought; as well as keeping the ‘Age of Information’ (AoI), jitter and round-trip delay low.

Meeting these new requirements is challenging as new design methodologies and innovative techniques are needed to bridge the technology gap between 5G URLLC and what the industry calls the future 6G xURLLC (from extended Ultra -Reliable and Low-Latency Communications). This type of technology is still in the research phase.

Managing latencies is the latest challenge in the world of unified communications. Both SIP and WebRTC are subject to performance improvements. They are technologies designed and relatively optimized for real-time communications, to the point that WebRTC is used, for example, in streaming scenarios (by reducing the usual latency of these services) but this does not prevent them from being subject to improvement possibilities.

There are initiatives for the reduction of headers or the elimination of message exchanges for user registration and call establishment, the improvement of media delivery management, the estimation of channels to maximize the user experience, etc. that allow reducing the delays generated and that complement the advances in the management of access to 5G and 6G networks.