5G promises many things to many people. One of these promises is to provide near-zero latency with high reliability for mission-critical applications. The industry calls this ultra-reliable low latency communication (URLLC). It has potential use cases in factory automation, autonomous driving, smart grids, virtual reality and haptic systems (e.g. giving a sense of touch to a surgeon operating remotely).
Many things contribute to a data packet’s latency as it travels from a user’s device across a network to its destination. IP routers are one of the elements along this pathway, and they have an important role to play in latency.
Latency includes processing at the user equipment (UE), application processing performed in the cloud, and transport in both directions between the UE and the cloud.
The following table shows average LTE and 3G latency in milliseconds for selected countries, according to recent OpenSignal reports.
|Country||LTE latency (ms)||3G latency (ms)|
LTE latency is roughly half of 3G latency but there is work to do to achieve the target 1–10 milliseconds required for 5G URLLC applications. Industry experts are finding solutions for reducing latency at each step along the pathway, notably on the radio portion. Mobile transport, or anyhaul, as we like to call it, accounts for a portion of the latency. The size of this portion depends on distance, geography and network architecture. IP routing is part of the anyhaul network, so let’s take a closer look at the role it plays in latency.
Latency across a router is measured as the time from when the first bit arrives at the router until the last bit leaves the router. For routers in today’s networks, this is in the tens of microseconds. Latency of a few microseconds may seem negligible, but as I learned the hard way in backpacking, where every gram counts - the goal is to take latency below 10 millisecond, so every microsecond matters.
New routers coming to market in 2018 with the latest generation of silicon are reaching latency speeds of under 10 microseconds. But congestion affects latency, so these speeds may be more difficult to achieve in periods of high traffic. It’s like saying the commute to work takes 15 minutes at midnight, when we know it can take an hour in rush hour. Applications that require low latency need to have the right level of service so that they can be given priority and transported straight through the router without buffering. Delay variation (also called jitter) is also a critical concern. It must be minimized.
Ultra-reliability goes hand in hand with low latency for 5G mission-critical applications. To guarantee service levels, routers need redundancy, fast convergence times based on the best possible control-plane performance, and in-depth, per-service packet flow monitoring.
Operators seeking to upgrade their transport networks for 5G should look beyond throughput and port counts and consider IP router latency, quality of service and reliability features. These features present a tremendous opportunity to create new services and generate new revenues while meeting the needs of 5G-era applications.
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