End-to-end Focus for Low Latency in Wireless Networks

Posted by Marbenz Antonio on October 31, 2022

Breaking the Latency Barrier - IEEE Spectrum

Numbers for low latency are a dynamic goal. They are higher for low-throughput applications than they are for higher-throughput applications. In general, a proper network design affects latency. Along with end-to-end IP latency and the round-trip delay, radio latency must be taken into account. Wi-Fi, 5G, and Cisco Ultra-Reliable Wireless Backhaul (URWB) technologies all have one main factor that affects latency: the lower the possible latency, the closer applications are placed to where data is being processed in data centers, clouds, or at the network edge.

Applications Require Varied Speed Demands

Users are not affected by 150 milliseconds of latency in one direction when using VoIP, so it is acceptable. Sub-50 millisecond bi-directional response times are needed for augmented and virtual reality (AR/VR) and collaboration applications like WebEx or Microsoft Teams. Sub-20 ms response times in a high-throughput network are required for wirelessly operating an autonomous mobile robot (AMR) or an automated guided vehicle (AGV) in a factory, although some closed-loop process control traffic needs 10 ms or less end-to-end latency.

How to Calculate it Usually

End-to-end IP latency is typically measured from the wireless device to the IP transport network, wireless network, and application server. Bi-directional latency is calculated using round-trip time (RTT). The closer proximity of applications hosting the wireless devices makes achieving lower RTT latency possible.

The typical round-trip time (RTT) between an end user and a cloud provider or content distribution network (CDN) provider should be considered when assessing end-to-end IP performance. The time taken for data to traverse each network segment or component from the local device to its application needs to be estimated in network design aiming for a 150 ms RTT target. Data travels across both public and private IP infrastructure, including switches, routers, and firewalls, after a device connects to a local wireless network. This often leads to unpredictable delays before reaching the application over the Internet. Additionally, the processing time required before sending a response back must also be factored in when evaluating overall performance.

The Handling of Latency by Various Wireless Technologies

Every step of the radio hardware and uplink and downlink transmission processes is optimized in advanced 5G services like 5G Enhanced Mobile Broadband (eMBB) and 5G Ultra-Reliable Low Latency Communications (URLLC). According to whether spectral efficiency in eMBB or low latency in URLLC is the primary goal, new radio capabilities handle low latency communications by providing for a variable transmission time interval (TTI), which can scale from 1ms down to about 140 microseconds. The User Plane Function (UPF) in a 5G network receives IP packets from the radio through a tunnel and serves as the interface between the mobile infrastructure and the data network.

Despite operating in unlicensed bands, Wi-Fi is strictly regulated by countries. To minimize user interference, local rules define the maximum power levels for access points. Range, coverage, penetration, and signal strength are then determined by this. The Wi-Fi protocol’s determinism is expected to be increased in the upcoming generation, enabling better latency control in network architecture.

IP packets in a Wi-Fi network transit similarly from the access point to the wireless radio network, through tunnels to a wireless LAN controller, although Wi-Fi and 5G employ different kinds of encapsulations (WLC). A Wi-Fi WLC for the application server path should be designed as quickly as possible if low latency is needed for an application.

With Cisco Ultra-Reliable Wireless Backhaul (Cisco URWB), a wireless WAN backhaul technology developed from Wi-Fi and created to service mobile network settings, endpoints can move at high speeds with zero-delay handoffs thanks to the low-latency, extremely reliable, long-range connections (like vehicles, trains, or subways). While the end-to-end IP infrastructure, starting from the Cisco URWB gateway, shares similarities with Wi-Fi and 5G configurations and operates in unlicensed frequencies, the Cisco URWB segment necessitates a carefully designed setup to ensure rapid handover and minimal delay.

Recent changes send high-priority packets over redundant channels to maintain connectivity for fast-moving devices. Cisco’s Multipath Operations (MPO) technology, which is patented, can reduce interference and hardware failures by duplicating protected data up to 8 times, avoiding common paths, and working in conjunction with hardware availability for lower latency and improved availability.

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Depending on the application, low latency can mean different things and call for different solutions. Depending on the strategy and use cases of your company, the proper network design can lower latency to desired levels.

The round-trip delay and IP end-to-end latency must be taken into consideration while estimating radio latency. The closer applications are to the location where data is being processed, whether in a data center, cloud, or network edge, the lower the likely service latency. While many different factors contribute to reduced latency, using 5G, Wi-Fi, and Cisco URWB.

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