Bundling of multiple access technologies is currently being standardized by 3GPP in the 5G access traffic steering, switching and splitting (ATSSS) framework, with the goal to increase robustness, resiliency and capacity of wireless access. A key part of an ATSSS framework is the packet scheduler, which decides the access network over which each packet is to be transmitted. As wireless channels are highly dynamic, a challenge for any scheduler is to correctly estimate the capacity of each path, and thereby avoid congesting the paths. In this paper, we further develop a recent packet scheduler that exploits cross-layer information from the congestion control state of individual transport layer tunnels when making scheduling decisions. Our aim is to achieve good path utilization while keeping the congestion delay low. Extensive emulations show that our approach reduces the excess delay at the bottleneck to as little as 34%. We furthermore show that our approach improves the performance of end-to-end applications including WebRTC and YouTube compared to state-of-the art. 

Multipath wireless access aims to seamlessly aggregate multiple access networks to increase data rates and decrease latency. It is currently being standardized through the ATSSS architectural framework as part of the fifth-generation (5G) cellular networks. However, facilitating efficient multi-access communication in next-generation wireless networks poses several challenges due to the complex interplay between congestion control (CC) and packet scheduling. Given that enhanced ATSSS steering functions for traffic splitting advocate the utilization of multi-access tunnels using congestion-controlled multipath network protocols between user equipment and a proxy, addressing the issue of nested CC becomes imperative. In this paper, we evaluate the impact of such nested congestion control loops on throughput over multi-access tunnels using the recently introduced Multipath DCCP (MP-DCCP) tunneling framework. We evaluate different combinations of endpoint and tunnel CC algorithms, including BBR, BBRv2, CUBIC, and NewReno. Using the Cheapest Path First scheduler, we quantify and analyze the impact of the following on the performance of tunnel-based multipath: (1) the location of the multi-access proxy relative to the user; (2) the bottleneck buffer size, and (3) the choice of the congestion control algorithms. Furthermore, our findings demonstrate the superior performance of BBRv2 as a tunnel CC algorithm.

Utilizing multiple access networks such as 5G, 4G, and Wi-Fi simultaneously can lead to increased robustness, resiliency, and capacity for mobile users. However, transparently implementing packet distribution over multiple paths within the core of the network faces multiple challenges including scalability to a large number of customers, low latency, and high-capacity packet processing requirements. In this paper, we offload congestion-aware multipath packet scheduling to a smartNIC. However, such hardware acceleration faces multiple challenges due to programming language and platform limitations. We implement different multipath schedulers in P4 with different complexity in order to cope with dynamically changing path capacities. Using testbed measurements, we show that our CMon scheduler, which monitors path congestion in the data plane and dynamically adjusts scheduling weights for the different paths based on path state information, can process more than 3.5 Mpps packets 25 μs latency.

5G will support transparent multi-path connectivity for mobile users through the Access Traffic Steering, Switching and Splitting function. For real-time traffic, this can be implemented by a multi-path proxy that implements transport layer tunnels between users and a proxy node in the packet core network. However, the choice of transport layer protocol for such a multi-path tunnel could greatly impact the user Quality-of-Experience. For example, re-transmitting lost packets could reduce video playback artefacts, but the additional delay caused by re-transmission could lead to the video freezing. In this paper, we develop mathematical models that estimate the lower bound on the average delay imposed by a reliable or semi-reliable multi-path tunnel. We validate our model using extensive network emulations and evaluate model accuracy for different scenarios. Finally, we use the model to derive design principles for a semi-reliable multipath tunnel protocol. 

Utilizing multiple access technologies such as 5G,4G, and Wi-Fi within a coherent framework is currentlystandardized by 3GPP within 5G ATSSS. Indeed, distributingpackets over multiple networks can lead to increased robustness,resiliency and capacity. A key part of such a framework isthe multi-access proxy, which transparently distributes packetsover multiple paths. As the proxy needs to serve thousands ofcustomers, scalability and performance are crucial for operatordeployments. In this paper, we leverage recent advancementsin data plane programming, implement a multi-access proxybased on the MP-DCCP tunneling approach in P4 and hardwareaccelerate it by deploying the pipeline on a smartNIC. Thisis challenging due to the complex scheduling and congestioncontrol operations involved. We present our pipeline and datastructures design for congestion control and packet schedulingstate management. Initial measurements in our testbed showthat packet latency is in the range of 25 μs demonstrating thefeasibility of our approach.

Networked systems have recently aimed to use multiple access networks in parallel to increase resiliency, availability and capacity. However, different paths may have different latency characteristics, which may lead to out-of-order packet delivery. This may severely impact both the end-to-end application performance and the capacity utilisation of multiaccess systems. In this paper, we show that in-network support for packet reordering for multiaccess systems that are based on multiple transport layer tunnels is beneficial for several application types. Our findings are applicable to TCP and QUIC traffic in the 3GPP ATSSS context, where we use the MP-DCCP tunneling framework with a buffer-based packet reordering approach that uses a dynamic timing threshold to cope with variation of path delays over time. We demonstrate achievable performance gains for a wide range of path latency differences and end-to-end round trip times when using different in-network reordering algorithms.

Bundling multiple access technologies increases capacity, resiliency and robustness of network connections. Multi-access is currently being standardized in the ATSSS framework in 3GPP, supporting different access bundling strategies. Within ATSSS, a multipath scheduler needs to decide which path to use for each user packet based on path characteristics. The Cheapest Path First (CPF) scheduler aims to utilize the cheapest path (e.g. WiFi) before sending packets over other paths (e.g. cellular). In this paper, we demonstrate that using CPF with an MP-DCCP tunnel may lead to sub-optimal performance. This is due to adverse interactions between the scheduler and end-to-end and tunnel congestion control. Hence, we design the Adaptive Cheapest Path First (ACPF) scheduler that limits queue buildup in the primary bottleneck and moves traffic to the secondary path earlier. We implement ACPF over both TCP and DCCP congestion controlled tunnels. Our evaluation shows that ACPF improves the average throughput over CPF between 24% to 86%.

In this paper we present the design and prototype implementation of a multi-domain congestion control framework based on a non-ossifying Lightweight Performance Enhancing Proxy. We demonstrate that our solution can be both used for evolved protocols such as end-to-end encrypted QUIC and for evolved cellular access networks like 5G. We also show the performance of our Multi-Domain Congestion Control algorithm by a simulation study. Moreover, we expose its behavior in realistic use cases like sudden capacity changes in 5G mmWave cellular networks. Our results highlight that significant performance improvements can be achieved by cooperative traffic management frameworks in protocols and networks of the future.

Mobile nodes are typically equipped with multiple radios and can connect to multiple radio access networks (e.g. WiFi, LTE and 5G). Consequently, it is important to design mechanisms that efficiently manage multiple network interfaces for aggregating the capacity, steering of traffic flows or switching flows among multiple interfaces. While such multi-access solutions have the potential to increase the overall traffic throughput and communication reliability, the variable latencies on different access links introduce packet delay variation which has negative effect on the application quality of service and user quality of experience. In this paper, we present a new IP-compatible multipath framework for heterogeneous access networks. The framework uses Multipath Datagram Congestion Control Protocol (MP-DCCP) - a set of extensions to regular DCCP - to enable a transport connection to operate across multiple access networks, simultaneously. We present the design of the new protocol framework and show simulation and experimental testbed results that (1) demonstrate the operation of the new framework, and (2) demonstrate the ability of our solution to manage significant packet delay variation caused by the asymmetry of network paths, by applying pluggable packet scheduling or reordering algorithms.

In order to increase the capacity of 5G networks, using mmWave band communication links both for access and backhaul are an important alternative due to the large spectrum portion available at those frequency bands. However, mmWave bands exhibit special propagation characteristics which require the usage of highly directional and beam-steerable antennas in order to cope with the significantly higher path loss. Using such links in urban scenarios may lead to frequent blocking events due to moving pedestrians or cars, which may result in the links dynamically changing their characteristics from Line-of-Sight (LOS) to Non Line-of- Sight (NLOS) or outage (OUT). Due to the immediate significant variation in available capacity when changing the link states, TCP connections may experience rapid spikes in end-to-end latency and severe bufferbloat may build up. Although bufferbloat solutions such as CoDel can be deployed to control the delay, they significantly impact capacity and fairness between different TCP flows sharing the same mmWave link. In this paper, we study this fairness issue when running multiple TCP connections over fluctuating mmWave links and deploying AQM schemes to control the latency. We study the effect of length and severity of the NLOS episode upon fairness and latency. Finally, we develop an algorithm that tunes the AQM parameters in order to increase fairness across flows having different RTTs while at the same time reduce their latency.