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.

In modern multiservice networks, with terminals equipped with multiple network interfaces, there is a clear trend to move from the dominating single path transport towards multipath. There are obvious benefits of the multipath service delivery – these include better resilience and improved throughput – and the standardization of multipath transport protocols MP-TCP, MP-DCCP, MP-QUIC and their usage in the 3GPP rel. 16 5G ATSSS (Access Traffic Splitting, Steering and Switching) multipath framework pave the way for broad implementation. While the field of traffic distribution algorithms for multipath transport is subject of extensive research, this paper addresses the challenge of cost-based optimization of scheduling in the multipath 3GPP ATSSS context. The paper demonstrates that there is a major conflict for the Video-on-Demand (VoD) traffic between the achievable QoE and the consumed multipath resources when a simple path prioritization algorithm – e.g. the Cheapest-Path-First (CPF) – is used to direct traffic. Using real network and testbed trials, this paper shows that for VoD in multipath up to 90% of the expensive path resources are consumed while QoE does not take any advantage from this, primarily because of the natural burstiness of the VoD traffic. The paper then proposes a novel service transparent and lightweight Cost-Optimized-Multipath (COM) traffic scheduling algorithm. Using extensive measurement of YouTube video streams and a MP-TCP implementation of the COM scheduler, this work demonstrates that – by finding the right balance between the QoE and the incurred costs – the new scheduler can provide better QoE compared to the single path transport, while eliminating the spurious resource consumption on the expensive path.

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.

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.

This paper evaluates the limitations of existing scheduling algorithms when video-on-demand traffic is transported in multipath scenarios, and proposes a new scheduling algorithm called cost-optimized multipath (COM). The new algorithm is designed to decrease the mobile network operators' cost of the delivery of bursty video-on-demand traffic over multipath networks access. Local and Internet connected testbeds, as well as trials with real cellular customers have been deployed to analyse the video performance over MPTCP-based multipath. The results clearly demonstrate the impact the bursty nature of video-on-demand traffic has on the scheduling decisions in multipath scenarios, when traditional latency-based or cheapest-path-first schedulers are deployed. Based on the testbed and trial results, this paper presents the design of a new simple and scalable scheduling algorithm. The paper describes the typical use cases and shows preliminary testbed results, clearly demonstrating the cost benefits of the new algorithm, and indicating that the right balance between the user QoE and the operator cost can be achieved for the video traffic.

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%.

Providing multi-connectivity services is an important goal for next generation wireless networks, where multiple access networks are available and need to be integrated into a coherent solution that efficiently supports both reliable and non reliable traffic. Based on virtual network interfaces and per path congestion controlled tunnels, the MP-DCCP based multiaccess aggregation framework presents a novel solution that flexibly supports different path schedulers and congestion control algorithms as well as reordering modules. The framework has been implemented within the Linux kernel space and has been tested over different prototypes. Experimental results have shown that the overall performance strongly depends upon the congestion control algorithm used on the individual DCCP tunnels, denoted as CCID. In this paper, we present an implementation of the BBR (Bottleneck Bandwidth Round Trip propagation time) congestion control algorithm for DCCP in the Linux kernel. We show how BBR is integrated into the MP-DCCP multi-access framework and evaluate its performance over both single and multi-path environments. Our evaluation results show that BBR improves the performance compared to CCID2 (TCPlike Congestion Control) for multi-path scenarios due to the faster response to changes in the available bandwidth, which reduces latency and increases performance, especially for unreliable traffic. The MP-DCCP framework code, including the new CCID5 is available as OpenSource1.

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.

Over the past decade, the way that devices connect to the Internet has changed drastically. The introduction of high-speed mobile networks and the omnipresence of wireless access points led to a situation where most devices offer multiple network interfaces, such as cellular and WiFi radios. However the most prevalent Layer 4 protocol, TCP, is not multipath capable and thus limited to using one interface at a time [4]. Multipath TCP [6], which is based on the classic TCP, resolves this problem by spreading the data flow across multiple paths. When a new connection is established, an initial subflow is created for backwards compatibility to TCP; afterwards, additional subflows can be created and MPTCP offers resilience against link failures [1]. Depending on the first flow to create a new connection prevents MPTCP from exploiting multi-link capabilities during the establishment phase. Therefore, if the initial subflow is not successful, a connection cannot be established. In this paper an extension to the existing MPTCP standard is proposed: MPTCP RobE. This solution extends the inherent resiliency of MPTCP against link failures to the establishment phase by introducing the concept of several potentially initial subflows, which tremendously increases the chance to build a successful initial subflow, and at the same time improves end-to-end latency during the establishment phase significantly. In this paper, three different concepts for MPTCP RobE are proposed and discussed with regard to technical aspects and MPTCP standard integration. Finally, a protoype is used to verify the performance of MPTCP RobE with respect to robustness and latency gains in different scenarios.

Bundling the resources of different access links is a measure to improve throughput and resilience to network failure. This paper proposes a solution able to bundle the own DSL resources with available resources of neighbouring DSLs. The solution is based on links between the DSL routers (e.g. using Wi-Fi technology) which are used by the bundling algorithm to distribute data packets over the available DSLs. The proposed solution has been implemented in a testbed in order to investigate possible bundling gains under realistic conditions. This paper presents details about the solution itself as well as the implementation and the testbed. Intensive performance measurements based on a testbed are discussed. Results show that high bundling gains can be achieved. Results also show that the link between the DSL routers is the most critical part which needs to be configured and dimensioned with care.

Residential access networks of internet service providers have evolved from copper-based public switched telephone networks to digital broadband access networks now based on a mixture of copper and fibre infrastructure components. It is generally well accepted that an FTTH-network (Fibre-to-the-Home), where the fibre runs all the way to the customer

The Datagram Congestion Control Protocol (DCCP) is a transport-layer protocol that provides upper layers with the ability to use non- reliable congestion-controlled flows. DCCP is not widely deployed in the Internet, and the reason for that can be defined as a typical example of a chicken-egg problem. Even if an application developer decided to use DCCP, the middle-boxes like firewalls and NATs would prevent DCCP end-to-end since they lack support for DCCP. Moreover, as long as the protocol penetration of DCCP does not increase, the middle-boxes will not handle DCCP properly. To overcome this challenge, NAT/NATP traversal and UDP encapsulation for DCCP is already defined. However, the former requires special middle-box support and the latter introduces overhead. The recent proposal of a multipath extension for DCCP further underlines the challenge of efficient middle-box passing as its main goal is to be applied over the Internet, traversing numerous uncontrolled middle-boxes. This document introduces a new solution which disguises DCCP during transmission as UDP without requiring middle-box modification or introducing any overhead.

This document briefly presents the Access Traffic Steering, Switching,and Splitting (ATSSS) service being specified within the 3rdGeneration Partnership Project (3GPP). The ATSSS service providesnetwork support for multihomed devices to select a path fortransmission (steer), move traffic from one path to another (switch),or use multiple paths simultaneously (split). TS 23.501 specifies anATSSS architecture for TCP traffic. This document presents a snap-shot of the ongoing discussion in the 3GPP to enable ATSSS for non-TCPtraffic, based on the use of QUIC, and assesses to what extent IETFspecifications can be used to meet the ATSSS design goals. Apparentgaps are also documented.

DCCP communication is currently restricted to a single path perconnection, yet multiple paths often exist between peers. Thesimultaneous use of these multiple paths for a DCCP session couldimprove resource usage within the network and, thus, improve userexperience through higher throughput and improved resilience tonetwork failure. Multipath DCCP provides the ability tosimultaneously use multiple paths between peers. This documentpresents a set of extensions to traditional DCCP to support multipathoperation. The protocol offers the same type of service toapplications as DCCP and it provides the components necessary toestablish and use multiple DCCP flows across potentially disjointpaths.

More and more of today's devices are multi-homing capable, in particular 3GPP user equipment like smartphones. In the current standardization of the next upcoming mobile network generation 5G Rel.16, this is especially targeted in the study group Access Traffic Steering Switching Splitting [TR23.793]. ATSSS describes the flexible selection or combination of 3GPP untrusted access like Wi-Fi and cellular access, overcoming the single-access limitation of today's devices and services. Another multi-connectivity scenario is the Hybrid Access [I-D.lhwxz-hybrid-access-network-architecture][I-D. muley-network-based-bonding-hybrid-access], providing multiple access for CPEs, which extends the traditional way of single access connectivity at home to dual-connectivity over 3GPP and fixed access. A missing piece in the ATSSS and Hybrid Access is the access and path measurement, which is required for efficient and beneficial traffic steering decisions. This becomes particularly important in heterogeneous access networks with a multitude of volatile access paths. While MP-TCP has been proposed to be used within ATSSS, there are drawbacks when being used to encapsulate unreliable traffic as it blindly retransmits each lost frame leading to excessive delay and potential head-of-line blocking. A decision for MP-TCP though leaves the increasing share of UDP in today's traffic mix ( ) unconsidered. In this document, a multi-access framework is proposed leveraging the MP-DCCP network protocol, which enables flexible traffic steering, switching and splitting also for unreliable traffic. A benefit is the support for pluggable congestion control which enables our framework to be used either independent or complementary to MP-TCP.