Unicast Sessions Research Articles

Network coding construction for a special class of three unicast sessions

For a special class of three unicast sessions, in which the maximum flow from each sender to each receiver is the same positive integer k, a network coding approach is proposed. A multigeneration mixed strategy, in which (2 × n + 1) consecutive generations are taken as a mixed set, is adopted. The precoding strategy is adopted at the senders, random linear network coding technology is adopted at intermediate nodes to transmit data, and interference alignment technology is used at the receivers to eliminate some interference information. The proposed approach can construct a network coding data transmission scheme, in which the transmission rate vector of the senders is [(n + 1) × k/(2 × n + 1), n × k/(2 × n + 1), n × k/(2 × n + 1)]. The feasibility of the proposed approach is mathematically deduced and proven, and the simulation results verify the conclusions of the theoretical analysis.

Characterizing Resource Allocation Trade-Offs in 5G NR Serving Multicast and Unicast Traffic

The use of highly directional antenna radiation patterns for both the access point (AP) and the user equipment (UE) in the emerging millimeter-wave (mmWave)-based New Radio (NR) systems is inherently beneficial for unicast transmissions by providing an extension of the coverage range and eventually resulting in lower required NR AP densities. On the other hand, efficient resource utilization for serving multicast sessions demands narrower antenna directivities, which yields a trade-off between these two types of traffic that eventually affects the system deployment choices. In this work, with the tools from queuing theory and stochastic geometry, we develop an analytical framework capturing both the distance- and traffic-related aspects of the NR AP serving a mixture of multicast and unicast traffic. Our numerical results indicate that the service process of unicast sessions is severely compromised when (i) the fraction of unicast sessions is significant, (ii) the spatial session arrival intensity is high, or (iii) the service time of the multicast sessions is longer than that of the unicast sessions. To balance the multicast and unicast session drop probabilities, an explicit prioritization is required. Furthermore, for a given fraction of multicast sessions, lower antenna directivity at the NR AP characterized by a smaller NR AP inter-site distance (ISD) leads to a better performance in terms of multicast and unicast session drop probabilities. Aiming to increase the ISD, while also maintaining the drop probability at the target level, the serving of multicast sessions is possible over the unicast mechanisms, but it results in worse performance for the practical NR AP antenna configurations. However, this approach may become feasible as arrays with higher numbers of antenna elements begin to be available. Our developed mathematical framework can be employed to estimate the parameters of the NR AP when handling a mixture of multicast and unicast sessions as well as drive a lower bound on the density of the NR APs, which is needed to serve a certain mixture of multicast and unicast traffic types with their target performance requirements.

Network-Coded Cooperation and Multi-Connectivity for Massive Content Delivery

Massive content delivery is in the spotlight of the research community as both data traffic and the number of connected mobile devices are increasing at an incredibly fast pace. The enhanced mobile broadband (eMBB) is one of the main use cases for the fifth generation of mobile networks (5G), which focuses on transmitting greater amounts of data at higher data rates than in the previous generations, but also on increasing the area capacity (given in bits per second per square meter) and reliability. However, the broadcast and multicast implementation in 5G and presents several drawbacks such as unexpected disconnections and the lack of device-specific QoS guarantees. As a result, whenever the exact same content is to be delivered to numerous mobile devices simultaneously, this content must be replicated. Hence, the same number of parallel unicast sessions as users are needed. Therefore, novel systems that provide efficient massive content delivery and reduced energy consumption are needed. In this paper, we present a network-coded cooperation (NCC) protocol for efficient massive content delivery and the analytical model that describes its behavior. The NCC protocol combines the benefits of cooperative architectures known as mobile clouds (MCs) with Random Linear Network Coding (RLNC). Our results show the benefits of our NCC protocol when compared to the establishment of numerous parallel unicast sessions are threefold: offload data traffic from the cellular link, reduce the energy consumption at the cooperating users, and provide throughput gains when the cellular bandwidth is insufficient.

CMU-VP: Cooperative Multicast and Unicast With Viewport Prediction for VR Video Streaming in 5G H-CRAN

Virtual reality (VR) is commonly regarded as one of 5G killer-applications. Transmission efficiency and quality of experience (QoE) are the most concerning issues for VR video streaming in 5G networks. Several multicast approaches were proposed to address these issues regardless of variance of personal viewports. In this paper, we explore a novel scheme combining multicast and unicast sessions in heterogeneous cloud-radio access networks (H-CRAN), in which a basic version of the video is transmitted to all users through the g-NB in a multicast session, and tiles of enhanced-version are transmitted to each viewer in a unicast session through its stationed remote radio head (RHH). To ensure the real-time content delivery, a user's viewport is predicted using a method based on historical trajectories and similarity of motion behavior, and then the tiles of predicted viewport in a version dependent on the channel quality are sent to the user in the unicast session. The scheme is formulated into a mixed-integer nonlinear problem (MINLP), and two near-optimal solutions are proposed to solve it by applying greedy approach and approximate approach, respectively. The simulation results show that our proposed scheme ensures better QoE under constrained bandwidth, and the proposed near-optimal solutions can efficiently solve the problem with low complexity and comparable performance.

A Reduction Approach to the Multiple-Unicast Conjecture in Network Coding

The multiple-unicast conjecture in network coding states that for multiple unicast sessions in an undirected network, network coding has no advantage over routing in improving the throughput or saving bandwidth. In this paper, we propose a reduction method to study the multiple-unicast conjecture, and prove the conjecture for a new class of networks that are characterized by relations between cut-sets and source-receiver paths. This class subsumes all the known types of networks with non-zero max-flow min-cut gaps but zero coding advantage. Combining this result with a computer-aided search, we derive as a corollary that network coding is unnecessary in networks with up to six coding nodes. We also prove the multiple-unicast conjecture for almost all unit-link-length networks with up to three sessions and seven nodes.

Interest-suppression-based NDN live video broadcasting over wireless LAN

Named data networking (NDN) is a new Internet architecture that replaces today’s focus on where – addresses and hosts with what – the content that users and applications care about. One of NDN’s prominent advantages is scalable and efficient content distribution due to its native support of caching and multicast in the network. However, at the last hop to wireless users, often the WiFi link, current NDN implementation still treats the communication as multiple unicast sessions, which will cause duplicate packets and waste of bandwidth when multiple users request for the same popular content. WiFi’s built-in broadcast mechanism can alleviate this problem, but it suffers from packet loss since there is no MAC-layer acknowledgement as in unicast. In this paper, we develop a new NDN-based cross-layer approach called NLB for efficient and scalable live video streaming over wireless LAN. The core ideas are: using WiFi’s broadcast channel to deliver content from the access point to the users, a leader-based mechanism to suppress duplicate requests from users, and receiver-driven rate control and loss recovery. The design is implemented and evaluated in a physical testbed comprised of one software AP and 20 Raspberry Pi-based WiFi clients. While NDN with multiple unicast sessions or plain broadcast can support no more than ten concurrent viewers of a 1Mbps streaming video, NDN plus NLB supports all 20 viewers, and Received December 29, 2015; accepted April 28, 2016 E-mail: zhxp@tsinghua.edu.cn can likely support much more when present.

Inter-Session Network Coding Schemes for 1-to-2 Downlink Access-Point Networks With Sequential Hard Deadline Constraints

Next generation wireless networks will carry traffic from a wide range of applications, and many of them may require packets to be delivered before their respective deadlines. In this paper, we investigate using inter-session network coding to send packets wirelessly for two deadline-constrained unicast sessions. In particular, each unicast session aims to transmit a file, whose packets have hard sequential deadline constraints. We first characterize the corresponding deadline-constrained capacity region under heterogeneous channel conditions and heterogeneous deadline constraints. We show that this deadline-constrained capacity region can be achieved asymptotically by modifying the existing generation-based (G-B) schemes . However, despite its asymptotic optimality, the G-B scheme has very poor performance for small and medium file sizes. To address these problems, we develop a new immediately-decodable network coding (IDNC) scheme that empirically demonstrates much better performance for short file sizes, and we prove analytically its asymptotic optimality when used to send large files. Our analysis uses a novel version of drift analysis, which could also be of independent interest to other IDNC schemes.

An Efficient Fair Resource Allocation in Multicast Networks

A decentralized algorithm is presented that enables the different rate-adaptive receivers in different multicast sessions to adjust their rates to satisfy some fairness criterion. The problem of congestion control in networks, which supports both multirate multicast sessions and unicast sessions. A one-bit Explicit Congestion Notification (ECN) marking strategy to be used at the nodes is also proposed. The congestion control mechanism does not require any per-flow state information for unicast flows at the nodes. At the junction nodes of each multicast tree, some state information about the rates along the branches at the node may be required. This Paper calculates the throughput and rates of unicast and multicast packets for the given topology network receivers. The congestion control mechanism takes in to account the diverse user requirements when different receivers within a multicast session have different utility functions, but does not require the network to have any knowledge about the receiver utility functions. This paper compared the performance and fairness of unicast and multicast sessions.

A one-hop opportunistic network coding algorithm for wireless mesh networks

This paper proposes a Bearing Opportunistic Network (BON) coding procedure that operates in wireless multihop networks over multiple unicast sessions and it introduces very low overhead to the network. The BON coding is used to increase network performance in terms of a higher throughput and a lower delay. It can be seen as an independent layer in the communication stack, relying solely on information that is on the node itself. The proposed coding procedure is easy to implement and deploy. The performance evaluation of the BON coding procedure was performed in a dedicated simulation model. The comparison was made to the well-known network coding procedure COPE and the case where network coding is not used at all. Results show that BON coding increases the network goodput and decreases the delay in comparison to COPE and case where network coding is not used.

Inter-Session Network Coding-Based Policies for Delay Tolerant Mobile Social Networks

We consider delay tolerant mobile social networks (DTMSNs), which are opportunistic networks made of human-carried wireless devices clustered into social communities. In such environments, routing is a challenge as the limited resources (such as memory and contact opportunities) must be efficiently used and shared between the sessions (or users, contents). To handle several unicast sessions, inter-session network coding (ISNC) has been proved necessary for optimal throughput in general networks, but is a delicate problem as it can quickly get detrimental. This paper investigates that ISNC can be beneficial to DTMSNs when used on top of a social-aware routing algorithm, whereas we exemplify and make explicit why any gain can hardly be expected with greedy replication, in regard to the current literature on ISNC. We then design decentralized criteria to control when and where in the network ISNC should be triggered, based on the node features (buffer size and social relationships) and network current load. These criteria are tested extensively on real-world contact traces, in terms of various metrics, such as number of deliveries, mean delay, or fairness. Our online ISNC protocol builds on the SimBet utility-routing policy. Our ISNC protocol can, however, run on top of any social-aware routing.

INCP: Practical Wireless Network Coding for Multiple Unicast Sessions

In this paper, we propose INCP, inter-flow network coding protocol, for wireless mesh networks. INCP is designed with the concept of Layered Approach. It acts as a distinct layer above the MAC and has close cooperation with IP layer. INCP exploits the opportunities of network coding through multiple unicast sessions to decrease the number of transmissions, thereby increasing the aggregated throughput. Unlike most prior work that is mainly theoretical, INCP addresses the practical issues of network coding such as impact of lossy links, enabling/disabling RTS/CTS mechanism, packet size and its variation. We consider a retransmission mechanism to ensure a reliable broadcasting. We analyze the cost of this approach by providing a theoretical formulation for the amount of required bandwidth for successful broadcasting a coded packet to n neighbors. Further, we examine the coding gain for lossy networks by considering the ETX metric for routing in addition to traditionally shortest-path metric. The results, implemented in ns-3, show that not only INCP increases network throughput, but also improves the fairness of the IEEE 802.11 MAC. Moreover, the gain for real MAC is greater than the theoretical gain in most cases. The performance gain of INCP reaches up to several folds depending on the traffic model and congestion level.

Interflow Network Coding Approaches for Data Heterogeneous Unicast Sessions in Wireless Networks

The authors investigate the problem of reliable unicast transmissions in wireless ad hoc and WLAN/WiMAX networks. Currently, approaches using network coding show several-fold gain in terms of bandwidth efficiency over the traditional technique, “store and forward”. However, most of these approaches have assumed that all the information flows have the same packet size, while the others consider transmission flows with different size packets, then overcome the size-difference issue by padding more dummy data into the smaller size packets. In their approach, by exploiting the size differences of packets on different flows, the authors introduce a new technique at the relay node/access point/base station to improve network bandwidth efficiency. In particular, a symbol-adjusted technique has been proposed in creating coded packets to improve the reliability of transmissions. Both analytical and simulation results show that the proposed technique significantly improves the network performance over the current technique.

Joint Optimization of Rule Placement and Traffic Engineering for QoS Provisioning in Software Defined Network

Software-Defined Network (SDN) is a promising network paradigm that separates the control plane and data plane in the network. It has shown great advantages in simplifying network management such that new functions can be easily supported without physical access to the network switches. However, Ternary Content Addressable Memory (TCAM), as a critical hardware storing rules for high-speed packet processing in SDN-enabled devices, can be supplied to each device with very limited quantity because it is expensive and energy-consuming. To efficiently use TCAM resources, we propose a rule multiplexing scheme, in which the same set of rules deployed on each node apply to the whole flow of a session going through but towards different paths. Based on this scheme, we study the rule placement problem with the objective of minimizing rule space occupation for multiple unicast sessions under QoS constraints. We formulate the optimization problem jointly considering routing engineering and rule placement under both existing and our rule multiplexing schemes. Via an extensive review of the state-of-the-art work, to the best of our knowledge, we are the first to study the non-routing-rule placement problem. Finally, extensive simulations are conducted to show that our proposals significantly outperform existing solutions.

Adaptive Coding Optimization in Wireless Networks: Design and Implementation Aspects

A fundamental challenge in wireless networks is how to handle packet loss due to noise, interference, and dynamic channel effects, especially when there is no per-packet acknowledgement due to additional delay and potential loss of feedback packets. We design and implement a packet coding optimization scheme, applied at the source node, to enhance end-to-end transmission reliability in a lossy multi-hop network. Specifically, each source node transmits a file of packets to its destination node in the network where the end-to-end packet acknowledgement is not readily available because of the possible error or delay effects over multiple hops. By simply retransmitting packets, a source node cannot guarantee innovative packet arrivals at the destination node. Thus, we design an optimization scheme for adaptive packet coding applied at the source node to avoid transmitting redundant packets, thereby significantly improving the throughput, even for the case of a single unicast session. This scheme does not require any knowledge of network topology and can seamlessly operate with any routing or network coding protocol used at the intermediate relay nodes. We analyze the throughput properties of coded transmissions and verify the feasibility of performance gains via simulations. Then, we provide high fidelity emulation testbed results with real radio transmissions over emulated channels to evaluate the throughput gains. Without relying on end-to-end acknowledgment for each packet, we show that the adaptive packet coding optimization scheme can achieve significantly higher throughput than the retransmission scheme in lossy networks with unicast traffic.

Perfect Quantum Network Coding Independent of Classical Network Solutions

Quantum network coding with classical assistance can transmit quantum information with fidelity one in error-free quantum channels. However, the dependency on classical network solutions leads to higher communication complexity and transmission congestion over a large-scale network with bottleneck channels. We find that certain types of quantum operation are sufficient to support multiple unicast sessions over the extended butterfly network. Furthermore, this construction decouples classical communication (assisting decoding information) from classical network solution. Based on this design, we propose an optimal protocol for this specific network, which significantly reduces the communication cost.

Precoding-Based Network Alignment for Three Unicast Sessions

Author(s): Meng, C; Das, AK; Ramakrishnan, A; Jafar, SA; Markopoulou, A; Vishwanath, S | Abstract: We consider the problem of network coding across three unicast sessions over a directed acyclic graph, where the sender and receiver of each unicast session are both connected to the network via a single edge of unit capacity. We consider a network model in which the middle of the network can only perform random linear network coding, and restrict our approaches to precoding-based linear schemes, where the senders use precoding matrices to encode source symbols. We adapt a precoding-based interference alignment technique, originally developed for the wireless interference channel, to construct a precoding-based linear scheme, which we refer to as precoding-based network alignment scheme (PBNA). A primary difference between this setting and the wireless interference channel is that the network topology can introduce dependencies among the elements of the transfer matrix, which we refer to as coupling relations, and can potentially affect the achievable rate of PBNA. We identify all these coupling relations and interpret them in terms of network topology. We then present polynomial-time algorithms to check the presence of these coupling relations in a particular network. Finally, we show that, depending on the coupling relations present in the network, the optimal symmetric rate achieved by precoding-based linear scheme can take only three possible values, all of which can be achieved by PBNA.

A cross‐layer study for application‐aware multi‐hop cognitive radio networks

ABSTRACTSatisfying the different requirements of applications is important in multi‐hop cognitive radio networks, because the spectrum resources change dynamically and the requirements for various applications could be very different. In this paper, we propose new schemes of channel allocation and route selection for real‐time and non‐real‐time applications to tackle this challenge. Our scheme is flexible so that it can adapt to the different application requirements, and it can provide enough throughput while maintaining the packet loss rate and transmission rate requirements. First, we give the network model in a cognitive radio network environment, and show how to calculate the capacity of the route in multi‐hop cognitive radio networks. Second, we formulate optimization problems to fulfill the rate requirements of different applications for each unicast session. We also consider the primary user activities, channel availability, interface and interference constraint. We propose the corresponding routing and channel allocation schemes for different application scenarios. Third, we propose an admission control scheme to study the impact of application requirements for multiple sessions in cognitive radio networks. Finally, we implement simulations to show the performance of our schemes and compare them with existing schemes. Copyright © 2014 John Wiley & Sons, Ltd.

Towards a Fair and Efficient Packet Scheduling Scheme in Inter-Flow Network Coding

Network coding techniques are usually applied upon network-layer protocols to improve throughput in wireless networks. In scenarios with multiple unicast sessions, fairness is also an important factor. Therefore, a network coding-aware packet-scheduling algorithm is required. A packet-scheduling algorithm determines which packet to send next from a node’s packet backlog. Existing protocols mostly employ a basic round-robin scheduling algorithm to give “equal” opportunities to different packet flows. In fact, this “equal”-opportunity scheduling is neither fair, nor efficient. This paper intends to accentuate the importance of a coding-aware scheduling scheme. With a good scheduling scheme, we can gain more control over the per-flow throughput and fairness. Specifically, we first formulate a static scheduling problem and propose an algorithm to find the optimal scheduling scheme. We then extend the technique to a dynamic setting and, later, to practical routing protocols. Results show that the algorithm is comparatively scalable, and it can improve the throughput gain when the network is not severely saturated. The fairness among flows is drastically improved as a result of this scheduling scheme.

Maximum Throughput Gain of Compute-and-Forward for Multiple Unicast

Compute-and-Forward (CF), also known as reliable physical layer network coding, is a technique that provides the possibility of exploiting the features of broadcast and superposition in wireless networks. It has been shown that the throughput for multiple unicast traffic can be significantly boosted by CF. In this letter, the limit of such improvement is investigated by comparing the performance of CF with the traditional routing-based transmission schemes. For networks characterized by local interference and half-duplex constraints, it is proven that the throughput gain of CF over traditional routing, expressed by an improvement factor, is upper bounded by 3K, where K is the number of unicast sessions. Furthermore, a class of networks is presented for which an improvement by a factor of K/2 is feasible by applying CF. Hence, the throughput gain of CF is at most on the order of K for any network, and a gain in that order is indeed achievable for some networks.

Multipath Routing of Multiple Description Coded Images in Wireless Networks

Multiple description coding (MDC) generates multiple decodable bitstreams for a source to combat information loss. In this paper, multipath routing problem for two-description coded images is investigated for traditional and coded wireless networks without and with coding capability at intermediate nodes, respectively. Firstly, we formulate an interference-aware MDC multipath routing for traditional networks by employing a time-division link scheduling method to eliminate wireless interference, and ultimately obtain an optimal path selection corresponding to the minimum achievable distortion. Secondly, for coded networks, we evaluate practical wireless network coding (NC) in delivering descriptions of multiple unicast sessions. While NC increases maximum supporting flow rate of MDC descriptions in wireless networks, possible undecodability of NC mixed information is alleviated by MDC. To minimize achievable distortion, a proposed interference-and-coding-aware MDC multipath routing strikes a good balance between minimizing side effect of wireless interference avoidance and maximizing NC opportunity. Simulation results validate the effectiveness of the two proposed schemes.