Multihop Wireless Networks

IEEE Network, 2000

Multicasting has emerged as one of the most focused areas in the field of networking. As the technology and popularity of the Internet grow, applications such as video conferencing that require the multicast feature a r e becoming more widespread. Another interesting recent development has been the emergence of dynamically reconfigurable wireless ad hoc networks to interconnect mobile users for applications ranging from disaster recovery to distributed collaborative comput. ing. In this article we describe the On-Demand Multicast Routing Protocol for mobile ad hoc networks. ODMRP is a mesh-based, rather than convention01 treebased, multicast scheme and uses a forwarding group concept [only a subset of nodes forwards the multicast packets via scoped flooding). It applies on-demand procedures to dynamically build routes and maintain multicast group membership. W e also describe our implementation of the protocol in a real laptop testbed. n ad hoc network [1, 21 is a dynamically reconfigurablc wirclcss network with no fixcd infrastructnre or central administration. Due to thc limitcd radio propagation rmgc of wireless deviccs, routcs are often multihop. Applications such as disastcr recovery, crowd control, scarch and rescue, and automated battlefields are typical examples of whcrc ad hoc networks iirc dcployed. Nodes in thesc nctworks move arbitrarily; thus, nctwork topology changes frequently and unprcdictably. Morcovcr, bandwidth and battery powcr arc limited. These constraints, io combination with the dynamic nctwork topology, tnakc routing and multicasting in ad hoc nctworks extremely chzillenging. In a lypical ad hoc cnvirnnmcnt, network hosts work in groups to carry out a givcn task. Hence, multicast plays an important role in ad hoc nctworks. Multicwt protocols used in static networksfor cxample, Distance Vcctor Multicast Routing Protocol (DVMKP) [3], Multicast Opcn Shortcst

2010

Wireless multihop communication is becoming more important due to the increasing popularity of wireless sensor networks, wireless mesh networks, and mobile social networks. They are distinguished from conventional multihop networks in terms of scale, traffic intensity and/or node density. Being readily-available in most of 802.11 radios, multirate facility appears to be useful to address some of these issues and is particularly helpful in high-density scenarios where inter-node distance is short, demanding a prudent multirate adaptation algorithm. However, communication at high bit rates mandates a large number of hops for a given node pair and thus, can easily be depreciated as per-hop overhead at several layers of network protocol is aggregated over the increased number of hops. This paper presents a novel multihop, multirate adaptation mechanism, called Multihop Transmission OPportunity (MTOP), that allows a frame to be forwarded a number of hops consecutively but reduces the MAC-layer overhead between hops. This seemingly collision-prone multihop forwarding is proven to be safe via analysis and USRP/GNU Radio-based experiment. The idea of MTOP is in clear contrast to, but not mutually exclusive with, the conventional opportunistic transmission mechanism, referred to as TXOP, where a node transmits multiple frames back-to-back when it gets an opportunity. We conducted an extensive simulation study via ns-2, demonstrating the performance advantage of MTOP under a wide range of network scenarios.

2013

Wireless communication has seen a tremendous growth in the last decades. Continuing on this trend, wireless multi-hop networks are nowadays used or planned for use in a multitude of contexts, spanning from Internet access at home to emergency situations. The Transmission Control Protocol (TCP) provides reliable and ordered delivery of a data and is used by major Internet applications such as web browsers, email clients and file transfer programs. TCP traffic is also the dominating traffic type on the Internet. However, TCP performs less than optimal in wireless multi-hop networks due to packet reordering, low link capacity, packet loss and variable delay. In this thesis, we develop novel proposals for enhancing the network and transport layer to improve TCP performance in wireless multi-hop networks. As initial studies, we experimentally evaluate the performance of different TCP variants, with and without mobile nodes. We further evaluate the impact of multi-path routing on TCP performance and propose packet aggregation combined with aggregation aware multi-path forwarding as a means to better utilize the available bandwidth. The last contribution is a novel extension to multi-path TCP to enable single-homed hosts to fully utilize the network capacity.

2012

Multi-hop wireless networks are the networks in which the communication is performed from one node to another using various intermediate nodes. Such networks are built using existing wireless protocols based on IEEE 802.11 and IEEE802.11e which are having various techniques to handle the congestion in the network. The basic idea of handling congestion is to use DROPTAIL protocol, which starts dropping packets as soon the as the networks starts congesting. This research focuses on the issue of handling congestion control by dropping packets, which leads to resend the packets again by the downstream nodes once the congestion is reduced. The process is more verse due to reproduction of packets at random times. In this paper, a new approach of controlling congestion is being proposed on the basis of a few more information maintained by nodes locally to slow down the network traffic inflow so that information shall not be gathered on a node and hence no need of dropping access packets in the network. The mechanism proposed is having various threshold values of the queue and flow rates decided in advance locally on each node and on occurrence of RTS (request to send) signal, CTS (clear to send) signal is sent back if and only if queue is not full or on the ratio of flow rates already decided.

Lecture Notes in Computer Science, 2003

Increasing popularity of wireless services has triggered the need for efficient wireless transport mechanisms. TCP, being the reliable transport level protocol widely used in wired network world, was not designed with heterogeneity in mind. The problem with the adaptation of TCP to the evolving wireless settings is because of the assumption that packet loss and unusual delays are mainly caused by congestion. TCP originally assumes that packet loss is very small. On the other hand, wireless links often suffer from high bit error rates and broken connectivity due to handoffs. A range of schemes, namely end-to-end, split-connection and link-layer protocols, has been proposed to improve the performance of transport mechanisms, in particular TCP, on wireless settings. In this study, we examine these mechanisms for wireless transport, and discuss our comparative simulation results of end-to-end TCP versions (Tahoe, Reno, NewReno and SACK) in various network settings including wireless LANs and wired-cum-wireless scenarios.

2011

Due to the high availability of cheap hardware, wireless multi-hop networks and in particular Wireless Mesh Networks (WMNs) are becoming popular in more and more contexts. For instance, IEEE 802.11 based WMNs have already started to be deployed as means to provide Internet access to rural areas in the developing world. To lower the cost and increase the coverage in such deployments, the wired network is extended with a wireless backbone of fixed mesh routers. With advances in technology and reduction in price comes also the possibility for more powerful wireless nodes, having multiple radios that allow transmitting on different channels in parallel. To be a successful platform for providing general Internet access, wireless multi-hop networks must provide support for common Internet applications. As most of the applications in the Internet today use the Transmission Control Protocol (TCP), TCP performance is crucial. Unfortunately, the design of TCP's congestion control that made it successful in today's Internet makes it perform less than optimal in wireless multi-hop networks. This is due to, among others, TCP's inability to distinguish wireless losses from congestion losses. The current trend for operating system designers is also to focus TCP development on high-speed fixed networks, rather than on wireless multi-hop networks. To enable wireless multi-hop networks as a successful platform there is therefore a need to provide good performance using TCP variants commonly deployed in the Internet. In this thesis, we develop novel proposals for the network layer in wireless multi-hop networks to support TCP traffic more efficiently. As an initial study, we experimentally evaluate different TCP variants, with and without mobile nodes, in a MANET context. Our results show that TCP Vegas, which does not provoke packet loss to determine available bandwidth, reduces the stress on the network while still providing the same or slightly increased performance, compared to TCP Newreno. We further propose and evaluate packet aggregation combined with aggregation aware multi-path forwarding to better utilize the available bandwidth. IP layer packet aggregation, where small packets are combined to larger ones before sent to the link layer, has been shown to improve the performance in wireless multihop networks for UDP and small packet transfers. Only few studies have been made on the impact of packet aggregation on TCP traffic, despite the fact that TCP traffic constitutes the majority of the Internet traffic. We propose a novel aggregation algorithm that is specifically addressing TCP relevant issues like packet reordering, fairness and TCP timeouts. In a typical WMN scenario, the aggregation algorithm increases TCP performance by up to 70 % and decreases round trip time (RTT) by up to 40 %. A detailed evaluation of packet aggregation in a multi radio setting has shown that a naive combination of multi path routing and packet aggregation can cause valuable aggregation opportunities to be lost. Therefore, we propose a novel combined packet aggregation and aggregation aware forwarding strategy that can reduce delay, packet loss and increase TCP performance by around 30 %.

ACM SIGCOMM Computer Communication Review, 2003

Existing wireless ad hoc routing protocols typically find routes with the minimum hop-count. This paper presents experimental evidence from two wireless test-beds which shows that there are usually multiple minimum hop-count paths, many of which have poor throughput. As a result, minimum-hop-count routing often chooses routes that have significantly less capacity than the best paths that exist in the network. Much of the reason for this is that many of the radio links between nodes have loss rates low enough that the routing protocol is willing to use them, but high enough that much of the capacity is consumed by retransmissions. These observations suggest that more attention be paid to link quality when choosing ad hoc routes; the paper presents measured link characteristics likely to be useful in devising a better path quality metric.

2010

Computer networks have long suffered from congestion. Congestion occurs when an increase in the offered load results in a decrease in the effective throughput of the network. The basic cause is that the short term packet arrival rate at some gateway exceeds its service rate. Existing congestion control schemes treat congestion as an individual problem and propose ad hoc solution that are dissatisfied. Wireless multi-hop networks have many potential applications, e.g., a small stand-alone network for group of mobile users (Mobile Ad Hoc Networks), a cost efficient stubnetwork to connect to the Internet (Wireless Mesh Networks), or a self-organized community network connecting houses together (Wireless Community Networks). We approach the problem from a different perspective: In this paper, we selected WXCP, CALC, WCP, WCCP congestion control protocols and conceptual study of DSR, AOMDV routing protocols for multi-hop networks. Subsequently we relax some of the assumptions and generalize the solution in terms of throughput and number of hops.

Network coding is a way of improving performance in wireless networks by combining two or more packets to send together as a single packet. Two or more packets are combined together to form a single packet. the main goal of using network coding is to reduce bandwidth requirement. Wireless networks often suffer from various issues like collision, transmission errors etc due to broadcasting of signals. Network coding helps in reducing such issues and improving performance significantly. Various network coding schemes are implemented at physical layer, data link layer and network layer. This research paper introduces a novel network coding scheme TCP-NC-TCP with Network Coding at transport layer. TCP's most widely deployed variant-TCP NewReno is used. Simulation is performed in NS 2.35. Scenario based wireless multihop networks are designed with different scenarios based on number of nodes, number of hopes and type of network(poor or congested). TCP-NC shows a significant amount of improvement when used with the poor network.

1999

In this study we investigate the interaction between TCP and MAC layer in a wireless multi-hop network. This type of network has traditionally found applications in the military (automated battlefield), law enforcement (search and rescue) and disaster recovery (flood, earthquake), where there is no fixed wired infrastructure. More recently, wireless "ad-hoc" multi-hop networks have been proposed for nomadic computing applications. Key requirements in all the above applications are reliable data transfer and congestion control, features that are generally supported by TCP. Unfortunately, TCP performs on wireless in a much less predictable way than on wired protocols.