Abstract not found

Existing works have approached the problem of reliable transport in ad-hoc networks by proposing mechanisms to improve TCP's performance over such networks. In this paper we show through detailed arguments and simulations that several of the design elements in TCP are fundamentally inappropriate for the unique characteristics of ad-hoc networks. Given that ad-hoc networks are typically stand-alone, we approach the problem of reliable transport from the perspective that it is justifiable to develop an entirely new transport protocol that is not a variant of TCP. Toward this end, we present a new reliable transport layer protocol for ad-hoc networks called ATP (ad-hoc transport protocol). We show through ns2 based simulations that ATP outperforms both default TCP and TCP-ELFN.

We present a link layer protocol called the Multi-radio Unification Protocol or MUP. On a single node, MUP coordinates the operation of multiple wireless network cards tuned to non-overlapping frequency channels. The goal of MUP is to optimize local spectrum usage via intelligent channel selection in a multihop wireless network. MUP works with standard-compliant IEEE 802.11 hardware, does not require changes to applications or higher-level protocols, and can be deployed incrementally. The primary usage scenario for MUP is a multihop community wireless mesh network, where cost of the radios and battery consumption are not limiting factors. We describe the design and implementation of MUP, and analyze its performance using both simulations and measurements based on our implementation. Our results show that under dynamic traffic patterns with realistic topologies, MUP significantly improves both TCP throughput and user perceived latency for realistic workloads. 1.

Abstract not found

Concurrent Multipath Transfer (CMT) uses the Stream Control Transmission Protocol’s (SCTP) multihoming

Abstract—Enabling video transport over ad hoc networks is more challenging than over other wireless networks. The wireless links in an ad hoc network are highly error prone and can go down frequently because of node mobility, interference, channel fading, and the lack of infrastructure. However, the mesh topology of ad hoc networks implies that it is possible to establish multiple paths between a source and a destination. Indeed, multipath transport provides an extra degree of freedom in designing error resilient video coding and transport schemes. In this paper, we propose to combine multistream coding with multipath transport, to show that, in addition to traditional error control techniques, path diversity provides an effective means to combat transmission error in ad hoc networks. The schemes that we have examined are: 1) feedback based reference picture selection; 2) layered coding with selective automatic repeat request; and 3) multiple description motion compensation coding. All these techniques are based on the motion compensated prediction technique found in modern video coding standards. We studied the performance of these three schemes via extensive simulations using both Markov channel models and OPNET Modeler. To further validate the viability and performance advantages of these schemes, we implemented an ad hoc multiple path video streaming testbed using notebook computers and IEEE 802.11b cards. The results show that great improvement in video quality can be achieved over the standard schemes with limited additional cost. Each of these three video coding/transport techniques is best suited for a particular environment, depending on the availability of a feedback channel, the end-to-end delay constraint, and the error characteristics of the paths. Index Terms—Ad hoc networks, error resilience, IEEE 802.11, multipath transport, video transport, wireless networks.

Wireless links have intrinsic characteristics that affect the performance of transport protocols; these include variable bandwidth, corruption, channel allocation delays, and asymmetry. In this paper we review simulation models for cellular, WLAN and satellite links used in the design of transport protocols, and consider the interplay between wireless links and transport. We argue that the design and evaluation of transport protocols can be improved by providing easily available models of wireless links that strike a balance between realism, generality, and detail.

Numerous transport protocols have been proposed in related work for use by mobile hosts over wireless environments. A common theme among the design of such protocols is that they specifically address the distinct characteristics of the last-hop wireless link, such as random wireless errors, round-trip time variations, blackouts, handoffs, etc. In this paper, we argue that due to the defining role played by the wireless link on a connection’s performance, locating the intelligence of a transport protocol at the mobile host that is adjacent to the wireless link can result in distinct performance advantages. To this end, we present a receiver-centric transport protocol called RCP (Reception Control Protocol) that is a TCP clone in its general behavior, but allows for better congestion control, loss recovery, and power management mechanisms compared to sender-centric approaches. More importantly, in the context of recent trends where mobile hosts are increasingly being equipped with multiple interfaces providing access to heterogeneous wireless networks, we show that a receiver-centric protocol such as RCP can enable a powerful and comprehensive transport layer solution for such multi-homed hosts. Specifically, we describe how RCP can be used to provide: (i) a scalable solution to support interface specific congestion control for a single active connection; (ii) seamless server migration capability during handoffs; and (iii) effective bandwidth aggregation when receiving data through multiple interfaces, either from one server, or from multiple replicated servers. We use both packet level simulations, and real Internet experiments to evaluate the proposed protocol.

Recent work on Internet measurement and overlay networks has shown that redundant paths are common between pairs of hosts and that one can often achieve better end-to-end performance by adaptively choosing an alternate path [8, 27]. In this paper, we propose an end-to-end transport layer protocol, mTCP, which can aggregate the available bandwidth of those redundant paths in parallel. By striping one flow’s packets across multiple paths, mTCP can not only obtain higher endto-end throughput but also be more robust under path failures. When some paths fail, mTCP can continue sending packets on other paths, and the recovery process normally takes only a few seconds. Because mTCP could obtain an unfair share of bandwidth under shared congestion, we integrate a shared congestion detection mechanism into our system. It allows us to dynamically detect and suppress paths with shared congestion so as to alleviate the aggressiveness problem. mTCP can also passively monitor the performance of several paths in parallel and discover better paths than the path provided by the underlying routing infrastructure. We also propose a heuristic to find disjoint paths between pairs of nodes using traceroute. We have implemented our system on top of overlay networks and evaluated it in both PlanetLab and Emulab. 1

Today the Internet offers a single path between end-systems even though it intrinsically has a large multiplicity of paths. This paper proposes an evolutionary architectural framework “BANANAS ” aimed at simplifying the introduction of multipath routing in the Internet. The framework starts with the observation that a path can be encoded as a short hash (“PathID”) of a sequence of globally known identifiers. The PathID therefore has global significance (unlike MPLS or ATM labels). This property allows multipath capable nodes to autonomously compute PathIDs in a partially upgraded network without requiring an explicit signaling protocol for path setup. We show that this framework allows the introduction of sophisticated explicit routing and multipath capabilities within the context of widely deployed connectionless routing protocols (e.g. OSPF, IS-IS, BGP) or overlay networks. We establish these characteristics through the development of PathID encoding and routecomputation schemes. The BANANAS framework also allows considerable flexibility in terms of architectural function placement and complexity management. To illustrate this feature, we develop an efficient variable-length hashing scheme that moves control-plane complexity and state overheads to network edges, allowing a very simple interior node design. All the schemes have been evaluated using both sizable SSFNet simulations and Linux/Zebra implementation evaluated on Utah’s Emulab testbed facility. 1.