The Ad hoc On-Demand Distance Vector (AODV) routing protocol is intended for use by mobile nodes in an ad hoc network. It offers quick adaptation to dynamic link conditions, low processing and memory overhead, low network utilization, and determines unicast routes to destinations within the ad hoc network. It uses destination sequence numbers to ensure loop freedom at all times (even in the face of anomalous delivery of routing control messages), avoiding problems (such as "counting to infinity") associated with classical distance vector protocols.

/pdf/ad-hoc-on-demand-distance-vector-aodv-routing-2v7bybe614.pdf

Ad hoc On-Demand Distance Vector (AODV) Routing

The highly successful architecture and protocols of today's Internet may operate poorly in environments characterized by very long delay paths and frequent network partitions. These problems are exacerbated by end nodes with limited power or memory resources. Often deployed in mobile and extreme environments lacking continuous connectivity, many such networks have their own specialized protocols, and do not utilize IP. To achieve interoperability between them, we propose a network architecture and application interface structured around optionally-reliable asynchronous message forwarding, with limited expectations of end-to-end connectivity and node resources. The architecture operates as an overlay above the transport layers of the networks it interconnects, and provides key services such as in-network data storage and retransmission, interoperable naming, authenticated forwarding and a coarse-grained class of service.

/pdf/a-delay-tolerant-network-architecture-for-challenged-4nomv5ym6e.pdf

A delay-tolerant network architecture for challenged internets

The Transmission Control Protocol.

IP based solutions to accommodate mobile hosts within existing internetworks do not address the distinctive features of wireless mobile computing. IP-based transport protocols thus suffer from poor performance when a mobile host communicates with a host on the fixed network. This is caused by frequent disruptions in network layer connectivity due to i) mobility and ii) unreliable nature of the wireless link. We describe I-TCP, which is an indirect transport layer protocol for mobile hosts. I-TCP utilizes the resources of Mobility Support Routers (MSRs) to provide transport layer communication between mobile hosts and hosts on the fixed network. With I-TCP, the problems related to mobility and unreliability of wireless link are handled entirely within the wireless link; the TCP/IP software on the fixed hosts is not modified. Using I-TCP on our testbed, the throughput between a fixed host and a mobile host improved substantially in comparison to regular TCP.

/pdf/i-tcp-indirect-tcp-for-mobile-hosts-1jt85aeion.pdf

I-TCP: indirect TCP for mobile hosts

Theory and experiments show that as the per-flow product of bandwidth and latency increases, TCP becomes inefficient and prone to instability, regardless of the queuing scheme. This failing becomes increasingly important as the Internet evolves to incorporate very high-bandwidth optical links and more large-delay satellite links.To address this problem, we develop a novel approach to Internet congestion control that outperforms TCP in conventional environments, and remains efficient, fair, scalable, and stable as the bandwidth-delay product increases. This new eXplicit Control Protocol, XCP, generalizes the Explicit Congestion Notification proposal (ECN). In addition, XCP introduces the new concept of decoupling utilization control from fairness control. This allows a more flexible and analytically tractable protocol design and opens new avenues for service differentiation.Using a control theory framework, we model XCP and demonstrate it is stable and efficient regardless of the link capacity, the round trip delay, and the number of sources. Extensive packet-level simulations show that XCP outperforms TCP in both conventional and high bandwidth-delay environments. Further, XCP achieves fair bandwidth allocation, high utilization, small standing queue size, and near-zero packet drops, with both steady and highly varying traffic. Additionally, the new protocol does not maintain any per-flow state in routers and requires few CPU cycles per packet, which makes it implementable in high-speed routers.

/pdf/congestion-control-for-high-bandwidth-delay-product-networks-55e2v4vhlp.pdf

Congestion control for high bandwidth-delay product networks

In this paper we study the performance of TCP with a vertical handoff between access networks with widely varying link characteristics. TCP being an end-to-end protocol has performance problems as its behaviour depends on the end-to-end path properties which are likely to be affected by a vertical handoff. We propose a set of enhancements to the TCP sender algorithm that leverage on explicit cross-layer information regarding the changes in the access link delay and bandwidth. We carry out a systematic study to identify the problems of regular TCP and compare the performance of the regular TCP with the performance of the enhanced TCP algorithms in various handoff scenarios between access networks having different bandwidth and delay characteristics. Our experiments show that with cross-layer notifications TCP performance can be improved significantly in most vertical handoff scenarios.

https://www.cs.helsinki.fi/group/wiseciti/UH-IJCNDS.pdf

Employing cross-layer assisted TCP algorithms to improve TCP performance with vertical handoffs

Nomadicity is a new challenge for computing and communication technologies. Modern cellular telephone systems extend the usability of portable personal computers enormously. A nomadic user can be given ubiquitous access to remote information stores and computing services. However, the behaviour of wireless links creates severe inconveniences within the traditional data communication paradigm. In this paper we give an overview of the problems related to wireless mobility. We also present a new software architecture for mastering the problems and discuss a new paradigm for designing mobile distributed applications. The key idea in the architecture is to place a mediator, a distributed intelligent agent, between the mobile node and the wireline network.

Mobile access to the Internet: a mediator‐based solution

A bottleneck router typically resides close to the edge of the network where the aggregate traffic is often limited to a single or a few users only. With such limited aggregate traffic Random Early Detection (RED) on the bottleneck router is not able to properly respond to TCP slow start that causes rapid increase in load of the bottleneck. This results in falling back to tail-drop behavior or, at worst, triggers the RED maximum threshold cutter that drops all packets causing undesired break for all traffic that is passing through the bottleneck. We explain how TCP slow start, ACK clock and RED algorithm interact in such a situation, and propose Harsh RED (HRED) to properly address slow start in time. We perform a simulation study to compare HRED behavior to that of FIFO and RED with recommended parameters. We show that HRED avoids tail-drop and the maximum threshold cutter, has smaller queues, and provides less bursty drop distribution.

/pdf/harsh-red-improving-red-for-limited-aggregate-traffic-3gpk5kitrp.pdf

Harsh RED: Improving RED for Limited Aggregate Traffic

Internet of Things (IoT) seeks to broaden the scope of the Internet by connecting a variety of devices that can communicate with the Internet. Transport services for IoT are crucial in enabling the applications to communicate reliably and in a timely manner while making efficient and fair use of the potentially scarce network resources. The communication with IoT devices is often implemented using HyperText Transfer Protocol (HTTP) or a specifically designed protocol such as Constrained Application Protocol (CoAP) that is a specialized web transfer protocol for constrained nodes and networks. In this paper we discuss various options for modifying or adapting HTTP to offer better transport service for IoT environments. We consider HTTP, SPDY that has been developed to speed up HTTP in general, IoT-HTTP and IoT-SPDY that are adaptations of HTTP and SPDY for IoT, and CoAP as transport services for IoT and experimentally evaluate their performance. The results of our experiments show that CoAP has the lowest object download times and the least number of bytes transferred compared to the other four transport services. IoT-HTTP and IoT-SPDY have around 50% shorter object download times and smaller number of bytes transferred compared to HTTP and SPDY.

Experimental Evaluation of the CoAP, HTTP and SPDY Transport Services for Internet of Things

The Constrained Application Protocol (CoAP) has been designed to be used on constrained devices such as Internet of Things (IoT) devices. The existing congestion control algorithms for CoAP have known shortcomings in addressing congestion and retaining a good level of performance when link errors occur. In this paper, we propose Fast-Slow RTO (FASOR) mechanism that takes into account special needs in wireless environments while still properly addressing congestion. We run a series of experiments to confirm that FASOR is able to successfully cope with challenging network conditions such as bufferbloat, high level of congestion, and high link-error rates unlike the default and CoCoA congestion control that have severe problems with bufferbloated congestion.

/pdf/fasor-retransmission-timeout-and-congestion-control-2r4ro4zrp3.pdf

Markku Kojo

Papers

Employing cross-layer assisted TCP algorithms to improve TCP performance with vertical handoffs

Mobile access to the Internet: a mediator‐based solution

Harsh RED: Improving RED for Limited Aggregate Traffic

Experimental Evaluation of the CoAP, HTTP and SPDY Transport Services for Internet of Things

FASOR Retransmission Timeout and Congestion Control Mechanism for CoAP