Kubernetes (K8s) has become the cornerstone solution for orchestrating containerized applications across cloud-edge computing environments. Container Network Interface (CNI) plugins are crucial in this ecosystem, enabling network connectivity among K8s components, supporting advanced features and facilitating robust network management across diverse environments, such as centralized cloud or decentralized edge locations. In this paper, we extend our previous work, focusing on the various features, either built-in or non-native, provided within each networking solution and across diverse resource-intense and lightweight K8s distributions. Along these lines, tunneling options, security and encryption mechanisms, as well as common service mesh and observability tools have been evaluated with regards to their performance and resource utilization.

Kubernetes (K8s) serves as a mature orchestration system for the seamless deployment and management of containerized applications spanning across cloud and edge environments. In this context, optimizing Kubernetes networking to achieve high-performance connectivity and minimal resource utilization is crucial for its applicability and effectiveness at the edge. This paper contributes to this effort, by conducting a qualitative and quantitative performance evaluation of diverse Container Network Interface (CNI) plugins within different K8s environments, incorporating lightweight implementations designed for the Edge. Our experimental assessment was conducted in two distinct (intra- and inter-host) scenarios, revealing interesting insights and tradeoffs for both researchers and practitioners. For example, the deployment of plugins across lightweight distributions does not necessarily lead to resource utilization improvements, e.g., in terms of CPU/memory or throughput, while, in contrast, their impact on lifecycle metrics such as pod readiness times, is significant.

Smart cities are progressively emerging and require city-wide networks able to maintain low delay and increased reliability. However, wireless communications in the urban environment are occasionally disrupted, leading to volatile network conditions and impeding traditional networks to cope with these demands. To this end, Named Data Networking (NDN) and Delay/Disruption Tolerant Networking (DTN) architectures, as well as the combined NDN-over-DTN (NoD) scheme have been introduced and are actively investigated for combating distinct communication challenges in wireless city-wide deployments. In this work we investigate the performance and reliability trade-offs of each approach in the smart city context, and accordingly propose an experimental system that employs interchangeably NDN, DTN and NoD driven by a novel Change Point (CP) based network reliability detector. The real-world experiments showed that the proposed multi-protocol adaptive system, called ALTER, leads to lower latency and increased reliability of the urban network, compared to non-adaptive NDN and NoD solutions.

Internet of Things (IoT) evolution transformed modern cities into smart cities. As smart cities are becoming part of our everyday lives, it becomes essential to address challenging communication issues that are present, such as the intermittent connectivity, the link asymmetry and the indirect line-of-sight. In this work we propose an adaptive solution that employs interchangeably Named-Data Networking (NDN), Delay/Disruption-Tolerant Networking (DTN) and NDN-over-DTN (NoD) to compensate reliability issues and enable the seamless smart city network operation using the Software-Defined Networking (SDN) technology. The implemented system has been deployed and validated in the CityLab test-bed, a real smart city network located in Antwerp, Belgium. The evaluation results show that our adaptive protocol solution outperformed the single NoD scheme in terms of Content Retrieval Delay, Interest Satisfaction Ratio and Cache Hit Ratio.

The Internet of Things (IoT) requires bespoke proto-cols due to the resource constraints and susceptibility to malfunctions, plaguing IoT devices. The Named Data Networking (NDN) paradigm is well-suited to meet the particular IoT requirements thanks to its native in-network caching feature that facilitates asynchronous data sharing and consumption and provides native mobility support. In this paper, we propose the ‘Energy-aware and Fault-tolerant Probabilistic Caching’ (EFPCaching) policy, which incorporates energy consumption and sensor faults in caching decisions. Introducing fault awareness in caching constitutes the novelty of our approach. We compared the performance of our strategy against state-of-the-art caching policies, and the evaluation results demonstrate that EFPCaching has distinct benefits in terms of cache and energy efficiency.

Information-Centric Networking (ICN) has emerged as a perfect match to support data-driven applications. Typically, ICN ensures data integrity and authenticity, by provisioning signed and verifiable data packets. Nonetheless, the ICN cryptography-based security scheme entails increased computational and communication cost, while also necessitates continuous connectivity to the infrastructure. We claim that this security approach requires supportive mechanisms to perform adequately in scenarios involving disruptive connectivity and short-term communication. In this paper, we investigate the applicability of two security approaches, namely the in-force cryptographybased approach and a ‘lighter’ reputation-based one, in ad hoc information-centric networks, and aim to identify the pros and cons of each solution. Our experiments rely on a scenario deemed appropriate for the particular research objective: we selected an ICN-based Flying Ad hoc Network (FANET). We assess the impact of intermittent connectivity, as well as, the associated computational and communication cost, and the dynamics of mobility. Our results demonstrate that the reputation-based approach allows for building trust relations in a fast and lightweight manner, but without requiring permanent connectivity to trusted third parties. Therefore, we argue that the standard ICN security system can be consolidated by integrating reputation-based trust as an essential complementary mechanism.

We propose an SDN-based Non-IP multi-protocol platform (REWIRE) that mixes and matches, on-demand, multi-ple Non-IP protocol strategies with real rapidly-detected network conditions and loT data communication patterns. The REWIRE solution supports centralized monitoring of Wireless Mesh Net-works (WMN) and manages alternative Non-IP protocols stacks (i.e., NDN, DTN & NoD) in an adaptable manner based on change-point analysis & clustering mechanisms. To this end, our proposal grafts flexibility and adaptability capabilities to the WMN providing the communication backbone in real Smart-City environments. Our platform was implemented in real WMNs environments over Fed4FIRE+ test-beds considering an loT sce-nario using traffic patterns based on real sensor measurements.

Named Data Networking (NDN) has emerged as a promising Future Internet architecture. NDN provisions security by design and guarantees that data packets are immutable and authentic. Nevertheless, its inherent in-network caching feature has opened the door to new types of security attacks. One such critical security issue in NDN is content poisoning attacks. In content poisoning, the attacker aims at injecting poisonous (i.e., fake or invalid) content in the network caches. In this paper, we propose a reputation-based content poisoning mitigation model, which assists both the access and the core network nodes in identifying the sources from which poisonous content is originated, and subsequently, limiting the Interest flow towards those notorious sources as well as in avoiding caching poisonous content.

The Named Data Networking and Delay Tolerant Networking architectures were originally targeting distinct networking domains: NDN was designed for content retrieval within fixed networks, while DTN was aiming to deliver data in highly-dynamic wireless topologies with intermittent connectivity. In this paper, we argue that the two technologies can complement each other to shape a joint NDN-DTN scheme which can improve data retrieval from intermittently-connected devices, such as IoT and sensor networks in remote areas. We quantify the improvements by using both DTN- and NDN- associated metrics combined in a common analytical framework and show that NDN-DTN can greatly improve the Interest Satisfaction Ratio and Average Delay when compared to a DTN-only approach, especially in environments with a low Delivery Ratio. We verify our results through experiments with intermittently-connected IoT devices and investigate the impact of parameters such as Interest Lifetime, Data Freshness Period and Contact Duration. We conclude that a joint NDN-DTN approach outperforms a legacy DTN -only setup.

Summary form only given, as follows. The complete presentation was not made available for publication as part of the conference proceedings. Space flight and Internet service are technologies that are currently complementary but seem to be on the verge of integration into a new ”space internetworking” discipline. I will claim that a comprehensive realization of space internetworking technology should provide an infrastructure for universal interconnection among humans and their artifacts and could dramatically enhance space exploration, augment terrestrial industry and commerce, benefit the economically disadvantaged, and nurture human and civil rights. Part of the talk will be based on joint work with Scott Burleigh, Vint Cerf and Jon Crowcroft.

The continuous increase of Internet users worldwide, as well as the extensive need to support real-time traffic and bulk data transfers simultaneously, has directed research towards service differentiation schemes. These schemes either propose techniques that provide users with the necessary quality guarantees or follow a "better-than-best-effort" approach to satisfy broadly the varying needs of different applications. We depart from our new service principle called Less Impact Better Service (LIBS) and propose a novel service differentiation method, namely size-oriented dropping policies, which uses packet size to categorize time-sensitive from delay-tolerant flows and prioritize packet dropping probability, accordingly. Unlike existing proposals, the distinction of flows is dynamic and the notion of packet size is abstract and comparative; a packet size is judged as a unit within a dynamic sample space, that is, current queue occupancy. We evaluate size-oriented dropping policies both analytically and experimentally; we observe a significant increase on the perceived quality of real-time applications. Delaysensitive flows increase their bandwidth share, to reach a state of system fairness, regulating the dominant behavior of bulk-data flows.

We discuss a new packet service paradigm, called "Less Impact Better Servicerdquo (LIBS), which is realized through a novel queuing discipline, called "noncongestive queuingrdquo (NCQ). NCQ prioritizes small packets when conditions permit and utilizes service thresholds to confine the delay impact of prioritization on congestive applications. We show that LIBS and NCQ satisfy more users with diverse demands on delay and throughput. We obtained both analytical and simulation results, which are very promising. Diversity is simulated by using FTP, sensor, and VoIP traffic.

In this paper, we propose a new streaming protocol, namely dynamic video rate control (DVRC), which enables adaptive video delivery over the Internet. DVRC operates on top of HDP providing a congestion-controlled flow of unreliable datagrams. The proposed rate control scheme is able to interact with new and existing video streaming applications which are capable of adjusting their rate based on congestion feedback. DVRC attempts to optimize the performance of video delivery with concern to friendliness with interfering traffic. Exploring DVRC's potential through extensive simulations, we identify notable gains in terms of bandwidth utilization and smooth video delivery. Furthermore, our results indicate that the protocol allocates a well-balanced amount of network resources maintaining friendliness with coexisting flows.

Window-based congestion control is typically based on exhausting bandwidth capacity, which occasionally leads to transient congestion. Moreover, flow synchronization may deteriorate conditions further, leading to persistent or more severe congestion, which is experienced by flows through increasing queuing delays and packet retransmission. Head-to-Tail is a new approach to queue scheduling that aspires to alleviate this problem. When conditions at the router's buffer indicate high risk for congestion, Head-to-Tail delays packets intentionally to fabricate the senders' impression about the network load. This implicit signal to reduce the transmission rate allows for a responsive behavior prior to congestion. In this paper, we evaluated Head-to-Tail with TCP Vegas and compared it with RED and other TCP variants. The initial results indicate that congestion events and retransmissions can be significantly eliminated.

Media-streaming applications experience limited performance and perceptible quality degradation in the presence of random wireless errors, as the underlying congestion control typically interprets packet loss as the outcome of congestion. In this context, we propose a selective rate control, namely AIAMD, which manages to differentiate congestive and non-congestive loss by utilizing history in its control rules. AIAMD combines the most desirable features of additive increase additive decrease (AIAD) and additive increase multiplicative decrease (AIMD) controls, reacting gently to wireless loss and more aggressively to congestion. Exploring AIAMD's potential, we identify notable gains in terms of link utilization and media delivery, without compromising intra-protocol fairness.

We evaluate selected research proposals towards the efficient real-time QoS management over wireless links. We mainly focus on real-time performance of link-and transport-level mechanisms that bind operationally wired and wireless links. Employing a new metric for the evaluation of real-time performance we demonstrate that there are occasions where increased goodput does not correspond to real-time performance gains. In the sequel, we exploit further the potential of transport layer approaches

In this paper, we propose a new transport protocol, namely scalable streaming video protocol (SSVP), which employs an AIMD-oriented congestion control mechanism. SSVP, in a complementary role, operates on top of UDP and is specifically designed to support unicast video streaming applications. The transmission rate is controlled by properly adjusting the inter- packet-gap, spacing outgoing packets evenly to produce a smoothed flow. SSVP attempts to optimize the performance of streaming video delivery with concern to friendliness with interfering traffic. Quantifying SSVP's performance, we identify that the protocol utilizes a higher fraction of the available bandwidth, and maintains a regular transmission rate with oscillations of a smaller magnitude in comparison with existing congestion control schemes.

We present a new timeout algorithm for TCP, based on the observation that TCP-RTO should not be solely based on RTT estimations. We argue that the design principles of the current timeout algorithm may lead to flow synchronization, unnecessary retransmission effort and unfair resource allocation. WB-RTO exhibits two major properties: (i) it cancels retransmission synchronization which dominates when resource demand exceeds by far resource supply and (ii) reschedules flows on the basis of their contribution to congestion.

We study transport protocol performance from an application-specific perspective. Initially, we focus on TCP and UDP supportive role in the context of VoIP performance. Applying our metric for real-time performance, we discover that UDP has limited efficiency. Beyond UDP/TCP, we evaluate a solution-framework based on TCP protocols which incorporate variable congestion mechanisms. We also investigate VoIP traffic friendliness, as well as potential tradeoffs between protocol performance and fairness. Furthermore, we evaluate VoIP quality and protocol sensitivity versus a range of QoS parameter adjustments.

We investigate the energy-saving potential of transport protocols. We seek an answer to strategic issues of maximizing energy and bandwidth exploitation, without damaging the dynamics of multiple-flow equilibrium. We claim that (i) an energy-saving strategy of the transport level needs to be associated with some energy potential index which, unlike energy expenditure, is not device-specific and (ii) system-wise an energy-efficient system of flows is not always a better choice: we show that a less energy-efficient system may be more reliable in terms of packet multiplexing and, in turn, may reduce the probability that some flows may expend their energy with zero gain. We present results using a real testbed

Theintegration oftheInternet withwireless, satellite andhigh-speed components along withtheincreasing useofbattery-powered devices andad-hoc andsensor networking, calls foranewprotocol design perspective. Protocols atthetransport layer needtomanagethecomplexity ofvarying orevenconflicting userrequirements butalso needtointerpret correctly theunderlying signals fromvarious networks. In thiscontext, we discuss protocol strategies andperformance issues, aswellas architectural perspectives forthenextgeneration Internetworking. We gobeyond typical discussion, tocommentonthevarious network research directions today. Aboutthespeaker: Vassilis Tsaoussidis received a B.ScinApplied Mathematics fromAristotle University, Greece; aDiploma inStatistics andComputer Science fromtheHellenic Institute ofStatistics; andaPh.DinComputer Networks fromHumboldt University, Berlin, Germany(1995). Vassilis heldfaculty positions inRutgers University, New Brunswick, SUNY Stony BrookandNortheastern University, Boston. InMay2003, Vassilis joined theDepartment ofElectrical andComputer Engineering ofDemocritus University, Greece. Vassilis istheEditor-in-Chief forthenewjournal ofInternet Engineering, and editor forthejournals IEEETransactions inMobile Computing, Computer Networks, Wireless Communications andMobileComputing, Parallel, Emergentand Distributed Systems andMobileMultimedia. He isa memberofthesteering committee ofWWIC,chaired several conferences andjoined several Technical Program Committees suchasINFOCOM,GLOBECOM,Networking, ICCN,ISCC, EWCN,WLN,andseveral others.

We observe that even when the system throughput is relatively stable,end users of media-streaming applications do not necessarily experience smooth throughput, due to the unsynchronized window adjustments triggered by random congestion indications. We analyze and evaluate the negative impact of random window adjustments on smoothness, short-term fairness, and long-term fairness. We further propose an experimental congestion avoidance mechanism, namely TCP(/spl alpha/, /spl beta/, /spl gamma/, /spl delta/), based on coordinated window adjustments. The flow-level smoothness is enhanced significantly for media-streaming applications, without a cost on fairness and responsiveness. Responsiveness is even boosted when bandwidth is underutilized.

We show that TCP timers, based solely on RTT estimations and measurements, cannot capture with precision the level of flow contention. We notice that increased contention may stabilize RTT variation, minimize the deviation and, in turn, shorten the timeout. We show that this behavior is undesirable indeed, since it leads to unfair resource utilization. We propose CA-RTO, an algorithm that incorporates a contention parameter and a randomization technique into the retransmission timeout. We report significant improvement in fairness, great reduction of retransmitted packets and slight improvements in application goodput.

We evaluate the impact of network, and protocol heterogeneity on real-time application performance. We focus on TCP and UDP supportive role, also in the context of network stability and fairness. We reach several conclusions on the specific impact of wireless links, MPEG traffic friendliness, and TCP version efficiency. Beyond that, we also reach an unexpected result: UDP traffic is occasionally worse than TCP traffic when the right performance metric is used.

Additive increase/multiplicative decrease-based protocols, including transmission control protocol (TCP), TCP-friendly, and a new generation of rate-based protocols, attempt to control the tradeoff of responsiveness and smoothness. Traditionally, smoothness has not been a main concern since it does not impact the performance of regular Internet applications such as the Web, FTP, or e-mail. However, multimedia-driven protocols attempt to favor smoothness at the cost of responsiveness. In general, smoothness and responsiveness constitute a tradeoff; however, we uncover undesirable dynamics of the protocols in the context of wireless/mobile networks with high-error rate or frequent handoffs: low responsiveness is not counterbalanced by gains in smoothness, but instead, produces a conservative behavior that degrades protocol performance with both delay-tolerant and -sensitive applications. Based on our observations, as well as on further analysis of the impact of the bottleneck queue on channel utilization, we seek an alternative strategy for smooth window adjustments. We introduce a new parameter /spl gamma/, which implements a congestion avoidance tactic and reaches better smoothness without damaging responsiveness.

We investigate the behavior of TCP(/spl alpha/,/spl beta/) protocols in the presence of wireless networks. We seek an answer to strategic issues of maximizing energy and bandwidth exploitation, without damaging the dynamics of multiple-flow equilibrium. Our perspective is novel indeed: What is the return of the effort that a protocol expends? Can we achieve more gains with less effort? We study first the design assumptions of TCP(/spl alpha/,/spl beta/) protocols and discuss the impact of equation-based modulation of /spl alpha/ and /spl beta/ on protocol efficiency. We introduce two new metrics to capture protocol behavior: The "extra energy expenditure" and the "unexploited available resource index". We confirm, by simulation experiments, that, in general, smoothness and responsiveness constitute a tradeoff; however, we show that this tradeoff does not graft its dynamics into a conservative/aggressive behavior, as is traditionally believed. We uncover patterns of unjustified tactics; our results suggest that an adaptive congestion control algorithm is needed to integrate the dynamics of heterogeneous networks into protocol behavior.

We introduce an alternative approach to congestion avoidance and control, which has the potential to increase efficiency and fairness in multiplexed channels. Our approach, bimodal congestion avoidance and control, is based on the principles of TCP's additive increase multiplicative decrease. It is designed to better exploit the system properties during equilibrium, without trading off responsiveness for smoothness. In addition, it is capable of achieving convergence to fairness in only two congestion cycles. As a result, both efficiency and fairness are improved, responsiveness is not degraded, and smoothness is significantly improved when the system is in equilibrium. We provide a theoretical analysis and we discuss the potential of our approach for packet networks. Our experiments confirm that bimodal congestion avoidance and control as a component of the transmission control protocol outperforms the traditional scheme.

In this work we first describe an asynchronous-feedback model which corresponds to the diverse round-trip times (RTTs) of competing flows within the same communication channel. We show that even when the feedback of the receivers/network is asynchronous, the duration of a congestion epoch represents "common knowledge" for the competing flows. Based on this property, we propose a diverse linear increase scheme in proportion to the RTT of each flow and we adjust periodically the windows of the competing flows accordingly, in order to enhance fairness of asynchronous-feedback environments. We name this scheme /spl tau/-AIMD and show that fairness of flows in asynchronous systems is improved since the increase-rate diversity of long and short RTT flows is largely canceled. We use the max-min notion of fairness to show that /spl tau/-AIMD can constitute the foundation for other window-based, end-to-end algorithms that target a good balance between efficiency and fairness.

In this paper, we observe that although multiplicative decrease is necessary to accomplish fairness in congestion control, it does not inevitably sacrifice system throughput, as long as the system operates between the knee and the cliff, according to an equation. However, even when the system throughput is relatively stable, end users of real-time applications do not necessarily experience a smooth traffic, mainly caused by the unsynchronized window adjustments due to random congestion indications. We analyzed and evaluated the negative impact of random window adjustments on smoothness, short-term fairness, and even long-term fairness measured by a novel fairness metric defined in this paper. Therefore, we propose an experimental congestion avoidance mechanism to improve TCP smoothness for media-streaming applications. The mechanism relies on a fine-grained RTT estimation to measure the network condition, and coordinates the upward and backward window adjustments to abolish the damage of unsynchronized window control. Congestive packet drops are reduced by a new control parameter g, and the bottleneck queue length can also be controlled in an end-to-end way. Simulation results confirm that the new mechanism enhance significantly the smoothness and fairness, without a cost of responsiveness. In fact, by enabling a new parameter d, the responsiveness can be even enhanced when the bandwidth is under-utilized.

TCP(/spl alpha/,/spl beta/) protocols trade the congestion window increase value /spl alpha/ for the decrease ratio /spl beta/, to generate smoother traffic patterns and to maintain a friendly behavior. We study the design assumptions of TCP(/spl alpha/,/spl beta/) protocols and discuss the impact of equation-based modulation of /spl alpha/ and /spl beta/ on application efficiency. We confirm experimentally that, in general, smoothness and responsiveness constitute a tradeoff; however, we uncover undesirable dynamics of the protocols when the network or flow characteristics do not follow a prescribed and static behavior. For example, we show that smooth backward adjustments confine the protocol's capability to exploit resources that become available rapidly, and embarrass the fair and efficient growth of incoming flows. Furthermore, we show that in the context of wireless networks with high error rate, a low /spl alpha/ dictates a conservative behavior that degrades the protocol performance with both delay-tolerant and delay-sensitive applications; and in the context of high contention of heterogeneous flows, a low /spl alpha/ does not contribute to efficiency and friendliness.

TCP error control mechanism lacks the ability to detect with precision the nature of potential errors during communication. It is only capable of detecting the results of the errors, namely, that segments are dropped. As a result, the protocol lacks the ability to implement an appropriate error recovery strategy cognizant of current network conditions and responsive to the distinctive error characteristics of the communication channel. Our experiments have three distinct goals. First, to demonstrate the potential contribution of probing mechanisms. A simple probing mechanism and an immediate recovery strategy are grafted into TCP-Tahoe and TCP-Reno. We show that, this way, standard TCP can improve its performance without requiring any further change. Second, to study the performance of adaptive strategies. An adaptive TCP with probing is used, that is responsive to the detected error conditions by alternating slow start, fast recovery and immediate recovery. An adaptive error recovery strategy can yield better performance. Third, to study the design limitations of the probing device itself. The aggressive or conservative nature of the probing mechanisms themselves can determine the aggressive or conservative behavior of the protocol, respectively.

In recent years mobile computing has experienced significant growth, mainly due to the integration of wireless networks with the wired Internet. This integration itself experienced several stages of evolution: from the functional issues of network heterogeneity to the optimization of the Internet protocols. Currently, the design issues of reliable protocols for mobile computing possess a fundamental locus. More precisely, performance evaluation, throughput optimization, energy saving, and network/device functionality within the layered Internet call for further attention. Within this context, this special issue addresses the design concerns of reliable protocols for mobile computing. We have selected seven papers for presentation in the special issue, from a large pool of submitted papers in response to our call for papers. The first paper, authored by the guest editors, discusses open issues on the design of the dominant Internet protocol, the Transmission Control Protocol (TCP). The paper classifies the recent work based on the functionality of the proposed modifications, realizes the need for new performance metrics and presents selected results of two recent approaches to mobile TCP, namely TCP-Probing and WTCP. The paper by Eckhardt and Steenkiste investigates the possibility of dealing with wireless link errors by combining a link-level local error control with error-sensitive link scheduling. Having a direct target the improvement of TCP over wireless networks, Chen, Hsiao, Hou, Ge, and Fitz propose the use of Syndrome. Syndrome is a light-weight approach to improving TCP's throughput performance. The combination of TCP's sequence numbers and the additional base station-attached numbers allow for detection of the error's location (i.e., wired vs. wireless). This is a significant step toward error correction especially owing to the fact that the base station does not need to buffer packets or a significant amount of states. Vaidya, Mehta, Perkins, and Montenegro propose an alternative TCP-unaware technique where the wireless client delays duplicate acknowledgments to avoid fast retransmit at the sender. This is in sharp contrast to TCP-aware techniques such as Snoop. Along the lines of performance evaluation, the paper by Xu and Saadawi compares the performance of various TCP versions over ad-hoc (multi-hop wireless) networks and suggests appropriate parameter tuning in order for those versions to behave appropriately. Emphasizing the energy/throughput tradeoff, Zorzi, Rossi, and Mazzini investigate the performance of TCP over wideband CDMA air interface. Such interfaces are typical of third-generation wireless networks. The authors introduce a universal throughput curve and exploit the possibility of selecting an optimal power control threshold thereby optimizing the tradeoff between throughput gains and energy expenditure. Finally, to deal with reliable handoffs, the paper by Jobin, Tripathi, Gokhale and Faloutsos quantifies the effectiveness of a predictive reservations scheme using metrics which characterize the mobility profile of users. We would like to offer special thanks to the reviewers and to the authors for their contribution to this special issue.

Abstract We discuss the design principles of TCP within the context of heterogeneous wired/wireless networks and mobile networking. We identify three shortcomings in TCP's behavior: (i) the protocol's error detection mechanism, which does not distinguish different types of errors and thus does not suffice for heterogeneous wired/wireless environments, (ii) the error recovery, which is not responsive to the distinctive characteristics of wireless networks such as transient or burst errors due to handoffs and fading channels, and (iii) the protocol strategy, which does not control the tradeoff between performance measures such as goodput and energy consumption, and often entails a wasteful effort of retransmission and energy expenditure. We discuss a solution‐framework based on selected research proposals and the associated evaluation criteria for the suggested modifications. We highlight an important angle that did not attract the required attention so far: the need for new performance metrics, appropriate for evaluating the impact of protocol strategies on battery‐powered devices. Copyright © 2001 John Wiley & Sons, Ltd.

We report results on the efficiency of error recovery strategies over heterogeneous networks with both wired and wireless components. We investigate the relative impact of end-to-end delays and error patterns on protocol performance for three broad categories of protocol behavior: aggressive, conservative and adaptive. We monitor the network behavior using varying error conditions and we set end-to-end delays ranging from 10 to 200 ms in order to capture delay characteristics of wired, wireless and satellite networks. We show that (i) the end-to-end delay has varying impact on protocol performance. This impact depends on the recovery strategy, the error rate and the error type. (ii) Standard TCP Reno and Tahoe mechanisms that implement their respective recovery strategies display conflicting patterns of behavior, that might not conform to network conditions nor to their strategic goals. (iii) Adaptive behavior yields better results when a protocol flexibly alternates conservative and aggressive strategies based on the error pattern detected and the end-to-end delay. We Support this conclusion with the results of TCP-Probing.

We present a TCP-compatible and -friendly protocol which abolishes thr ee major shortfalls of TCP for reliable multimedia applications over heterogeneous networks: (i) ineffective bandwidth utilization, (ii) unnecessary congestion-oriented responses to wireless link errors (e.g., fading channels) and operations (e.g. handoffs), and (iii) wasteful window adjustments over asymmetric, low-bandwidth reverse paths. We propose TCP-Real, a high-throughput transport protocol that minimizes transmission-rate gaps, thereby enabling better performance and reasonable playback timers. In TCP-Real, the receiver decides with better accuracy about the appropriate size of the congestion window. Slow Start and timeout adjustments are used whenever congestion avoidance fails; however, rate and timeout adjustments are cancelled whenever the receiving rate indicates sufficient availability of bandwidth. We detail the protocol design and we report significant improvement on the performance of the protocol with time-constrained traffic, wireless link errors and asymmetric paths.

Today's universal communications increasingly involve mobile and battery-powered devices (e.g. hand-held, laptop) over wired and wireless networks. Energy efficiency as well as throughput, are becoming service characteristics of dominant importance in communication protocols. Although standard TCP versions lack the functionality to efficiently adjust their error-control strategies to distinct characteristics of network environments and to specific constraints of communicating devices, the wide range of TCP-based applications have rendered TCP the de facto standard for reliable end-to-end communications. In this work we propose "grafting" two components of strategic significance onto standard TCP: a probing mechanism and an immediate recovery strategy. Our results show that these enhancements yield higher throughput while maintaining lower levels of energy expenditure, and thus have the potential of promoting TCP's congestion control to a universal error control schema for heterogeneous wired/wireless channels. Furthermore, the enhancements do not damage the end-to-end characteristics of the TCP, nor do they require changes to its semantics: the mechanism are implemented as option extensions to the TCP header. We compare "TCP-probing" with Tahoe, Reno, and New Reno, and show that is can be a protocol of choice for heterogeneous wired/wireless communications with respect to energy and throughput performance.

Today's universal communications increasing involve mobile and battery-powered devices (e.g. hand-held, laptop, IP-phone) connected over wired and wireless networks. Energy efficiency, as well as throughput are becoming service characteristics of dominant importance in communication protocols. The wide applicability of IP-networks/devices, and the wide range of TCP-based applications, have rendered TCP the de facto reliable transport protocol standard not only for wired, but also for wireless and mixed (wired/wireless) communications. TCP's congestion control algorithms have been refined to achieve higher throughput. Even with these modifications, however, TCP versions do not incorporate a flexible error recovery strategy that is responsive to distinct environmental characteristics and device constraints. We have compared the energy- and throughput-efficiency of TCP error control strategies based on results gathered from our implementation of TCP Tahoe, Reno, and New Reno. We show that, depending on the frequency and duration of the error, each demonstrates appropriate behavior under specific circumstances, with Tahoe more-or-less the most energy conserving of the three. None of them, however, possesses a clear-cut overall advantage that would render it the version of choice for wired/wireless heterogeneous networks.

This work involves the development of an experimental transport-level protocol running on top of IP for small, mobile, wireless stations. The protocol cannot and does not aim to handle real-time traffic. Its central concern is to conserve battery-powered energy used for transmission, even at the expense of slower data throughput. It attempts to conserve energy expenditure by adjusting the amount of data transmitted, trying to keep it below perceived network congestion. The higher the detected congestion risk-level in the network the less it attempts to transmit thereby minimizing the need for duplicate data retransmission due to congested routers losing packets and so on. We outline the protocol specification, mechanisms and implementation, as well as preliminary evaluation results that clearly demonstrate the energy-saving capabilities of the protocol.

With the advent of distributed computing, application management is driven into a new era. In this world, application quality of service, resource availability at different domains, and user requirements, are combined in a dynamic, synergistic, and geographically broad cooperation. We present an architecture and initial implementation of a middleware that satisfies user requests according to expected requirements, distributes networked resource load beyond the local environment, and respects the logical constraints of different domains. Static characteristics of resources are advertised as service offers using the CORBA trading service, while dynamic changes in their state are reported using the CORBA event service. We present a model where, unlike traditional high-level management systems, resources compete to satisfy application requirements.

The use of application management systems has become a valuable approach in dealing with dynamic information filtering, resource allocation, and resource control. Traditionally, management systems provide the application or the user with capabilities to statically monitor and control the resources. This work presents a knowledge-based management system that offers dynamic service to distributed applications as well as dynamic control of the application's environment. It also studies the roles of different agents in an application management environment. The presented framework deals with heterogeneity of distributed environments and enables agents to utilize dynamic information regarding the resources. Agents are used as resource administrators, application agents and user agents. They utilize control mechanisms to manage the resources with respect to the application requirements, control the user's environment and monitor-control-report management information. The paradigms of control mechanism presented here exploit the agent capabilities and their communication environment.