QUIC is emerging as the de facto transport protocol for modern applications and forms the basis of HTTP/3. Within the European Space Agency (ESA) project QUICoS, we developed QUIC-Wave, a satellite-tailored extension of QUIC designed to address the limitations of TCP-based transport in high-latency and lossy satellite environments (GEO, MEO, LEO). Unlike Performance Enhancing Proxy (PEP) approaches, QUIC-Wave preserves end-to-end semantics and encryption while enhancing congestion control. The protocol extensions are engineered to sustain throughput and responsiveness under satellite-specific conditions such as long RTTs, bandwidth variability, and mobility-induced handovers, while maintaining compliance with QUIC specifications and interoperability with terrestrial networks. To validate QUIC-Wave, we conducted extensive real experiments using standard browsers and servers. Results show that QUIC-Wave supports interactive web browsing and multimedia streaming with improved performance over satellite links, without compromising either end-to-end encryption or protocol integrity.

Wave is a disruptive rate control protocol based on the burst transmission paradigm, developed in the Linux kernel for TCP. The main technical innovation leverages a burst-based transmission against the traditional Congestion Window ( cwnd ) paradigm, demonstrating good performance in harsh communication scenarios and supporting common Web applications. Recently, the advent of QUIC moved congestion and loss control up to the application layer, using UDP as transport protocol. Such a migration implied the adaptation and validation of the CCAs within the QUIC framework, based on new data encapsulation methods of both data and acknowledgment frames, and new timers with user space granularity, enabling various options for error control and bandwidth estimation, mainly tailored to BBR. The latter, together with Cubic and NewReno, are the current QUIC CCA. In this context, the original contribution of the paper includes the adaptation of the Wave algorithm within the QUIC implementation and the verification of its better effectiveness with respect to the CCAs already included in the latest QUIC implementations. In particular, an enhanced Wave algorithm has been designed and adapted to QUIC, adding a new state named “recovery mode” to handle possible ACK frame encapsulation into QUIC packets. The resulting QUIC Wave has been implemented in ngtcp2 and integrated into a network testbed, allowing extensive performance evaluation over different challenging communication scenarios for an exhaustive protocol validation. Results confirm the TCP Wave working principles and the overall performance efficiency, paving the way for future experimentation on real networks.

Traditional transport layer protocols, such as TCP and UDP, have long served as the foundation for Internet communications. In particular, TCP seeks to avoid network congestion through a Congestion Control Algorithm (CCA), which typically relies on outdated paradigms, such as ACK-clocked transmission and congestion window regulation based on packet loss. Recently, the standardization of QUIC by the IETF has led to a more flexible and efficient transport protocol, offering integrated security, reduced signaling latency, and multiplexing capabilities. Within this evolving landscape, TCP Wave (TCPW) emerged as a novel transport-layer protocol that adopts different CCA paradigms with respect to traditional ones. Decoupling transmission from ACK reception and adopting a burst-based proactive congestion control strategy, Wave presents a promising direction for next-generation network protocols.This paper addresses the feasibility of integrating TCP Wave’s core principles into the QUIC protocol. We provide an overview of the TCP Wave congestion control algorithm and evaluate a preliminary implementation across two representative QUIC stacks. Through an experimental analysis, we examine the impact of burst transmission on throughput and acknowledgment behavior. The results of this study may serve as a foundational step towards the full implementation of the Wave CCA within the QUIC protocol, laying the groundwork for future research on congestion control within QUIC.

Current 3GPP specifications (Rel. 17) enable connectivity to the 5G core network through alternative non-3GPP access technologies (e.g., WiFi), introducing also the support of multicast and broadcast services, but only within the New Radio (NR) framework. Thus, the standard leaves a significant gap when users want to access multicast and broadcast services through non-3GPP access networks.In a near future, when heterogeneous connectivity will be the norm and device density continues to grow, this limitation may hinder efficient content distribution and strain unicast-dominated infrastructures.This paper envisions a future in which multicast and broadcast services are natively integrated into the non-3GPP access domain, enabling smarter resource allocation and reduced bandwidth consumption. We outline key technical challenges, propose architectural considerations, and explore the transformative potential of unified multicast services in next-generation multi-access 5G environments.

The fifth-generation (5G) mobile network is designed to provide a better user experience than its predecessors. To reach this goal, in addition to the standard radio access, it is foreseen that users can connect to 5G services via different access networks (e.g., Wi-Fi), through the well-defined non-3GPP access technology. Based on some security aspects, it can be distinguished as trusted and untrusted non-3GPP access.This paper aims to show how to improve overall 5G non-3GPP access performance by optimizing data rate and strengthening security, achieved through the selection of the most suitable ciphering and authentication algorithm combination. After providing a detailed comparison between trusted and untrusted access types and related differences, we describe how to maximize the available bandwidth using fast and secure IPSec authentication and encryption algorithms, ensuring an optimal trade-off between performance and security. A surprising outcome of this study reveals that, although users are expected to experience higher data rates on trusted non-3GPP access due to the absence of encryption overhead, the use of new-generation ciphers such as AEAD (Authenticated Encryption with Associated Data), which ensures both confidentiality and message authenticity through a single, efficient operation, can achieve up to a twofold increase in throughput compared to historical approaches considering encryption and authentication as separate operations.

The Integrated Access Backhaul (IAB) is deemed to reduce the deployment costs of ultra-dense 5G millimetre-wave (mmWave) networks, using wireless backhaul links to relay the access traffic. ESA funded the project SATIABLE to investigate technical issues to use the satellite for this kind of service, aiming to draw recommendations for IAB features or extensions for scenarios integrating NTN networks, to provide an analytical baseline and a simulation tool for the assessment of benefits for further studies towards the 3GPP Release 18. The paper briefly describes the project objectives and outcomes.

Network virtualization and centralized resource orchestration is gaining importance thanks to cutting-edge 5G communication paradigms. Although satellite networks are often characterized by legacy technologies customized for specific application requirements, an update of the satellite platforms following the process encompassed by the mobile network operators can help a future efficient integration of terrestrial and satellite resource to offer added-value services. The main objective of the SURPRISE project, funded by ESA, is the virtualization of the satellite gateway, which is of paramount importance, needing a careful design, development and testing of the ground software components to control, manage and share combined digitalized services/resources provided by flexible high throughput satellites and terrestrial networks to multiple end users and service providers. It just ended the reference scenario definition phase, arriving to valuable results to share with the scientific community. Thus, the aim of this paper is to describe the use cases and the reference scenarios so far defined.

The optimization of transport protocols over satellite links represents a significant issue and target of research since many years. A lot of work has been carried out on TCP that, for a very long time, has been the basis of most of the applications running on the Internet. Recently, new applications are instead based on UDP, with specific reference to QUIC and the associated HTTP/3 protocols. In this regard, TCP long history of optimizations and enhancements (normally implemented in the operating systems), are not yet fully available in QUIC. Since QUIC protocol appears to be a very promising solution and it is expected to become the reference protocol for most of the future Internet applications, it requires adaptation and further investigation with the aim to make it work efficiently in any network configuration, in the same way as TCP already does. The paper approaches possible QUIC limitations and design optimizations to make it effective in satellite-based networks, inheriting existing TCP based optimizations or introducing new ones.

As the telecommunications industry embarks on the transition to Sixth-Generation (6G) networks, this paper examines the integration of Non-Terrestrial Networks (NTN), and in particular satellite backhauling, in the context of Fifth-Generation (5G) systems. The Integrated Access and Backhaul (IAB) technology, conceived as a wireless terrestrial backhauling system in the Next Generation Radio Access Network (NG-RAN), has been identified as a possible enabler for the integration of satellite nodes. Despite the work already done in this direction, the combination of IAB architectures with satellite nodes operating in both the access and backhaul side requires further evaluations on feasibility and limitations for networks integrating Low Earth Orbit (LEO) and Geostationary Earth Orbit (GEO) satellites. To this end, this work contributes providing insights on background technologies, as well as a detailed analysis of the issues and challenges arising from such integration and a definition of use cases to support narrow-band and broadband services. Furthermore, the design and implementation of a simulation tool is proposed for a performance evaluation in terms of registration time, link capacity, single-hop and end-to-end delay. Results show that the integration turns out to be feasible, even if with strong constraints coming from the satellite system rather than the IAB usage itself. Indeed, the earth-satellite link in LEO systems has a significant impact on the packet delivery time due to the discontinuous coverage. In case of GEO satellite instead, a non-terrestrial backhaul link could limit the performance of the whole system, especially at lower elevation angles.

Reliable communications play a pivotal role in ensuring an efficient response and the coordination of recovery and rescue efforts. However, conventional communication methods may not always be accessible or dependable in such situations. In such circumstances, constellations of Low Earth Orbit (LEO) satellites can provide high bandwidth capabilities with relatively low latency, making them well-suited for supporting on-the-ground disaster management teams. Satellites can either complement or replace terrestrial telecommunication infrastructures. In this context, reliance on the recently defined QUIC protocol allows for a seamless transition from terrestrial to satellite communication as needed. Therefore, we investigate the possible use of a dual-stack node architecture along with the employment of the QUIC transport protocol for emergency communications, assuming that the backhaul link used to transfer users’ applications data may need to be changed (seamlessly). We conduct an extensive emulation study, evaluating the performance of QUIC under varying queuing policies and Congestion Control Algorithm (CCA) behaviour, providing practical insights and recommendations to enhance the protocol’s efficiency and robustness. The key aspects and configurations of QUIC protocol stack are identified, presenting optimal communication configurations leveraging CoDel and BBR CCA.

The 3GPP standardized a new architecture and procedures for the NG-RAN to extend the network coverage to those hidden or unreachable areas. It consists in a distributed topology of low-complexity and low-cost network nodes named Integrated Access and Backhaul (IAB). The IAB is defined in Rel-16 and enhanced in Rel-17 and allows to distribute the gNB element in multiple Distributed Units (nodes) controlled by a Central Unit (donor) directly connected with the core network. This architecture is designed to relay the radio signal of the UE leveraging a wireless backhaul. Furthermore, enhancements for the mobile-IAB are expected in the Rel-18, in particular assuming nodes mounted on top of moving vehicle which can be either Terrestrial or Non-Terrestrial. Similarly, the 3GPP published a study which identified some appealing use cases where Non-Terrestrial Networks (NTN), in particular the satellite, can be exploited to relay the radio signal of the UE in areas unserved or uncovered by Terrestrial networks. The integration of a satellite component in this scenario may be a further confirmation of its added value and the support that could be provided in mobile networks. First steps were already moved with the definition of two frequency bands for the Satellite Access Node (SAN) operations by 3GPP in Rel-17, while further enhancements are expected for 6G networks. This paper briefly reports the key aspect of the IAB technology and will investigate possible architectures including a satellite components. Two main integration approaches will be evaluated analysing possible adaptations required for SatCom in direct access.

5G aims at providing significant improvements to mobile networks with regard to previous 4G ones, in both performance and flexibility. Indeed, a 5G network is expected to increase throughput and reduce latency, leveraging softwarization and virtualization concepts and the state of the art in radio access and resources allocation. A 5G system (5GS) long-term goal is to address more and more challenging and broader use-cases, allowing a multi-tenant use (slicing) of the same physical infrastructure to enable and deploy at the same time ultra-reliable and low latency, machine-type or broadband communication services. In that context, network resources are highly abstracted and require complex management operations, which ultimately must be reflected downwards to the physical resources. In supporting that task, since 3GPP Rel-16, a network function called Network Data Analytics Function (NWDAF) was introduced, with the primary goal of collecting and processing heterogeneous data coming from the User Plane of the 5GS. The NWDAF outputs can then be used to perform network reconfigurations and automation in general, optimizing traffic management and overall network performance. In this paper we present which realtime metrics can be collected by a NWDAF and how, in a reference 5G core network, validating the correctness of the measurements performed using real traffic in a Linux-based testbed.

5G represents the latest currently available and the state of the art of mobile cellular networks. 5G is defined on the basis of new concepts like Software Defined Network (SDN), Network Function Virtualization (NFV) and Network Slicing, enabling a wide set of use-cases and applications. An innovative feature introduced in 5G since 3GPP Release 16 is Access Traffic Steering, Splitting and Switching (ATSSS), which gives the possibility to the user equipment (UE) connected to a 5G network using a 3GPP link (i.e., the gNB New Radio access) and a non-3GPP one (e.g., a public WLAN access point) to access 5G services using both links simultaneously. ATSSS can improve the user-experience, maximizing the throughput and improving resilience to network faults by downloading or uploading data using both channels at the same time or selecting the best link where to transmit for each data flow. In this paper, we analyze in depth the ATSSS functionality and the associated Multipath TCP (MP-TCP) mode in a Linux simulation testbed, including an Open Source 5G Core Network, with the full implementation of the User Plane and 3GPP and non-3GPP access links, using Free5GC, UERANSIM and a custom implementation of N3IWF. In this testbed setup, we run real traffic and assess the MP-TCP configuration and performance in realistic conditions, when the non-3GPP access is performed wither via terrestrial wireless or a high latency satellite link.

The 5G service-based architecture brought a high degree of flexibility in the dynamic network management and configuration, enabling several Network Functions (NFs) cooperating to customize a communication service based on requirements of a specific vertical. Since rel. 15, the 3GPP introduced a Network Data Analytic Function (NWDAF) for the collection of data from other NFs and the delivery of data analytics services. This paper addresses a compelling use case with a hybrid satellite terrestrial backhaul, with the NWDAF that can be used to catch the slice statistics on the user plane and to drive the enabling of a supplementary satellite backhaul link for performance optimization in compliance with the service requirements. Thus, an optimized configuration of the 5GC is proposed highlighting the NFs involved in the analytics as well as the data sources and the data interfaces.

5G is a cornerstone in the evolution of mobile communication networks, representing the most advanced and available standard at the state of art. Characterized by higher data rate and capacity, actually the real revolution of 5G relies in its capability to offer advanced and heterogeneous services by the full abstraction and slicing of network resources, realizing a service-oriented full-IP high-performance network over a common infrastructure, even belonging to different operators. Another key aspect, which is specifically addressed in this paper, is the possibility to access the services offered by the 5G network using non-3GPP access, and in particular Wi-Fi. This feature can allow access from home Access Points or using public Hotspots, even where there is no 5G coverage or roaming. At the same time, other types of IP access, including terrestrial wired options, are allowed by 3GPP specifications. Such a flexibility allows, although not explicitly mentioned, to consider as well satellite-based non-3GPP access methods, thus enabling wide-coverage use-cases and rural areas coverage. In the paper we discuss the network function required to enable non-3GPP access to 5G Core Networks, namely N3IWF, and the impact in using as access network a VSAT satellite link. After a focus on protocol stacks and signalling procedures, we implemented such an access on a real time Linux testbed including a 5G rel. 15 compliant Core Network, a N3IWF network function and a satellite emulation to assess control procedures timings, User plane latency and overhead.

The adoption of the Narrowband-Internet of Things technology in satellite communications intends to boost Internet of Things services beyond the boundaries imposed by the current terrestrial infrastructures. Apart from link-level studies in the scientific literature and preliminary 3GPP technical reports, the overall debate is still open. To provide a further step forward in this direction, the work presented herein pursues a novel service-oriented methodology to design an effective solution, meticulously stitched around application requirements and technological constraints. To this end, it conducts link-level and system-level investigations to tune physical transmissions, satellite constellation, and protocol architecture, while ensuring the expected system behavior. To offer a real smart agriculture service operating in Europe, the resulting solution exploits 24 low-Earth orbit satellites, grouped into eight different orbits, moving at an altitude of 500 km. The configured protocol stack supports the transmission of tens of bytes generated at the application layer, by also counteracting the issues introduced by the satellite link. Since each satellite has the whole protocol stack onboard, terminals can transmit data without the need for the feeder link. This ensures communication latencies ranging from 16 to 75 min, depending on the served number of terminals and the physical transmission settings. Moreover, the usage of the early data transmission scheme reduces communication latencies up to 40%. These results pave the way toward the deployment of an effective proof of concept, which drastically reduces the time to market imposed by the current state of the art.

Satellite communications (SatCom) have a role of advanced service enablers in the new virtual networks, following 3GPP specifications. Specifically, the satellite peculiar characteristics are of paramount importance to dynamically activate capabilities, such as multicast and broadcast channels, sudden traffic offloading, capacity bonding, and cost-efficient coverage of uncovered areas. A key aspect to achieve a seamless and efficient integration between satellite and terrestrial infrastructures is to make satellite resource management dynamic and with a centralised control of a single orchestrator that has visibility of the end-to-end network. Considering the adoption of Software Defined Networking (SDN) and Network Function Virtualization (NFV) paradigms and the upcoming 5thgeneration of mobile communications (5G), this paper presents the ongoing work within the European Space Agency (ESA) ANChOR project, whose main output will be a data-driven Network Controller and Orchestrator for SatCom networks. This tool will be based on Artificial Intelligence (AI) / Machine Learning (ML)-based techniques to properly allocate resources exploiting some feedback knowledge of the network and it aims to support different services over 5G integrated satellite-terrestrial networks.

The management of public utilities represents a complex issue even in normal operational conditions. In case of emergency the degree of complexity increases exponentially and the variables to take into account, the data to process, the useful expected outcomes and the decision processes need to be supported by technology.For these reasons, the eUmaP project aims to design and develop an open platform through which local authorities will be able to plan and manage the demand and supply of building utilities in case of quarantine or lock down. It will be based on the rational of Earth observation, and the recording of the required network information in open BIM platforms of five European capital cities (Rome, Berlin, Athens, Vilnius, Nicosia).The paper is focused on the architecture definition discussing the pros and cons of three different architectural schemes.

The advent of 5G with the three identified use case classes (eMBB, mMTC, URLLC) requires to adequately define system architectures including all the technological segments that can contribute to satisfactorily reach the target performance. For this reason, satellite systems must be duly considered because their intrinsic characteristics are well suitable to support 5G services. In particular, as concerns mMTC/NB-IoT class an ongoing ESA project is demonstrating the feasibility and the usefulness of the inclusion of the satellite segment in the system architecture and has identified peculiar use cases. The paper presents some of the outcomes of the project so far achieved, both in terms of scenario identification and implementation issues in compliance with 3GPP standard architectures.

The QUIC (Quick UDP Internet Connection) protocol suite is going to approach its final stages of standardization to become part of the official Internet standards (RFCs) and of the new HTTP/3 specification. Some of its disruptive characteristics, such as the 0-RTT establishment of secure communications and a connection-oriented management over a UDP-based connection-less transport, can be reused and tailored in the framework of a Performance Enhancing Proxy (PEP) architecture for the effective management of multiple links. In this paper, we describe the design and implementation of a QUIC-based splitting solution to enhance the communication across multiple backhaul links, each associated with a different network technology (e.g., satellite and terrestrial). After discussing the working principles of the designed QUIC-based proxy, we present a software implementation, as well as preliminary results obtained, through a set of meaningful test-cases deployed over a Linux based testbed.

In the definition of advanced 5G scenarios, one of the possible configurations including the satellite link is to consider it to provide a supplementary capacity to enhance backhauling towards data networks. The peculiar satellite physical characteristics and the resulting challenging communication environment (i.e., large propagation delays, possible losses, etc.) are usually tackled with the introduction of Performance Enhancing Proxies (PEPs) agents aimed to improve performance. In this regard, 5G offers the cutting-edge capability to exploit virtualization and slicing concepts, so that PEP can be implemented as a set of Virtualized Network Functions (VNFs) to be dynamically deployed into the network responding to the specific requirement of the target service slice. In this paper we discuss this approach, validated in the frame of an European Space Agency (ESA) project, where a hybrid terrestrial-satellite backhaul is envisaged to enhance performance and system. In particular, we present a QUIC proxy as distributed VNFs aimed to efficiently manage the hybrid link allowing an efficient failover in case of terrestrial link outage or unavailability.

Contention Resolution Diversity Slotted ALOHA (CRDSA) random access scheme, introduced in the DVB-RCS2/NG standard, is specifically designed to support the transfer of a variety of traffic profiles that Machine to Machine (M2M) and Internet of Things (IoT) applications may generate. Protocols for M2M and IoT has recently receiver substantial upgrades, but still mainly designed with an underlying terrestrial network in mind. If clusters of sensor nodes exchange data via satellite terminals toward a sink via short-lived TCP/IP connections, many shortcomings may incur. This work aims at investigating in details the behavior for such data transfer in presence of a shared random access channel, and the advantages when using a new TCP version specifically designed for satellite links, namely TCP Wave. In particular, through a detailed simulation campaign based on the NS3 simulator, this work assesses the completion time of data delivery for M2M elastic traffic via CRDSA satellite random access, when standard TCP (NewReno) or dedicated satellite TCP (Wave) is adopted.

Telecommunication networks are complex systems in term of design, development, management and maintenance. The degree of complexity greatly increases when the network is composed of several segments adopting different technologies and standards, as well as the sharing of common resources. Development of suitable models of networking and their implementation using simulation and emulation tools are of paramount importance to address such a complexity in a laboratory-controlled environment. To tackle different aspects of satellite and terrestrial integrated networks, which cover different protocol layers and technology standards, different simulative or emulative approaches are possible. A presentation and selection of simulation and emulation tools is presented in this paper, followed by the description of results obtainable with the selected tools in some explicative study-cases.

TCP Wave changes the typical TCP transmission paradigm by replacing the ACK-clocked sliding window with self-scheduled bursts. In response to bursts, unmodified TCP receivers generate ACK trains, which carry useful information about the end-to-end link characteristics. TCP Wave inspects ACK-train flow to measure the following parameters: (i) ACK train spread (namely ACK train dispersion) and (ii) RTT variations. The former is expected to provide the overall “service capacity”, meant as the maximum capacity allowed over the end-to-end path, while the latter is considered as a congestion indicator. The joint use of such measurements allows TCP Wave to fine-tune the transmission rate to accurately match current network resource availability in the bottleneck link. This paper analysis TCP Wave ACK train-based measurements on a broad set of simulated links compliant to characteristics of today's real networks. To this scope, a testbed with TCP Wave implementation on Linux OS is used to perform tests varying both bottleneck capacity and physical latency.

In this paper we look after the secure delivery of multimedia content across an innovative Content Delivery Network comprising both satellite and terrestrial trunks. The CDN in question leverages state-of-the-art technologies both at the edges and in the core of the integrated distribution architecture and highly relies upon in-network caching strategies in order to improve its performance. We propose an architecture envisaging a combination of multicast, simulcast and unicast communication scenarios where satellite links are exploited to support local in-network caching. We analyse integrated network deployment scenarios where the satellite acts as the interconnection link between distributed in-network caches and a terrestrial CDN and/or feeds edge-network caches at micro-centre locations.

TCP Wave is an innovative transport protocol adopting a burst-based transmission approach, instead of the traditional window-based one. In TCP Wave the underlying IP packet transmission process results completely changed because of an internal timer to schedule bursts, which replaces the ACK-clocked transmission of all TCP versions. So far, TCP Wave capabilities have been assessed in a large gamut of scenarios but mainly limited to unidirectional bulk-like transfers involving a TCP sender and a TCP receiver. In this paper, TCP Wave behavior and performance are evaluated for the first time with real HTTP running applications, which are characterized by: a request/response interactive traffic model, a short and, in some cases, spaced objects transmissions and a mutual role of TCP peers that can act either as sender or receiver according to the application operations. TCP Wave procedures were accurately adapted to be suitable in this scenario and will be described in details. Finally, ns-3 simulator was setup and test campaign was performed, including both a real Web server and an HTTP client.

New paradigms for web applications have motivated in recent years a series of proposals to update the Internet protocols. One of the proposed protocols is called SPDY, endorsed and developed by Google. This protocol at application layer is able to optimize Web page loading time, allowing additional features such as multiplexing, flow control and priority, and providing security as well. Some SPDY working principles can be particularly effective in a satellite context, aspect not yet well covered by present literature. This paper assesses the use of SPDY in a satellite-based scenario, in particular focusing on the multiplexing feature, which is one of the main innovations. The main objective is to demonstrate how SPDY approach relying on few TCP connections (one in the optimal case) to carry all the Web objects brings a relevant performance improvement. The analysis is supported by experiments over a Linux based testbed introducing a long latency link to the data patch, including a reference SPDY implementation.

An efficient resource allocation is of paramount importance to guarantee the best performance with a fair distribution of satellite capacity, even for Multi-beam High Throughput Satellites (HTS) platforms. These platforms are recently gaining relevance for broadband Internet access and are nowadays able to provide xDSL like services. Although the available bandwidth for HTS is greater than previous platforms, it is still fundamental to use it wisely and avoiding abuses, which may jeopardize the service performance of the installed user-base. This paper focuses on the commercial system using the KA-SAT platform by Eutelsat, where a Deep Packet Inspection (DPI) solution is adopted to allow multi-dimensional per-user and per-application priority. Simulation and emulation tests have been executed to identify both the optimal DPI configuration and the amount of satellite capacity to procure in order to meet user requirements. Test achievements are then used to provide useful inputs for the real platform configuration in the frame of the Lift Off ESA project.

SPDY is a recent Web technology aimed to improve webpages load time and resource utilization, through the implementation of: multiplexing and prioritization of webpage objects, header compression, resource pushing and encryption. Most of these techniques are already implemented in Performance Enhancing Proxies (PEPs), which are adopted in geostationary satellite systems to optimize TCP-based application performance. Thus, SPDY is expected to provide benefits for satellite communications resource management. This paper provides a careful assessment of SPDY performance over satellite links, compliant to DVB-RCS standard, with return link resources assigned on demand through a Demand Assignment Multiple Access (DAMA) method. Such a reference scenario constitutes a challenging communication environment due to both the limited return link bandwidth and the relatively high latency. Performance evaluation has been carried out through a satellite network emulator, which reproduces physical layer satellite impairments, while running real implementations of both TCP/IP stack and SPDY.

TCP Noordwijk manages very efficiently Internet traffic when a satellite link is included in the path. The improvement of the bandwidth estimator can further increase performance, especially in presence of competing traffic using other TCP protocols, and the exploitation of innovative service paradigms, first of all, cloud computing. In this respect, a meaningful increase of data transfers with different requirements in terms of size and interactivity will be experienced and large bulk data transfers can imply congestion on the bottleneck link of the core networks, impairing performance of real-time data transfers. This issue is further emphasized when a satellite link is included on the path, since resources are limited and the large latency affects congestion recovery mechanisms. Flow control differentiation capability can be the solution to exploit cloud computing efficiently. In this paper, we propose to manage flows priority at the transport layer introducing a proxy agent installed before each satellite terminal exploiting cloud computing service, which can use different transport protocols and parameters according to the flow priority. The proxy includes the new TCP Noordwijk+ (TCPN+), which allows establishing efficient transfer of low-priority bulk data along with efficient handling of interactive data, keeping a degree of friendliness with existing standard TCP connections. The results, outcome of Ns-2 simulation, confirm the efficiency of the proposed solution.

DVB-S/S2 is used to provide multimedia broadcasting and unidirectional IP based services over satellite networks, while DVB-RCS enhances transmission in a bidirectional way, enabling transmission over the satellite return channel. Streaming Encapsulation (GSE) protocols are defined to transport 'P datagrams over DVB. They provide several benefits over Multiprotocol Encapsulation (MPE), typically used in DVB for transporting 'P data. While the security mechanism defined within DVB-RCS standard supports MPE encapsulation, there is no identified security mechanism for both ULE and GSE protocols. This paper proposes an enhanced security framework for DVBRCS security specifications adopting ULE encapsulation to provide secure lightweight encapsulation.

ESA Satlabs proposed a splitting architecture, named Interoperable-Performance Enhancing Proxy (I-PEP), which defines a protocol stack for the edges of a Digital Video Broadcasting-Return Channal over Satellite (DVB-RCS) link with the aim of improving performance of Transmission Control Protocol (TCP)-based applications. At the transport layer of I-PEPs, the Space Communications Protocols Standards-Transport Protocol (SCPS-TP) provides a reliable connection to upper layers, although resulting in very poor performance in tests. In fact, standard congestion-control mechanisms under-perform mainly due to long latency and Demand Assignment Multiple Access (DAMA) access schemes, especially in the case of short transfers, as for Web traffic, when optimum window may not be reached. In this paper, a burst-based TCP, named TCP Noordwijk (TCPN), is introduced to improve on these aspects. To evaluate performance, the protocol has been implemented on the Network Simulator NS-2. Definitively, details on the protocol design, implementation, and a vast gamut of results coming from simulations are reported.

DVB-RCS links, as well as most of VSAT systems, to improve TCP performance usually consider a PEP solution. The SatLabs group of the European Space Agency issued I-PEP, selecting SCPS-TP as transport protocol, which supports two congestion control schemes: TCP Vegas (default) and van Jacobson's Slow Start and Congestion Avoidance. In both cases the most popular TCP-based applications, i.e. Web browsing and e-mail, achieve very poor performance especially when DAMA schemes run at the MAC layer. In this frame, TCP Noordwijk has been specifically designed to optimize performance of short TCP- based data transfers over DVB-RCS DAMA links, meeting the requirement to be compatible with I-PEP specifications. This paper presents an overview of TCP-based application criticalities over DVB-RCS links and shows how TCP Noordwijk improves performance.

In a mobile communication scenario handover functions must be supported in order to keep connection alive while switching between different points of access. Moreover, if the infrastructure is composed of different networks or technologies, intersegment handover is necessary to roam from a component to another. The handover function is implemented either for necessity or to improve performance. Necessity means that the terminal must perform a handover because its current network connection is worsening; in the other case switching to another network can help to achieve better performance even if the current network connection is fine. Furthermore, the handover can be soft or hard, according to the possible overlap in the connection of the two segments involved. This paper illustrates the behavior of TCP during intersegment handovers in an architecture including two segments: satellite and WLAN. In particular, the goal is to carry out a thorough analysis of a cross-layer based mechanism applicable during handovers to optimize the TCP performance. Such a mechanism is validated with an ad-hoc software simulator written in C++ and the most meaningful results are shown.

The integration of a satellite system with a HAPS segment appears very suitable to provide communication services, including Internet access, for a large set of applications. In fact, the satellite capability to provide wide coverage and broadband access can be enhanced by the use of cost-effective, mobile/portable and low-power consuming user terminals, when HAPS acts as an intermediate repeater. Moreover, also TCP-based applications, which suffer from long latency introduced by the satellite link and in general by errors, can get benefits in terms of end-to-end performance. In this frame, this paper deals with the introduction, on board the HAPS, of an efficient CAC scheme in order to guarantee an optimal utilization of the precious radio resources. In particular, we propose an innovative TCP driven CAC algorithm, which shall take into account not only the QoS requirements, but also TCP statistics obtained through a proxy installed on the HAPS. Results show that the overall system performance in terms of both average throughput and blocking probability is significantly improved.