R. Secchi - Academia.edu (original) (raw)

Papers by R. Secchi

2005 Symposium on Applications and the Internet Workshops (SAINT 2005 Workshops), 2005

In this paper, we evaluate the performance achieved by DWRR and WFQ, the widespread implementatio... more In this paper, we evaluate the performance achieved by DWRR and WFQ, the widespread implementations of frame-based and sorted-priority schedulers respectively, in a high speed DiffServ environment. Using deterministic upper bounds of the end-to-end delay, we evaluate the schedulers behavior for a wide range of bandwidth configurations. Our analysis highlights the drawbacks of using frame-based scheduling with respect to sorted-priority when dealing with multiple classes of service. As a consequence, we propose a configuration of scheduler weights, which allows to contain the loss in performance of framebased schemes, while minimizing the end-to-end delay for premium classes. Extensive simulations confirm our theoretical propositions and show the effectiveness of our method in satisfying hard quality of service requirements even in highly congested networks.

Advanced Industrial Conference on Telecommunications/Service Assurance with Partial and Intermittent Resources Conference/E-Learning on Telecommunications Workshop (AICT/SAPIR/ELETE'05), 2005

Computer-based learning environments provide the opportunity to promote students interactivity an... more Computer-based learning environments provide the opportunity to promote students interactivity and meet their individual needs. Because of the advantages of such approach, the computer-based teaching is becoming very popular in universities and in other educational institutes. However, very often the solutions proposed to support the educational activities are not inter-operable and lack of a suitable network infrastructure. In this paper, we report the results of several teaching experiences gathered from more than one year of activities in various research projects. Our first step has been the development of a platform able to fully integrate the new powerful teaching tools, such as the virtual blackboard, and network transport services. From these experiences, we realized that the learning quality would be improved if students interactively participate to the learning process. Then, in a later experimentation, we proposed and validated a model of e-classroom, which would guarantee the mobility to students and preserve their identity. We show that this kind of mobile-learning is only possible whereas an advanced networking technology, such as Mobile IPv6, is enabled.

IEEE International Conference on Communications, 2005. ICC 2005. 2005, 2005

This paper presents a simulative analysis of a modification to the TCP congestion control mechani... more This paper presents a simulative analysis of a modification to the TCP congestion control mechanism called ESSE (Early Slow Start Exit), designed to improve the TCP startup phase by setting the slow start threshold according to a pipesize estimation based on the observation of few ACK arrival times. We evaluate the performance of ESSE by using various methods to estimate the pipesize as the ratio between the round trip time and the spacing between ACKs. This algorithm is easy to implement and preserves the compatibility with the standard protocol since it requires changes to the sender side only.

Proceeding from the 2006 workshop on ns-2: the IP network simulator - WNS2 '06, 2006

2006 International Workshop on Satellite and Space Communications, 2006

Satellite systems are evolving towards higher available bandwidths and dynamic allocation based o... more Satellite systems are evolving towards higher available bandwidths and dynamic allocation based on instantaneous traffic rates offered at the stations, so called BoD (bandwidth on demand) channel sharing. This trend is paired with more and more powerful error correcting schemes, like those adopted in the recent DVB-S2 standard, which promise to make the channel virtually immune from packet errors. These factors, together with the significant round-trip delay of geostationary satellites, combine so that most TCP connections would send all of their data during the Slow Start phase. We investigate the performance of TCP during startup on recent BoD system by observing and explaining the behavior of different TCP flavors on different systems when transmitting data over the Eutelsat's Skyplex Data satellite system. We make recommendations for choosing and improving TCP implementations and for future BoD allocation schemes.

Lecture Notes in Computer Science, 2003

In this paper, we propose a novel bandwidth estimation algorithm for TCP connections and its poss... more In this paper, we propose a novel bandwidth estimation algorithm for TCP connections and its possible application to congestion control mechanism. The estimation algorithm relies upon an analytic relation which expresses the connections' available bandwidth as a function of the inter-departure time of packets and of the inter-arrival time of ACKs. It is worth noticing that this approach can be extended to protocols other than TCP, as long as they support an acknowledgment mechanism. The bandwidth estimation performance is assessed through discrete event simulations under various network topologies, traffic scenarios and link error conditions. Bandwidth estimation is then applied to TCP congestion control to select the value of the congestion window after a packet loss episode. Performance of this modified version of TCP is validated by means of simulations and compared to the one achieved by TCP NewReno. Finally, the possible coexistence of the modified version of TCP and TCP Ne-wReno is proved through a detailed analysis of fairness and friendliness of the new protocol.

Lecture Notes of the Institute for Computer Sciences, Social Informatics and Telecommunications Engineering, 2013

Satellite is considered a vital technology for enabling ubiquitous access to broadband services i... more Satellite is considered a vital technology for enabling ubiquitous access to broadband services in many countries. This paper explores provision of IP-based broadband satellite access with Quality of Service (QoS). It analyses a set of example scenarios, based on the recently published DVB-RCS2 standard involving web and voice traffic. It specifically explores the interaction between Bandwidth-on-Demand (BoD) and QoS, showing that this interaction offers the flexibility required for satellite Internet service operators to manage the bandwidth of broadband users in a multi-service access network.

2013 IEEE Symposium on Computers and Communications (ISCC), 2013

Many modern Internet applications require fast client-server interaction to maximise user interac... more Many modern Internet applications require fast client-server interaction to maximise user interactivity. This need has caused new work to be proposed to working groups of the Internet Engineering Task Force (IETF), which seek to remove bottlenecks when starting sessions. RFC 6298 improves Transmission Control Protocol (TCP) responsiveness by retransmitting lost SYNs, or first data segments sent after the three-way handshake (3WHS), with a reduced initial retransmission timeout (RTO) of 1 second from the previous value of 3 seconds. This benefits a large number of Internet connections. However, there is growing use of wireless and other long-haul radio technologies that yield round trip times (RTT) greater than 1 second. This means a significant number of connections will suffer spurious retransmissions with associated performance penalties. This paper examines whether RFC 6298 can cooperate with a set of proposed methods to extend performance benefits to long delay paths that may experience startup loss. It was found that a slight modification of TCP congestion-state initialization after the 3WHS significantly improves performance, especially if combined with SYN duplication and an increased Initial Window (IW). We further explain how a deprecated proposal to seed the RTO based on the SYN round trip time (RTT) can be updated to become suited for general deployment. Proposed modifications are evaluated, by analysis and using ns2 simulations, showing improved overall responsiveness for short delay paths as well as networks paths with shared bandwidth and appreciable delay (e.g. wireless/satellite networks).

Proceedings of Network and Operating System Support on Digital Audio and Video Workshop - NOSSDAV '14, 2013

ABSTRACT A recent proposed update to TCP congestion control, TCP-newCWV, has targeted congestion ... more ABSTRACT A recent proposed update to TCP congestion control, TCP-newCWV, has targeted congestion control for rate-limited applications. These methods need to be explored in the context of rate-adaptive applications, such as DASH. The new method enables a client to exploit the persistence of a DASH connection and enables the DASH server to rapidly resume transmission of a series of video segments using a single TCP connection. Another technique, called 'Pacing' smoothes DASH bursts when there is no TCP ACK clock, and is shown to significantly reduce burst loss. These two methods in combination can increase the application performance. This paper investigates the effect of implementing these techniques on a DASH flow in different congestion scenarios and whether the method can promote better capacity sharing while minimizing the latency experienced by other flows sharing a common network bottleneck. The results confirm that newCWV with Pacing provides a benefit as a platform for DASH transport.

2008 IEEE International Workshop on Satellite and Space Communications, 2008

We discuss in this paper basic requirements of an RCST gateway supporting VoIP traffic without st... more We discuss in this paper basic requirements of an RCST gateway supporting VoIP traffic without strict QoS provisioning. Besides easing the system design, a QoS management not based on reservation is suitable to accomplish changes in traffic scenarios and to support new applications. The main elements of this architecture are illustrated throughout the paper following a layered structure. A preliminary set of simulations is presented to point out benefits and to identify major issues. Implications of buffer management, different scheduling algorithms, and bandwidth allocation protocols are analysed.

31st AIAA International Communications Satellite Systems Conference, 2013

International Journal of Satellite Communications and Networking, 2009

In the not so distant future, we envisage an Internet where the biggest share of capacity is used... more In the not so distant future, we envisage an Internet where the biggest share of capacity is used by streaming applications. To avoid congestion collapse from unresponsive flows calls for a robust and ubiquitous end-to-end multimedia congestion control mechanism, such as TCP-friendly rate control (TFRC), which provides fair sharing with the other Internet traffic. This paper therefore analyses the implications of using rate-adaptive congestion control over satellite links that utilize demand allocation multiple access (DAMA) to maximize satellite transponder utilization. The interaction between TFRC and DAMA is explored using simulations supported by fluidic flow models. The analysis shows that DAMA slows down the start-up phase of TFRC, causing non-negligible delays. To mitigate this problem, we propose a new cross-layer method based on the Quick-Start mechanism. This can accelerate the start-up of multimedia flows by a judicious allocation of additional capacity derived from cross-layer signalling.

IET Communications, 2010

The real-time control of multiple queues handling traffic of different nature is obtaining increa... more The real-time control of multiple queues handling traffic of different nature is obtaining increasing relevance in both the uplink and downlink of wireless telecommunication networks, characterised by the presence of a central access point. Such is the case of satellite networks, with either on-board processing or double-hop configuration, besides a number of terrestrial local and metropolitan wireless networks. Given a certain amount of available bandwidth, the problem is that of deciding, within a certain time frame, the allocation of bandwidth partitions for each traffic queue, whose packets are awaiting transmission; eventually, this determines the transmission rates to be passed to the scheduler and to the physical layer adaptive coding and modulation devices. In a satellite network, where this task is accomplished by a master station, residing at the access point, it is possible to take such decisions by means of a centralised controller, based on real-time instantaneous (in the downstream direction) or delayed (in the upstream) information on the queues' state. The study derives a control law to be used in this task, by adopting an approach based on optimal linear quadratic regulation. Both cases of un-delayed and delayed information are considered. The control laws are tested in a geo-stationary satellite scenario of digital video broadcasting -return channel via satellite (DVB-RCS), and the queues are considered at the medium access control level. Simulation results under real-traffic traces are also presented to highlight the effectiveness of the control and to compare alternative solutions.

IEEE Transactions on Vehicular Technology, 2000

The problem of optimizing access and bandwidth sharing among Transmission Control Protocol (TCP) ... more The problem of optimizing access and bandwidth sharing among Transmission Control Protocol (TCP) connections in the mobile digital video broadcasting return channel via satellite (DVB-RCS) is tackled in this paper. After sketching the general system architecture, we explicitly deal with the dynamic assignment of bandwidth to TCP connections on the return link, which is accomplished by a network control center (NCC) placed onboard the satellite. Mobile users access the satellite in multifrequency time-division multiple access (MF-TDMA), whereas they receive data from the NCC in time-division multiplexing (TDM). Two different techniques, based on deterministic and random access, are compared in terms of bandwidth usage and average completion time per connection, when the mobile user acts as both server and client. In the server case, to increase the TCP throughput, both packet-level forward error correction (FEC) on data sent by mobile users and a duplicated and delayed acknowledgment technique for TCP acknowledgment traffic from the NCC to the mobile users are applied. An analysis of the packet losses and a simulation campaign of file transfers by employing a realistic channel model has been carried out. The results of the analysis show the convenience of adopting a technique, in addition to the optimal data redundancy in different cases, such as the server or client role of users, their willingness to pay, the file size, and the environment type.

Since satellite networks provide a valuable bandwidth access to vast regions at relatively low co... more Since satellite networks provide a valuable bandwidth access to vast regions at relatively low costs, recently the interest in Internet access through satellite links has considerably increased. At the same time, the TCP/IP protocols suite is widely used in all the communication environments, encompassing the most important network applications. Thus, the actual exploitation of satellite technology into the global Internet is possible only by moulding satellite access control scheme to the TCP/IP network features. Starting from a set of measurements carried out in a DVB-RCS network, in this paper we propose an analytical model of the RBDC medium access control scheme. The model highlights how bandwidth-on-demand allocation mechanisms may lead to large packet delivery delays when sudden variations in the incoming traffic rate, typical of multimedia traffic flows, occur. Due to the effectiveness of the model, it is possible to use it for improving resources allocation strategies.

Page 1. A Simple Markovian Model of TCP Startup Behavior (Extended Abstract) Stefano Giordano,Mic... more Page 1. A Simple Markovian Model of TCP Startup Behavior (Extended Abstract) Stefano Giordano,Michele Pagano, Gregorio Procissi, Raffaello Secchi ... References [1] L. Guo and I. Matta. The War Between Mice and Elephants. In procedings of ICNP'01, November,2001. ...