1,720,974 research outputs found
PEPsal: a Performance Enhancing Proxy for TCP satellite connections
No full textInternet communications with paths that include satellite link face some peculiar challenges, due to the presence of a long propagation wireless channel. In this paper, we propose a Performance Enhancing Proxy (PEP) solution, called PEPsal, which is, to the best of the authors’ knowledge, the first open source TCP splitting solution for the GNU/Linux operating systems. PEPsal improves the performance of a TCP connection over a satellite channel making use of the TCP Hybla, a TCP enhancement for satellite networks developed by the authors. The objective of the paper is to present and evaluate the PEPsal architecture, by comparing it with end to end TCP variants (NewReno, SACK, Hybla), considering both performance and reliability issues. Performance is evaluated by making use of a testbed set up at the University of Bologna, to study advanced transport protocols and architectures for internet satellite communications. At present PEPsal is adopted, with success, by a satellite Internet provider
PEPsal: a Performance Enhancing Proxy designed for TCP satellite connections
No full textInternet communications with paths that include satellite link face some peculiar challenges, due to the presence of a long propagation wireless channel. In this paper, we propose a Performance Enhancing Proxy (PEP) solution, called PEPsal, which is, to the best of the authors' knowledge, the first open source TCP splitting solution for the GNU/Linux operating systems. PEPsal improves the performance of a TCP connection over a satellite channel making use of the TCP Hybla, a TCP enhancement for satellite networks developed by the authors. The objective of the paper is to present and evaluate the PEPsal architecture, by comparing it with end to end TCP variants (NewReno, SACK, Hybla), considering both performance and reliability issues. Performance is evaluated by making use of a testbed set up at the University of Bologna, to study advanced transport protocols and architectures for internet satellite communications
A DTN Approach to Satellite Communications
No full textSatellite communications pose serious challenges to transport layer performance, mainly because of long propagation delays (especially in geosynchronous systems) and the possible presence of random errors on the satellite link. Solutions that cope with these impairments usually rely upon either the adoption of enhanced versions of transport protocols, or the insertion of intermediate agents, like PEPs (Performance Enhancing Proxy). An alternative approach is to adopt the DTN (Delay/Disruption Tolerant Networking) architecture based on the introduction of the new “bundle” layer in the protocol stack. The aim of the paper is to discuss the advantages and disadvantages of the DTN approach compared to the more conventional solutions mentioned. DTN performance is assessed by considering both fully connected networks and networks where continuous connectivity cannot be guaranteed during data transfer and/or at start-up. Performance is evaluated by using the TATPA testbed (Testbed for Advanced Transport Protocols and Architectures), which is based on a cluster of Linux PCs running the DTNperf application, developed to this end by the authors and now included in the official DTN package
Virtual Integrated TCP Testbed (VITT)
No full textResearch on TCP performance relies either on simulation programs, which run on a single machine, or on the use of real testbeds, where different machines represent different network nodes and data exchange is made through physical network interfaces. This paper proposes a different solution, with the aim of taking the best of both the cited alternative options. The idea is to exploit the most advanced virtualization technologies to integrate the different devices of a real testbed in a single GNU/Linux physical machine. The Virtual Integrated TCP Testbed (VITT) presented in this paper is the practical realization of this concept. Several virtual machines, fully configurable from the host system, are connected through an emulated network, implemented by means of the software tools provided by the Virtual Distributed Ethernet (VDE) project. A simple web interface allows the user to configure the network layout, set the TCP parameters, launch the experiments and gather the results. VITT is built on the experience achieved by the authors in the design and use of a real distributed testbed (TATPA), from which VITT derives some software components. TATPA results proved essential to assess the present limits of the virtualization approach, i.e. the accuracy of results vs. network complexity
The "TCP Adaptive-Selection" Concept
No full textThe rapidly increasing importance of wireless communications
(including satellite), together with the rapid growth
of high speed networks, pose new challenges to transmission control
protocol (TCP). Among them, the most prominent are long
round trip times (RTTs), not negligible packet error rates (PER),
and very large bandwidths. To overcome them, a wide variety of
TCP enhancements has been presented in the literature with different
purposes and capabilities. However, as most proposals aim
to address different impairments, they result optimized for specific
network environments. Therefore, given the increasing level of heterogeneity
of present and future networks, the choice of “the best”
TCP enhancement seems a quite irresolvable problem, depending
on the characteristics of the specific connections. The TCP adaptive-
selection concept, presented and discussed in this paper, aims
to circumvent this problem by providing an alternative approach
that challenges at the root the idea that only one TCP enhancement
must be adopted, not only on the whole network in general, but
also on the same server machine. In fact, by extending the concept
that underlies adaptive coding and modulation (ACM) to transport
layer, TCP adaptive-selection envisages the concurrent adoption
of different TCP versions on the same server, the better to
match the different impairments present on different connections.
The implication of this novel approach, as well as the possible criteria
to be adopted for the TCP selection, are deeply discussed in
this paper, where a particular emphasis is given to the “dynamic”
TCP adaptive-selection variant. Preliminary results, referring to
a simple network topology, chosen to enlighten the mechanism of
the TCP adaptive-selection technique, are also provided. They are
quite encouraging and justify the following remarks on feasibility
and the discussion of some implementation proposals
An emulation approach for the evaluation of enhanced transport protocols performance in satellite networks
No full textTo overcome the unsatisfactory performance offered by standard TCP variants in the challenging satellite environment, the scientific community has presented a wide variety of possible solutions, encompassing both innovative transport protocols and architectures. Among these, the paper focuses on those TCP variants that have been actually implemented in real operating systems and in Linux in particular. The aim of the paper is to present a sound emulation approach for their performance assessment. This approach relies on the set-up of a complete testbed, able to reproduce, in a fully controlled (“clean”) environment, the characteristics of satellites networks, and to provide “live” data from actual implementations of TCP variants. After validating this approach by means of ns-2 results comparison (when available), the paper presents the results of a complete series of tests, which are proposed by the authors as significant elements for a possible future common evaluation benchmark
TCP, PEP and DTN Performance on Disruptive Satellite Channels
No full textFixed GEO satellite communications are impaired by long RTTs and the possible presence of packet losses on the satellite radio channel. Moreover, when the satellite receiver is mobile, short and long disruptions due to line of sight obstructions can cause further performance deterioration. In this paper, we present a preliminary assessment of disruption impact on performance comparing different approaches, such as end-to-end TCP, PEP based on TCP splitting and DTN. Performance is evaluated on a Linux testbed, by emulating the satellite link interruptions caused by tunnels on a real railway line. Results show that good performance can be achieved by all of the approaches considered provided that on the satellite channel an efficient TCP variant, like Hybla, is adopted; however, DTN offers best performance. DTN superiority emerges when the disrupted satellite channel is the last leg of a congested path, thanks to the DTN custody transfer mechanism and store and forward capability
Virtualization Technologies for DTN testbeds
No full textAt present, Internet is based on the availability of a continuous path from the source to the sink node and on limited delays. These assumptions do not hold in “challenged networks”, which comprise a wide variety of different environments, from sensor networks to space communications (including satellite systems). These networks are the preferred target of Delay/Disruption Tolerant Networking (DTN), an innovative networking architecture able to cope with long delays, channel disruptions and limited or intermittent connectivity. Given the increasing interest in DTN, there is urgent need for suitable tools for DTN performance evaluation. In general, there are two approaches to performance evaluation in networking: simulation and real testbeds. In this paper, after an in-depth discussion of advantages and disadvantages of both, a third way based on a virtualization is proposed and tested for DTN environments, for which it seems particularly suitable. To validate this assumption, a virtual counterpart of a real testbed is set-up using Virtual Testbed Toolkit (VTT) components. A series of tests is then performed by considering DTN transmission on a heterogeneous network including a GEO satellite link. The close match between real and virtual testbed results confirms the validity of the virtual approach for accurate performance evaluations in DTN environments
DTN meets smartphones: future prospects and tests
No full textAlthough first conceived for the Interplanetary Internet, DTN (Delay-/Disruption-Tolerant Networking) architecture has successively enlarged its application scope to embrace all “challenged networks”, i.e. networks where the TCP design key assumptions of short RTT, no disruptions, and continuous end-to-end path availability are challenged. The distinctive features of DTN architecture seem ideal for the connectivity problems of modern smartphones. These are both PCs and cell phones and are characterized by a wide range of different communications technologies, including Bluetooth, WiFi, and advanced 3G radio interfaces, like UMTS HSPA (High-Speed Packet Access). The aim of this paper is to show that it is both feasible and useful to adopt DTN architecture on these advanced devices, in addition to the usual TCP/IP protocol stack. To this end, a series of tests is presented and discussed in the paper, considering various communication interfaces, 3G in particular. Tests were greatly facilitated by the introduction onto the market of some smartphones running Linux based operating systems, like Maemo, which allowed the authors the direct use of “official” DTN code (i.e. the DTN2 reference implementation and the DTNperf_2 evaluation tool)
A DTN Approach to Satellite Communications
No full textSatellite communications pose serious challenges to transport layer performance, mainly because of long propagation delays (especially in geosynchronous systems) and the possible presence of random errors on the satellite link. Solutions that cope with these impairments usually rely upon either the adoption of enhanced versions of transport protocols, or the insertion of intermediate agents, like PEPs (Performance Enhancing Proxy). An alternative approach is to adopt DTN (Delay/Disruption Tolerant Network) architecture, based on the introduction of the new “bundle” layer in the protocol stack. The aim of the paper is to discuss the advantages and disadvantages of the DTN approach compared to more conventional solutions. DTN performance is assessed by using a testbed based on a cluster of Linux PCs running the DTNperf application, which was developed to this end by the authors and now included in the official DTN package. Preliminary results are presented and discussed in the paper
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