On Securing Real-Time Speech Transmission over the Internet: An Experimental Study
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On Securing Real-Time Speech Transmission over the Internet: An Experimental Study Alessandro Aldini Instituto di Scienze e Tecnologie dell’Informazione (STI), Universit`a degli Studi di Urbino, 61029 Urbino, Italy Email: [email protected]
Marco Roccetti Dipartimento di Scienze dell’Informazione, Universit`a di Bologna, 40127 Bologna, Italy Email: [email protected]
Roberto Gorrieri Dipartimento di Scienze dell’Informazione, Universit`a di Bologna, 40127 Bologna, Italy Email: [email protected] Received 27 May 2002 and in revised form 3 January 2003 We analyze and compare several soft real-time applications designed for the secure transmission of packetized audio over the Internet. The main metrics we consider for the purposes of our analysis are (i) the computational load due to the coding/decoding phases, and (ii) the computational overhead of the encryption/decryption activities, carried out by the audio tools of interest. The main result we present is that an appropriate degree of security may be guaranteed to real-time audio communications at a negligible computational cost if the adopted security strategies are integrated together with the playout control mechanism incorporated in the audio tools. Keywords and phrases: Internet, multimedia applications, real time, security.
1.
INTRODUCTION
The Internet offers a best-effort service over public networks without security guarantees. Therefore, the provision of secure real-time audio applications over wide area networks (WAN) like the Internet has to be carefully addressed. In particular, the success of such applications depends strictly on the speech quality and the privacy guaranteed by the provided services, which have to be perceived as sufficiently good by their users. Based on these considerations, we concentrate our attention on the steps of the audio data flow pipeline (depicted in Figure 1) which affect the performance and the security features of those applications designed for delivering secure real-time communications over the Internet. More precisely, in this paper, we analyse several audio applications to investigate the overhead, in terms of additional latency, which is caused by the embedded data compression algorithms and securing mechanisms. In general, the provision of both adequate performance and security for the above-mentioned applications has to be carefully examined and modeled because of some important constricting conditions, illustrated as follows.
(i) These applications are often constrained to work under very restrictive resources (e.g., bandwidth) and congested traffic conditions. In particular, network-based audio applications experience variable transmission delay; hence the most used approach in order to ameliorate the effect of such an inevitable problem is to adapt the application behavior to the variable network delays (see, e.g., [1]). (ii) Real-time audio applications which employ public, untrusted, and uncontrolled networks have strict security requirements, namely, they have to guarantee authentication, confidentiality,
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