A Delay Tolerant Platform for Voice Message Delivery Costas Tziouvas, Lambros Lambrinos Dept. of Communication and Internet Studies Cyprus University of Technology Limassol, Cyprus {costas.tziouvas, lambros.lambrinos}@cut.ac.cy Chrysostomos Chrysostomou Frederick University Nicosia, Cyprus ch.chrysostomou@frederick.ac.cy Abstract - A voice conversation is predominantly known as a synchronous, delay intolerant form of communication. To complement voice conversations, voice messaging is a form of asynchronous communication used when the called party is unavailable; a delay in message delivery is naturally expected and tolerated. To this extent, a Delay Tolerant Network can be utilized as the underlying data transport mechanism for the delivery of voice messages and in this paper we describe an architecture that combines this technology with the functionality of Voice-over-IP based systems. Our target application concerns the delivery of voice messages that originate from IP-based systems and are destined either for users of other IP-based systems or the Public Switched Telephone Network. Keywords: Delay Tolerant Network, voice message, VoIP, SIP I. INTRODUCTION Even in today’s modern era where text messaging is the predominant way of exchanging small ‘pieces’ of information, voice messaging is still popular owing to its more personal touch and relative ease of use. Due to the fact that an immediate response (if any) is usually not expected, voice messaging can be considered as an asynchronous form of communication. In a fashion similar to email, the sender of the message does not know when the intended recipient will actually receive the message; the message can be stored on an answering machine for minutes, hours or even days. In addition to the analogue and mobile telephony world, voice messaging is also used in VoIP-based (i.e. packet switched) systems, where the system can also be configured to send the message as an email attachment to the user associated with the number called; this is primarily done in order to expedite delivery of the message (e.g. the user is not near his/her phone but has email access) but the email may also not be readily accessible. Based on the above and due to its delay tolerance, voice messaging is perfectly suitable for networks with intermittent connectivity. An intermediary gateway is often used to interconnect VoIP systems to the Public Switched Telephone Network (PSTN). In areas where connectivity occurs opportunistically or resources (e.g. telephone lines) are limited, it may not always be possible to place outbound calls and talk to the other party; in such a case, we propose that the caller leaves a message instead. Note that our target application is slightly different than traditional voice messaging where messages are stored immediately at the recipient’s voice mail box and access time depends solely on the recipient; we have another inherent delay due to the frequent delivery network disconnectivity but at least, a messaging service is provided where it would not normally be possible. In the architecture proposed in this paper it is assumed that when a call is placed, an end-to-end path from caller to recipient does not exist and a voice message will be left. Using delay tolerant network mechanisms, the voice message will eventually reach a system that can deliver it to its recipient. In our work, in addition to an underlying DTN architecture, we utilize an IP-PBX for call management, voicemail creation and PSTN gateway access. In the following sections of this paper, we first give an overview of related technologies and then present our system architecture, its components and their functionality. Finally, we discuss our conclusions and plans for future work. II. BACKGROUND In this section we briefly present some background information on the technology and the tools our work is based upon. A. Delay Tolerant Networking (DTN) In order to facilitate communication between nodes residing in networks where some fundamental assumptions required for TCP/IP to work properly are not valid, researchers proposed [1] Delay Tolerant Networking (DTN). A DTN can be implemented in the form of a network overlay [2] that delivers packets using asynchronous message forwarding. It is designed to operate in environments with limited expectations of end-to- end connectivity and node resources; to this extent, it was initially proposed to facilitate interplanetary communication but as we will see it has also been useful in other applications.