The least expensive VoIP solution would be using a computer on a peer to peer network. Offered from such VoIP service providers as Skype or the Gizmo Project, the software is free to download and calls within the network are free worldwide. Calls to PSTN numbers are charged at a low VoIP rate, and in the case of Skype, at a low yearly rate. Peer to Peer VoIP is a software solution, meaning that no ATA is required, and your phone is a pair of earplugs and a microphone plugged into your computer. The downside is that call quality is lacking compared to some of the hardware VoIP solutions available.



Establishing a Peer-to-Peer VoIP Call

A peer-to-peer VoIP call occurs when two VoIP phones communicate directly over IP without IP PBXs between them. A peer-to-peer call can be initiated directly, by calling a phone’s SIP URI, or indirectly by dialing a phone number. A peer-to-peer call will only be established when a phone number is dialed if both phones share an IP PBX. For an audio call, there is no difference (in end user experience) between a peer-to-peer call and one that uses an IP PBX.

However, peer-to-peer calls become important if callers use features like push-to-talk, video, and mesh-based audio conferencing. The VoIP versions of these features cannot be transmitted over PSTN. The features can only be used in peer-to-peer VoIP calls.

VoIP has been called a few different things in its colourful past such as internet telephony, peer-to-peer, P2P, IP telephony, broadband telephony, voice over broadband and many, many other names. At Skype we much prefer using the simpler term free calls over the internet than the geeky VoIP.


Another Skype competitor

Here is another competitor to Skype in the peer to peer VoIP world -- called Peerio it appears to have a number of advantages over Skype... with a few caveats though.

An Experimental Study of the Skype Peer-to-Peer VoIP System

Skype's peer-to-peer overlay, and the network workload generated by Skype users. Third, we provide data on user-behavior that can be used for future design and modeling of peer-to-peer VoIP networks; note that developing an explicit quantitative model is out of scope of the present paper. Altogether, we find evidence that Skype is fundamentally different from the peer-to-peer networks studied in the past.Supernode-based peer-to-peer networks organize participants into two layers: supernodes, and ordinary nodes. Such networks have been the subject of recent research in [29, 28, 6, 5]. Typically, supernodes maintain an overlay network among themselves, while ordinary nodes pick one (or a small number of) supernodes to associate with; supernodes also function as ordinary nodes and are elected from amongst them based on some criteria. Ordinary nodes issue queries through the supernode(s) they are associated with.Many peer-to-peer networks handle churn by dynamically restructuring the network through periodic or reactive maintenance traffic. Churn has been studied extensively in peer-to-peer file-sharing networks [26, 27, 2, 13, 7]; the consensus is that churn can be high.

Future Work
We have only scratched the surface of understanding how peer-to-peer supports VoIP. More generally, interactive applications such as peer-to-peer web-caching, VoIP, instant messaging, games etc. may demonstrate different characteristics than P2P file-sharing networks and we are interested in understanding these differences. Measuring existing interactive networks including instant messaging networks (AIM, MSN, Yahoo!) and massively multiplayer game networks (World of Warcraft, Ultima Online) can reveal different user behavior. In addition, it would be useful to compare user experience, call setup latency and call quality in Skype and other infrastructure-based telephony services including traditional telephone and cellular networks, and VoIP networks that use SIP and H.323 for signaling. Combined, these would give insights about how peer-to-peer networks for such applications should be built and provisioned.

Overall, we present measurement data useful for designing and modeling a peer-to-peer VoIP system. Even though this data is limited due to the proprietary nature of Skype, we believe that this study could server as a basis for further understanding and discussing the differences between peer-to-peer file-sharing and peer-to-peer VoIP systems.


VoIP Technology for SIP Peer-To-Peer :

Fusion believes its new "efonica" branded softphone and uniquely configured VoIP network will provide significant advantages over most VoIP peer-to-peer networks. Fusion's technology eliminates the method of routing utilized by many VoIP peer-to-peer networks, in which many users' Internet bandwidth and/or PCs are utilized as part of the carrier's larger network to set up calls for thousands of other users. DSP technology for peer-to-peer Internet calls is one of several differentiators behind Fusion's new VoIP offering, expected to be launched worldwide this quarter", remarked Matthew Rosen, Fusion's President and CEO.











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I saw a demo of another enterprise peer-to-peer system in UK recently- from a Canadian company called Nimcat Networks. Awesome. They are backed by some big players. I think peer-to-peer is the future of business VoIP.