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EarthLink Intros SIP-Based P2P Prototype

Officials at EarthLink's R&D facility have quietly released a proof-of-concept file-sharing application based on the Session Initiated Protocol .

SIPshare, written by EarthLink R&D staff and released to the open source community on its R&D discussion forum late Wednesday, demonstrates the viability of SIP as a protocol over which peer-to-peer (P2P) applications may be implemented beyond voice and video cases.

SIP is an IETF standard for initiating an interactive user session that involves multimedia elements, such as video, voice, chat and gaming. It is mostly used to power Voice over IP applications, but EarthLink's researchers believe implementations can be extended to P2P applications for enterprise use.

The R&D unit said SIPshare includes features for peer discovery, content search, file transfer and downloading using SIP messaging.

For example, content searches are passed from one peer to all other known peers, which allows content to be located on a host that the original requesting peer is not aware of. Once the content is located, it uses the SIP Invite feature to request the content from the known host.

Another feature, the distributed content search tool, lets users share documents, photos and other files via SIP and a UDP-based file transfer protocol. The UDP protocol offers a direct way to send and receive broadcast messages over an IP network.

According to Mark Petrovic, EarthLink vice president of R&D, the ISP wrote it to convince themselves and others that modern P2P applications can be written on top of SIP. In his note, Petrovic made it clear the SIPshare application was "alpha code at best" and warned that it should not be used for mission-critical applications.

"Feel free to extend it, modify it," he said. "But we do not advise using it for anything that matters."

EarthLink said a belief that "an open Internet is a good Internet," motivated the release of the P2P prototype.

"An open Internet means users have full end-to-end connectivity to say to each other whatever it is they say, be that voice, video, or other data exchanges, without the help of mediating servers in the middle whenever possible," the company said. "We believe that if peer-to-peer flourishes, the Internet flourishes. SIPshare helps spread the word that SIP is [much more] than a powerful voice over IP enabler."

This is not the first time that SIP has been associated with the peer-to-peer concept. A P2P infrastructure is being used to handle IP-based phone calls on Skype, which is a Net phone service launched by the founders of Kazaa.

However, EarthLink's researchers believe SIPshare differs from Skype because it uses standards-based protocols to handle content sharing.

"The emerging ubiquity of SIP as a general session-initiation enabler provides a rare opportunity to offer users all manner of P2P applications over a common protocol, instead of inventing a new protocol for each new P2P application that comes along," the ISP argued.

"EarthLink wants to point the way and aid the cause of these new applications by demonstrating in open source working code that SIP can host powerful applications beyond those that immediately come to mind, that is, voice and video," the company added.

It is written for Java 2 Standard Edition (J2SE) and runs on any platform for which a J2SE virtual machine is available, including Windows, Linux, Mac OS X and Solaris.

The company said SIPshare is not a supported EarthLink product.