Voice-over-IP on RISC OS: What's involved?By Chris Williams. Published: 30th Oct 2005, 15:47:16 | Permalink | Printable
A client is possible once someone with the brains is talked into making itWith media outlets firefighting the outbreak of blogging and high street stores plotting revenge against online shops, the telecom giants thought they were safe from the Internet - some even providing the broadband and dialup connections that people use. Suddenly, however, a new technology has appeared on the radar and is threatening to torpedo the corporate strangle-hold of voice communications. Voice-over-IP allows people to chat to each other over the Internet using a microphone headset with a PC or a normal phone, and by 2010, half the UK population is expected to be using it.
Calls between VoIP users are usually free, whereas connections to external phone networks require payment as usual. The VoIP protocol works by breaking conversations up into packets of encoded data and sending them over the Internet, in the same sort of way your requests for web pages, email and other information are sent. By using this existing infrastructure, VoIP service providers can keep their costs down while providing standard features including caller display, voicemail and 1471. A number of service providers exist, the most famous being Skype.
So, on RISC OS?
At the moment, there are no VoIP clients nor any development work known to be underway for a new client. Skype uses a closed source protocol, which is a show stopper, although there are a number of open source libraries which provide VoIP functionality. The SIP Foundry is working on a number of libraries and components that could be used to make a VoIP client. These all make use of the SIP standard, which controls the flow of real-time communications. The GNU also have their own open source implementation too, and the H.323 standard is an alternative to SIP.
The audio data recorded live during conversation also needs sampling and compressing, and there are plenty of codecs available to do that - for example, G.711. This works by converting an audio stream into a digital representation at a rate of 64kbits/s. A RISC OS client would also need a way to capture audio from a microphone, and there are a number of ways to achieve this. The Iyonix's audio-in could be handy, although at the moment the software interface for this isn't flexible enough to provide a live stream. There is also the headache of maintaining real-time data streams on RISC OS, given its approach to multitasking, and having the processing power to recreate conversations - especially when packets inevitably arrive late or out of sequence. The VoIP client would, obviously, also have to decompress arriving audio data and output the sound. Developers we spoke to recently felt that a VoIP client is certainly possible, once someone finds the time to produce one.
Once all this is implemented and rolled into an application, the SIP capable client could then connect to and use any SIP compliant VoIP provider. Due to the amount of data shifted during a conversation, a broadband connection is mandatory. Consumer groups have also warned users of ISPs with 'download caps' to make sure they don't go over these limits with endless VoIP calls.
And in the meantime?
Several RISC OS users have found that plugging a phone into a VoIP capable broadband router and using a supported provider works well. RISC OS browsers, including Oregano 1 and the Firefox port, can be used to configure the kit. Vonage use SIP-compatible LinkSys routers to provide VoIP functionality, as illustrated here. A sticking point with VoIP is the issue of emergency services calls: On a normal copper telephone network, calls to 999 still work even when the electricity supply fails. VoIP users are out of luck in such situations, or if their computer hardware fails for whatever reason, although Vonage and other providers do offer a 999 service.
Gossiptel and Sipgate are also used by RISC OS users using extra equipment that provide VoIP functionality to normal phones, such as the Vigor2600V. There is a wide choice of providers and hardware in the absence of a native RISC OS client.
One user down under in Australia, Ross McGuinness, is considering using VoIP, and asked how a RISC OS client could be developed and funded. He said: "With the spread of broadband and the move away from standard copper telephone services this is the major change facing telephony.
"In my case the copper service is deteriorating and I'm awaiting a two way satellite service, shared over a radio network, with my neighbours. This service is supplied by one of the alternative telephone service operators who is also looking to expand their telephone customer base using VoIP on their broadband service. It is cheaper than building or possibly replacing a copper network in Australia's vast distances.
"With a copper cable damaged by several major lightning strikes and unlikely to be improved in the short term, if ever, I'm keen to see if VoIP can replace one of my land lines."
More on VoIP
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