VoIP call transfer?

Matthew S. Hamrick mhamrick at cryptonomicon.net
Thu Mar 29 00:08:28 CEST 2007

Matthew... what you're describing is sometimes called "Fixed Mobile  
Convergence." Or rather, the "FMC" term has grown to encompass the  
scenario you describe.

I use Skype on a HTC Apache (or is it the Wizard?) with EVDO and  
voice from Verizon. Honestly, I'm surprised Verizon lets me get away  
with this. This is the type of thing I would think they would want to  
shut down. I've tried Skype on a Mac over Blooteuth over EDGE, too,  
and it's not completely bad. There's a delay that ranges from 350  
msec to well over 2 seconds, but the median seems to be somewhere  
around 500 msec. Not completely bad, but it leaves you wanting  
something better. What I've noticed about EVDO is that throughput  
falls through the floor when you're on the move. EDGE seems to suffer  
this effect much less, but on both technologies, it's definitely  

So... from a network perspective, there may be some issues with  
latency and maintaining throughput as you're driving.

 From an application perspective, I have a contact at eBay labs who's  
been pressuring the Skype team to release an ARM/Linux binary.  
They've shipped an intel/Linux binary, but I would be surprised if  
the current and next generation Neos have the horsepower to emulate  
the full skype library... I think they include their own codecs,  
which tends to eat up a lot of processor time.

The good news is that given Skype's ability to have multiple sessions  
open on the same account, it shouldn't be that difficult to create a  
client that transfers a Skype call from your handset to your desktop  
client without the person on the other end of the phone even being  

I have a similar problem in that I live in the sticks and coverage is  
a bit spotty, especially the last 30 seconds of my drive. I would  
love to "park" a call from my mobile and pick it up on my home phone.

The "holy grail" of home-based FMC would be a system that, like you  
describe, allows an incoming call to your home line to be forwarded  
to your mobile when you're away, and then transfer back to your home  
after you arrive. It's trivial to set things up to transfer from your  
land-line to a mobile line. You don't even need Asterisk to do that.  
But transferring back to the land line is a bit problematic.

In order to do this, you would need the complicity of your carrier or  
something like Asterisk listening in to the conversation. The former  
is unlikely to happen in this decade and the latter might require  
that you have two lines at your office; one to terminate the land- 
line call and the other to make the outgoing call to your mobile  
(with the PBX in the middle forwarding the sounds from one line to  
another and listening for signaling tones you produce to tell it to  
go into "call park mode.")

If you have an office in a business district, it's a lot easier to  
get a PBX interface where your phone system talks QSIG or DPNSS. In  
short, your equipment has a better mechanism for staying "in the  
loop" than with traditional analog residential signaling.

In the early days of ISDN and then later DSL and "Fiber to the Curb"  
there was a lot of talk about pushing intelligence to the leaves of  
the network specifically to support the types of things you're  
talking about. But such talk is heresy in the telco world, so we wind  
up with the status quo. The telcos seem to have built a pricing model  
based on differentiated "residential" and "business" services.  
Residential services tend to be cheaper, but offer fewer services.  
Business services cost a bit more (sometimes a lot more) but offer  
more flexibility and more services.

I've been making my own cell phones for over a year now, and I'm  
trying very hard to get the major carriers interested in service- 
differentiated MVNO's. Which is to say... a "Mobile Virtual Network  
Operator" that offers services different than the parent network. To  
date, it seems that most MVNO's are interested only in  
differentiating based on branding and marketing. I would think that a  
service that provided some of the services you're talking about would  
be great for small businesses. I'm thinking about a service that  
terminates a PSTN call (i.e. - a regular phone call) at our switch  
and then does VoIP to your desk (if you're at your desk) or forwards  
to your mobile, but stays "in the loop" with respect to signaling.  
When you want to transfer between land-line and mobile.

In other words, you would buy a SIP phone for your desk at home, and  
point it towards our proxy. We then provide a web interface that  
allows you to configure your service... voicemail, "follow-me" and  
the like... You would then get a normal mobile phone and configure  
the system to forward incoming calls to your mobile device and your  
desk phone. Then add the ability to use a SIP/RTP client over EVDO or  
EDGE if you want to try that. But the most important part of this  
system would likely be the ability to move calls between land-line,  
VoIP and mobile networks.

In a sense, this would be a lot like what I'm building at my day job  
at Divitas Networks. Our solution is targeted at businesses with (I  
think) something like 20 or more employees, so it's probably more  
than you want to pay. But... if someone else came in, bought one of  
our servers and then bundled our service with a mobile plan it would  
be a lot like what I'm taking about.

Anyway... you're not insane. I think the only reason what you're  
talking about can't be done already is that no one's done it yet.  
Whenever I bump into the Skype / eBay people online or at  
conferences, it's clear they're spooling up to compete head-to-head  
with the major telcos of the world, so it wouldn't be outside the  
realm of possibility for Skype to come up with a service very close  
to what you're after. Or... at least... if you could explain your  
requirements to the Skype guys, and their business guys did the  
analysis and found out it would be profitable for them, I can imagine  
them implementing such a thing in a couple of months. Assuming you  
could convince the telco guys to do such a thing, I'm sure they could  
do it within two or three decades.

-Matt H.

On Mar 28, 2007, at 12:59 PM, mathew davis wrote:

> I have an itch that I would like to explain to you and give an idea  
> of how to overcome that itch and see if that is possible or not,  
> and if so a good idea or not.  So first here is my itch.  I have a  
> VoIP phone at home which uses my WiFi connection to make calls  
> using skype.  I like that it helps lower my cell phone bills a lot  
> since I started a new business and it takes a lot of calls to make  
> it sucessful.  But I am not always at home sometimes I am just 5  
> minutes out from home and recieve a phone call I talk on the way  
> home and then to cut my minutes short I tell them I will call them  
> right back and then hang up switch to my VoIP phone.  That gets old  
> sometimes.  Granted it is not a very big itch but it is annoying.
> So I have come up with several solutions.  First, with the neo I  
> could get a plan that includes data with my minutes and I could use  
> skype or some other VoIP solution like astrisk.  Which in turn  
> would be great.  Oh also another question can you get a data only  
> plan?  Just curious I know some people may or may not have  
> mentioned it but the thread that it was mentioned in has over 80 e- 
> mails and couldn't find it right off.  But let's pretend that for  
> somereason you didn't want to add a data plan to your mobile device  
> because it was too expensive or what ever.  Would it be possible  
> for the neo to know when you step into range of a WiFi network that  
> you have acess to?  And after it notices the WiFi connection it  
> pops up a button on the screen that say's transfer to VoIP?  You  
> say hold on a sec and press the button.  The neo then puts the user  
> on hold and transfers the call to your VoIP line on your neo where  
> you pick it up, or the neo picks it up.  The voice line then hangs  
> up the call and puts the person back on the line with you.  Does  
> that make since?  Also when making a call and I am in range of a  
> WiFi network a check box or a seperate call with VoIP button  
> appears that allows you to place the same call over the VoIP?  Does  
> that make since?  Just wanting to get everyones opinions on this.
> This is a feature that I would like very much.  I have internet at  
> home which has a 15Mbps transfer rate with a 1000GB cap so I should  
> be free and clear with this.  I would love to have this feature.  I  
> would like to learn how to do this on the neo but would definatly  
> need more time to research it out.  Plus I would need more time to  
> work on it, maybe when I graduate school.  I would also need  
> someone to help me.  Any ways I am starting to ramble so please let  
> me know what you think about this?
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