[kwlug disc.] Re: John's January 2007 VOIP presentation (outline)

[John Van Ostrand]

On Fri, 2007-01-26 at 18:03 -0500, Unsolicited wrote: 
> B. Switzer wrote, On 1/23/2007 8:34 PM:
> 
> I was very (very!) disappointed to be unable to attend the
> January meeting, due to the sudden onset of a head cold.
> 
> [BTW, whenever you intend to present this again, perhaps at a
> neighbouring LUG, please let the list know - I'd probably even be
> willing to travel to catch it after having missed this one.]
> 
> By any chance, could you expand on some of the points Charles has
> very kindly posted? [Other readers, if interested, please also
> encourage John here.]

I would be glad to. Perhaps this is a good topic for the new Cambridge
lug, or the newly forming London lug.


> Other questions:
> 
> Do you have a favourite first, K.I.S.S., site for a new person to
> go to to get up and running quickly and simply to start to get an
> initial handle on what the heck this stuff is all about? There
> appear to be many, many, sites out these days, and it can be
> daunting to first encounter the more deeply technical ones. Do
> you have a favourite?

I recommend www.trixbox.org as a good start for VoIP. It's not a howto
site, it's actually a "distribution" of asterisk that makes setup as
simple as possible. Until recently it was known as asterisk at home, but
changed names to appear more business friendly.

As for documentation I always use www.voip-info.org. It has good docs on
all devices, cards, etc and serves as a good reference.

> I see a number of hardware products out there which appear to be
> provider specific. e.g. Skype, Vonage. Does it actually matter?
> (When intending an Unlimitel account, say.)

These devices can be locked to a single provider, either by hard coded
values in firmware or because they use non-standard VoIP protocols.
These devices are often sold much cheaper than non-locked devices,
becase the VoIP provider intends to make it back in service revenue.
VoIP-info lists how to "unlock" some of these devices for Asterisk use.
Examine your ethics and see if you want to do this.

> In an earlier list thread, I posted:
> 
> Unsolicited at gto.net wrote, On 12/14/2006 7:21 AM:
> > Speaking of that ...
> >
> > John ... any chance you can post a couple of things to the
> list before
> > you actually present in January?
> >
> > 1. I saw a reference in an earlier message to a 'LinkSys
> SPA3000' but
> > can't find it. (I did get a sense that LinkSys had just bought
> somebody
> > who had it but ...). Can you post a link? At the time, I was
> just trying
> > to figure out what sort of beasties were involved in this 'topic'.

LinkSys purchased Sipura. You can still access the Sipura site at
http://www.sipura.com. LinkSys has the PAP2 and the SPA2002 devices and
my distributor shows lots of other spa* devices from Linksys.
http://www.voipdepot.ca is where I purchased before going directly to a
distributor.

> > 2. From what I read, there are advocates of putting the
> beastie in front
> > of your router, behind it, and some to the side - depending on
> who
> > you're reading at the time. Can you post to the list your
> favourite
> > location, a la your January presentation for a $2.50/month
> phone line?

My favourite location is behind a firewall. If it's an asterisk box I
may make it a firewall too.

The main reason for differing opinions on where to logically place your
VoIP device is due to two factors:

1. Audio quality is usually degraded unless the router/firewall gives
preference to VoIP traffic. For example: if you are uploading a huge
file to a server, those data packets will be large and will delay the
VoIP traffic. If the VoIP traffic is delayed too much, the receiving end
will discard the late packets. If the receiving end waited for every
packet so that it could play them in sequence, the conversational delay
would increase indefinitely as the call progressed. The solution is to
discard packets that are too late. When this happens the audio sounds
choppy, like a bad digital cell phone call. 

2. SIP configurations often have trouble with network address
translation (NAT). This is because the SIP protocol encodes the IP
address (your 192.168.x.x) into the data stream. Many firewalls don't
look for this and won't change it. The result is that the remote server
gets confused, seeing a routable address in the packet header and a
non-routable address in the request data. Using a VoIP enabled
firewall/router will alleviate this. This can also be alleviated in most
topologies by proper configuration.

So how does one eliminate these issues?

You could use an all-in-one device that includes a router/firewall.
These are often configured to give preference to VoIP traffic to
alleviate factor 1. The VoIP device would also have the routable IP
address alleviating factor 2 as an issue. This is preferred by VoIP
telcos because then they don't have to waste time supporting your
firewall. The problem with this approach is if you need to use a second
VoIP device. Where do you put it?

You can also find a router that supports traffic shaping (sending VoIP
packets first.) Linux will do this, a WRT54GL with OpenWRT will do this,
an IPCop box with a suitable plugin will also do that.
I've been 
I have never used and all-in-one VoIP/Router/Firewall device as a
firewall. This is mostly because I prefer to use Linux.

What I can tell you is that if you use traffic shaping (QoS) then the
audio you are sending will sound better.

I can also say that if you are pushing a lot of traffic on your Internet
connections (e.g. downloading, p2p sharing) then you will have audio
problems. You will have to do things to alleviate that and that may
include QoS or a separate Internet connection for you VoIP.

> >     - given the rate of technological change, e.g. 300Mbps
> Wi-Fi coming,
> > etc., I have the impression that one may be smart, today, to keep
> > certain functionality in different boxes for ease of future
> change. e.g.
> > Your router box, wi-fi box, and FXS/FXO box (keeping in mind QoS
> > capabilities throughout). Does that impression resonate?

If you are comfortable (and successful) supporting your home network as
several devices then go for it. It provides the most flexibility and it
can work for you. Some people will not want to work with all those
different devices and may opt for simplicity over leading edge.

> I don't remember seeing a response. Perhaps I missed it?

I may have missed it.

-- 
John Van Ostrand                       Net Direct Inc.
CTO, co-CEO                   564 Weber St. N. Unit 12
                                  Waterloo, ON N2L 5C6
john at netdirect.ca                     ph: 518-883-1172 x5102
Linux Solutions / IBM Hardware        fx: 519-883-8533
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