tiny IAX/SIP switch?

[Guest]

Archived from groups: comp.dcom.voice-over-ip (More info?)

I'm hoping to give a demonstration of a mesh network between
farm vehicles soon. I'd like to use VoIP as the application.
I have lots of VoIP stuff already and I'm thinking of buying
some Cisco 7940 phones.

However...for most of the nodes I want to use Linksys WRT54G
wireless routers running OpenWRT (and OLSR for the mesh
routing). The problem is that I want the nodes to be able to
communicate with each other even when there is no path to the
wired network. (A situation would be two tractors working a
distant field with no trucks, etc. to relay back to the
barn.)

To do this I just realized that I'm going to want something
on the order of Asterisk running on each node, able to route
calls to any other node independently. The Linksys box has a
tiny amount of memory. I don't think Asterisk can begin to
fit in it.

So is there a very simple VoIP switch that can fit on a small
system like this? Do I need to roll my own with something
like libiax? Normally I'd want to use IAX but the only IAX
device I have is an IAXy (which didn't work well) so I'd
rather have something that can at least speak SIP to the
devices. I'm thinking IAX is probably better for being able
to move calls efficiently though.

Suggestions? Even reasons why it's not likely to work well
will be appreciated. I can still punt and use more powerful
systems than the WRT54G.

Thank you.

--kyler

 

[Guest]

Archived from groups: comp.dcom.voice-over-ip (More info?)

Kyler Laird <Kyler@news.Lairds.org> writes:
> I'm hoping to give a demonstration of a mesh network between
> farm vehicles soon. I'd like to use VoIP as the application.

This sounds like a very cool hack.

I don't believe you need a sip proxy at all to call between VOIP
phones. I can call between my Grandstreams by dialing the IP address
directly. It is a bit of a long "number" to dial, but for a quick
proof-of-concept demo it might be ok.

That would leave you with only having to do the code for the mesh
routing. I understand that isn't as easy as it first appears. The
MIT rooftop folks have some very uncharitable things to say about the
802.11b signaling protocol and how it is basically impossible to keep
their ad-hoc mesh from forming isolated islands.

www.pdos.lcs.mit.edu/papers/grid:bac-meng.pdf
www.pdos.lcs.mit.edu/papers/grid:losstr02/paper.pdf

-wolfgang
--
Wolfgang S. Rupprecht http://www.wsrcc.com/wolfgang/

 

[Guest]

Archived from groups: comp.dcom.voice-over-ip (More info?)

"Wolfgang S. Rupprecht" <wolfgang+gnus20040903T115628@dailyplanet.dontspam.wsrcc.com> writes:

>Kyler Laird <Kyler@news.Lairds.org> writes:
>> I'm hoping to give a demonstration of a mesh network between
>> farm vehicles soon. I'd like to use VoIP as the application.

>This sounds like a very cool hack.

We'll see. I'm just starting to work on it and it's only 11 days
away.
http://www.agry.purdue.edu/FieldDay/
I'm trying to bite off enough to be interesting but not so much
that I end up having to deal with lots of extra equipment, writing
software from scratch, bailing at the last minute, ...

>I don't believe you need a sip proxy at all to call between VOIP
>phones.

I had found a page on voip-info.org about being able to configure
Asterisk to set up a call between SIP devices and then get out
of the way, leaving them to speak directly to each other. I was
thinking that would be a start, but...

>I can call between my Grandstreams by dialing the IP address
>directly.

Ah ha! That would be *wonderful*. Any idea if that's supported
on Cisco 7940s?

>It is a bit of a long "number" to dial, but for a quick
>proof-of-concept demo it might be ok.

Oh, it's a perfect solution! I assume I can even use speed dials
to make it transparent.

>That would leave you with only having to do the code for the mesh
>routing. I understand that isn't as easy as it first appears.

It *is* easy. Well, for me, after playing with it for a long time
it's easy. I'm using OLSR. There's even an OpenWRT package for
it. I set it up last night with five devices (including my WRT in
my car in the driveway) and walked around the neighborhood with my
pen tablet. Geeky fun!

>The
>MIT rooftop folks have some very uncharitable things to say about the
>802.11b signaling protocol and how it is basically impossible to keep
>their ad-hoc mesh from forming isolated islands.

Oh, there are certainly non-trivial problems to overcome with mesh
networks but for a small example like this I think I'll be o.k. I
will probably try using CTS/RTS to deal with hidden nodes. It'll
be interesting to see how a SIP session survives.

Thank you for the info!

--kyler

 

[Guest]

Archived from groups: comp.dcom.voice-over-ip (More info?)

"Wolfgang S. Rupprecht" <wolfgang+gnus20040903T115628@dailyplanet.dontspam.wsrcc.com> writes:

>I don't believe you need a sip proxy at all to call between VOIP
>phones. I can call between my Grandstreams by dialing the IP address
>directly.

It looks like Sipura devices can do this too.
http://www.broadbandreports.com/forum/remark,9737256~mode=flat

I'll try to hook up a couple and give it a shot.

--kyler

 

[Guest]

Archived from groups: comp.dcom.voice-over-ip (More info?)

Kyler Laird <Kyler@news.Lairds.org> writes:
> "Wolfgang S. Rupprecht" <wolfgang+gnus20040903T115628@dailyplanet.dontspam.wsrcc.com> writes:
> We'll see. I'm just starting to work on it and it's only 11 days
> away.
> http://www.agry.purdue.edu/FieldDay/
> I'm trying to bite off enough to be interesting but not so much
> that I end up having to deal with lots of extra equipment, writing
> software from scratch, bailing at the last minute, ...

There is nothing like a bit of pressure for getting the creative
juices flowing. ;-)

> >I can call between my Grandstreams by dialing the IP address
> >directly.
>
> Ah ha! That would be *wonderful*. Any idea if that's supported
> on Cisco 7940s?

Sorry, I don't know much about the Ciscos. They were always way too
rich for my blood. (The ones I looked at were $350 w/o SIP firmware.)

> It *is* easy. Well, for me, after playing with it for a long time
> it's easy. I'm using OLSR. There's even an OpenWRT package for
> it. I set it up last night with five devices (including my WRT in
> my car in the driveway) and walked around the neighborhood with my
> pen tablet. Geeky fun!

If the connectivity between nodes is generally good, you should be ok.

What the MIT folks found is that the nodes in their northern Cambridge
mesh had a tendency to form different BSSID networks even though their
SSID's were set to the same value.

from: grid:bac-meng.pdf p.48

BSSID partitioning

When 802.11 interfaces are put into Ad Hoc mode, they go through
a somewhat complicated pro cedure to join what is known as a Basic
Service Set, or BSS [11]. A BSS is a kind of virtual network; even
if two different no des are op erating on the same channel, they
will not "see" each other's packets unless they are in the same
BSS. Basic Service Sets are identified by a 6-byte numb er known
as the Basic Service Set ID, or BSSID, which is transmitted in the
header of every 802.11 frame. When an 802.11b adapter enters Ad
Ho c mo de, it is configured with a Service Set ID (SSID), which
is a string that is intended to identify the network it wishes to
join. The adapter then scans through all of the 802.11b channels,
listening for b eacons sent by other no des. Beacons contain,
among other things, the SSID and BSSID b eing used by the sending
no de. If the adapter hears a beacon containing the SSID that
matches its own, then it joins this existing Basic Service Set by
setting its own BSSID to the one received in the beacon.

If the adapter does not receive any b eacons with a matching SSID
within a certain period of time, it decides that no Basic Service
Set currently exists with its SSID. In this case, it sets up
itself as a new Basic Service Set by selecting a random BSSID and
using that for all of its traffic. Any other no des using the same
SSID which start up in range of this no de will hear its beacons
and configure themselves to use its BSSID.

This creates a serious problem for an Ad Ho c network. Namely, if
two no des start up at different times and are not within radio
range of each other, they will start with different BSSIDs and b e
on different logical networks, despite b oth having the same
SSID. Because 802.11 adapters ignore all frames whose BSSID do es
not match their own, this creates a partition in the network and
prevents all of the nodes from being able to communicate
properly. Ideally, it would be possible to set the BSSID
directly to ensure that a given set of nodes would all be able
to communicate. Unfortunately, this is not possible using 802.11b
hardware.

> Thank you for the info!

My pleasure!

-wolfgang
--
Wolfgang S. Rupprecht http://www.wsrcc.com/wolfgang/