Soft VoIP

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Hi,

Is it OK to implement VoIP protocol merely by an 8 bit MCU and an
ethernet chip? The MCU speed is less than 10MHz. Or I need stronger MCU
such as ARM?

Thanks!


Re: Soft VoIP
What sort of protocol do you intend to implement? The VoIP
implementations I have seen in desktop phones used (8051) cores with
custom DSP add-ons.


Re: Soft VoIP
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Yep.  IIRC, the Cisco phones use a 386sx (or used to) - even back before
they had the fancy display.  Probably using something even beefier now.

It'd depend a lot on the CODEC.  G.711 might be possible with a straight
MCU + A/D, since it doesn't involve compression.  At 8bits x
8Ksamples/sec, it seems possible on the surface.  It'd be an interesting
attempt.

Re: Soft VoIP
But a 386sx is a 32 bits MCU!


Re: Soft VoIP
Well, it's better classified as a 16-bit CPU, since (a) it's not an
MCU, (b) it's slower, clock-for-clock than its pure-16bit parent the
80286, and (c) it has 16-bit external buses.

But the point in this specific topic is that a bare 8-bit core is
probably not sufficient for a credible VoIP implementation. You need
either a meatier core or external DSP assistance.


Re: Soft VoIP
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Ditto what Lewin said.

My point was that even back before the displays and on-phone apps, they
were using a beefy CPU.  But, they also supported G.729 compressed
CODECs then, which I expect is no lightweight job.

Look under the hood at the H.323 protocols, and evaluate:
* What kind of tasks need to be done every X milliseconds
* Roughly, how many cycles you'd need to do each one
* How much latitude is there in the timing (e.g., jitter)
* How many cycles will it take to encode and decode the audio streams?

For example, 8000x/second you need to read and encode a sample, and
presumably decode and playback another.  50-100x/second you need to send
and receive UDP Ethernet packets.  Good news is that UDP transport has
little overhead once you've built the data payload.

Things would get more complex as you add more features like silence
suppression, jitter buffering, error recovery, call initiation, etc.  I
think the real question is the effort involved in encoding the
8Ksamples/sec into G.711 packets.

It's possible that a basic G.711 VoIP phone could be within the grasp of
an 8-bitter running 8-16MHz.  But by limiting it to G.711 CODEC, it
would only be useful in a LAN environment, not across the Internet
(G.711 is a ~64Kbps stream).

Cheers,
Richard

Re: Soft VoIP


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It would still be great to build it in sub $10-20 range and use with
Asterisk backend. Hmm sounds like a profitable project. Any takers ?

Pozdrawiam.
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Re: Soft VoIP
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8 Bit CPU maybe yes, but not with the usual 64k RAM. You do need
an IP stack (propably even with TCP) and one of signalling protocols
(SIP, H.323). I can assure you, this requires a significant amount of
code and data memory.
Even if only doing G.711 you might need to do DTMF and/or tone
generation for your phone (not even thinking of stuff like echo
cancellation, comfort noise generation, local echo, ...)

Why not pick one of the existing VoIP solutions. I.e. TI has some stuff
well suited for IP phones (Telogy). It's a bit overkill for your application
but it comes with a MIPS R4000, TI DSP, Operating System and all
required software. Just attach a speaker/headphone/keyboard and
you're done. Pricing depends on volume, maybe 20..30US$.

Yours
- Rene (developing VoIP gateways/routers for the last 4 years)

PS. I am not with TI.




Re: Soft VoIP


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even less


4KB


+2KB, but its luxury we dont need

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asterisk will take care of that

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thats why asterisk box would do that work

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all that done on asterisk box :)

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 pice ? >$60

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with >10k volumes i presume :)

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And it shows, you are thinking one big fat box doing all the work.
I'm thinking bunch of small rj45/rj11 dongles + one asterisk box
doing backend. Those dongles would be /dev/dsp extenders. Even G.711
is not needed that badly.
You see fancy display + Wifi + VPN while I see "lets scrap that rj11
circuit and build it inside the phone enclosure".

Pozdrawiam.
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Re: Soft VoIP
----- Original Message -----
Newsgroups: comp.arch.embedded
Sent: Wednesday, December 22, 2004 10:40 AM
Subject: Re: Soft VoIP


[Cut]

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You did not specify technical details before. If you want Asteriks to do
all signalling you could hook up an ordinary phone to the Asteriks
PC (buy a compatible FXS card for the PC).

But I guess this is not what you had in mind. You're are more thinking
of a "dump" phone, that does minimal signalling and data processing,
connected to an Ethernet. I think something like this can be done
with an 8 bit micro and some clever programming (similar to an
ISDN telephone).

If you're done let us know how much resources you used in the end.

- Rene



Re: Soft VoIP

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exactly, no need for 32bit mips in every room of the building

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Those cards are ~$50-100. Plus ethernet cables are everywhere, no
need to drill the walls again.

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exactly. Its beyond me that nobody has think of it before.

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MCU $2-4
DAC $1-3
ethernet $2-3 (RTL8019)
enclosure,sockets,pcb,trafo,powersupply - $10 ?

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It sounds more and more interesting every minute i think about it.
I'l try to convince few friend into this.

Pozdrawiam.
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Re: Soft VoIP
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FYI I've done this for a consulting gig, ATMEGA64, SILabs SLIC and a
realtek eth controller.

2:1,3:1 and 4:1 compression and decompression on the fly.

mike



Re: Soft VoIP
Grandstream uses a Texas Instruments Fix point DSP
and snom formerly a PowerPC but the snom 190 changed to Infineons Tricore

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