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Hi everybody,

For our next project, we need to develop & engineer a VOIP gateway which
must support 8 radio channels. The codec is G.711 . The requirement for the
latency of voice on the gateway is 1/4 seconds. My gut feeling says that we
can accomplish this with by using a 8 channel professional sound card
(~$200) and PJSIP library without using a DSP, with the help of a Intel i7
processor and Linux OS. But everyone says it's impossible without using a
DSP because of the CPU overhead of RTP packets and G.711 codec handling.

Can I ask for your opinion? Do we really need a DSP (PCI) card? If yes, can
you recommend a reliable & affordable DSP for our basic ROIP? 

Thank you.

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alpb wrote:

> For our next project, we need to develop & engineer a VOIP gateway which
> must support 8 radio channels. The codec is G.711 . The requirement for the
> latency of voice on the gateway is 1/4 seconds. My gut feeling says that we
> can accomplish this with by using a 8 channel professional sound card
> (~$200) and PJSIP library without using a DSP, with the help of a Intel i7
> processor and Linux OS. But everyone says it's impossible without using a
> DSP because of the CPU overhead of RTP packets and G.711 codec handling.

A 100MHz PC can handle that easily. The "G.711 codec" is just one table 
lookup operation. Do everything by hand, don't need any libraries and 
linuxes.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com

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On Jun 7, 9:39=A0am, "alpb" <alpbozkurt78@n_o_s_p_a_m.gmail.com> wrote:
> Hi everybody,
>
> For our next project, we need to develop & engineer a VOIP gateway which
> must support 8 radio channels. The codec is G.711 . The requirement for t=
he
> latency of voice on the gateway is 1/4 seconds. My gut feeling says that =
we
> can accomplish this with by using a 8 channel professional sound card
> (~$200) and PJSIP library without using a DSP, with the help of a Intel i=
7
> processor and Linux OS. But everyone says it's impossible without using a
> DSP because of the CPU overhead of RTP packets and G.711 codec handling.
>
> Can I ask for your opinion? Do we really need a DSP (PCI) card? If yes, c=
an
> you recommend a reliable & affordable DSP for our basic ROIP?
>
> Thank you.

I'm not sure who "everyone" is, but they might be referring to the
fact that most PC operating systems are not designed for hard real-
time operation, which your hard requirement on latency would suggest.
Contemporary Linux kernels do have some real-time extensions available
to mitigate this, but I don't have much experience with that. While
I'm not familiar with G.711, I would be very surprised if a modern x86
processor like an Intel i7 would have any issue supporting the
processing load of 8 voice-grade channels. Your main issue is just
ensuring that your processing task gets enough precedence to meet your
latency requirements without being elbowed out of the way by other
processes on the system.

Jason

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On 06/07/2011 07:36 AM, Jason wrote:
> On Jun 7, 9:39 am, "alpb"<alpbozkurt78@n_o_s_p_a_m.gmail.com>  wrote:
>> Hi everybody,
>>
>> For our next project, we need to develop&  engineer a VOIP gateway which
>> must support 8 radio channels. The codec is G.711 . The requirement for the
>> latency of voice on the gateway is 1/4 seconds. My gut feeling says that we
>> can accomplish this with by using a 8 channel professional sound card
>> (~$200) and PJSIP library without using a DSP, with the help of a Intel i7
>> processor and Linux OS. But everyone says it's impossible without using a
>> DSP because of the CPU overhead of RTP packets and G.711 codec handling.
>>
>> Can I ask for your opinion? Do we really need a DSP (PCI) card? If yes, can
>> you recommend a reliable&  affordable DSP for our basic ROIP?
>>
>> Thank you.
>
> I'm not sure who "everyone" is, but they might be referring to the
> fact that most PC operating systems are not designed for hard real-
> time operation, which your hard requirement on latency would suggest.
> Contemporary Linux kernels do have some real-time extensions available
> to mitigate this, but I don't have much experience with that. While
> I'm not familiar with G.711, I would be very surprised if a modern x86
> processor like an Intel i7 would have any issue supporting the
> processing load of 8 voice-grade channels. Your main issue is just
> ensuring that your processing task gets enough precedence to meet your
> latency requirements without being elbowed out of the way by other
> processes on the system.

Whether your app will get the attention it deserves depends, in turn, on 
what else is going on with your machine.  If you're going to have 
dedicated hardware that does nothing but implement your VOIP gateway, 
then you'll have control over all the apps, you'll be able to fine-tune 
the Linux installation, and _my_ gut feel is that you have a good chance 
of success.

If, on the other hand, you're trying to do this on a machine to which 
everyone and his brother has access, then you've got a tough row to hoe. 
  Keep in mind, too, that the more you depend on the processor to keep 
the data moving, the less flexibility you have to add apps -- if your 
marketing or product management team sees that box as an infinite sink 
for the latest whiz-bang 3rd-party apps, then you're doomed.  If, on the 
other hand, you retain total control and feature creep does not become 
feature sprint, then you may be OK.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html

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On Tue, 07 Jun 2011 08:39:44 -0500, alpb wrote:
> For our next project, we need to develop & engineer a VOIP gateway which
> must support 8 radio channels. The codec is G.711 . The requirement for
> the latency of voice on the gateway is 1/4 seconds. My gut feeling says
> that we can accomplish this with by using a 8 channel professional sound
> card (~$200) and PJSIP library without using a DSP, with the help of a
> Intel i7 processor and Linux OS. But everyone says it's impossible
> without using a DSP because of the CPU overhead of RTP packets and G.711
> codec handling.

Out of interest, which professional 8 channel sound cards support Linux?  
Do they have open or closed-source drivers?  Back in the PCI days there 
used to be support for RME Hammerfall, I think, but I don't know that 
that continued into the realm of PCIE or USB/Firewire versions.  Been a 
while since I looked, though.

I ask because I think that would be a nice DSP development environment, 
but most of the 8-chan sound cards that I've seen lately only claim 
Windows (not good for RT) or Mac (excellent RT but single-source 
hardware).

Cheers,

-- 
Andrew

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On Jun 7, 3:39=A0pm, "alpb" <alpbozkurt78@n_o_s_p_a_m.gmail.com> wrote:
> Hi everybody,
>
> For our next project, we need to develop & engineer a VOIP gateway which
> must support 8 radio channels. The codec is G.711 . The requirement for t=
he
> latency of voice on the gateway is 1/4 seconds. My gut feeling says that =
we
> can accomplish this with by using a 8 channel professional sound card
> (~$200) and PJSIP library without using a DSP, with the help of a Intel i=
7
> processor and Linux OS. But everyone says it's impossible without using a
> DSP because of the CPU overhead of RTP packets and G.711 codec handling.
>
> Can I ask for your opinion? Do we really need a DSP (PCI) card?

Yes, you do need the DSP.

While it might be *technically* possible to pull this off with
a linux box, provided you get it all to yourself and are granted
total contorl of what it does and how, you will never succeed.
Because you will never get that linux box all to yourself, nor
will you be granted total control of what it does and how.

Once that box is placed inside whatever system you are working on,
somebody - not you - will some time see it, and realize that it
is a huge resource. And start adding bells and whistles to it.
Once *that* happens, your application is screwed.

So get on with the DSP. That way you use only the resources
necessary to get the job done, at the same time you protect
those resources from future interference.

Rune

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>On Jun 7, 3:39=A0pm, "alpb" <alpbozkurt78@n_o_s_p_a_m.gmail.com> wrote:
>> Hi everybody,
>>
>> For our next project, we need to develop & engineer a VOIP gateway
which
>> must support 8 radio channels. The codec is G.711 . The requirement for
t=
>he
>> latency of voice on the gateway is 1/4 seconds. My gut feeling says that
=
>we
>> can accomplish this with by using a 8 channel professional sound card
>> (~$200) and PJSIP library without using a DSP, with the help of a Intel
i=
>7
>> processor and Linux OS. But everyone says it's impossible without using
a
>> DSP because of the CPU overhead of RTP packets and G.711 codec
handling.
>>
>> Can I ask for your opinion? Do we really need a DSP (PCI) card?
>
>Yes, you do need the DSP.
>
>While it might be *technically* possible to pull this off with
>a linux box, provided you get it all to yourself and are granted
>total contorl of what it does and how, you will never succeed.
>Because you will never get that linux box all to yourself, nor
>will you be granted total control of what it does and how.
>
>Once that box is placed inside whatever system you are working on,
>somebody - not you - will some time see it, and realize that it
>is a huge resource. And start adding bells and whistles to it.
>Once *that* happens, your application is screwed.
>
>So get on with the DSP. That way you use only the resources
>necessary to get the job done, at the same time you protect
>those resources from future interference.

That is not an argument for using a DSP. Its a pretty valid argument for
using a dedicated processor. For the poster's workload many MCUs will do a
much better job that a DSP. G.711 is trivial. His main work is RTP and
TCP/IP handling. Its much better *not* to do those on a DSP.

Steve

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On Jun 8, 8:10=A0am, "steveu" <steveu@n_o_s_p_a_m.coppice.org> wrote:
> >On Jun 7, 3:39=3DA0pm, "alpb" <alpbozkurt78@n_o_s_p_a_m.gmail.com> wrote=
:
> >> Hi everybody,
>
> >> For our next project, we need to develop & engineer a VOIP gateway
> which
> >> must support 8 radio channels. The codec is G.711 . The requirement fo=
r
> t=3D
> >he
> >> latency of voice on the gateway is 1/4 seconds. My gut feeling says th=
at
> =3D
> >we
> >> can accomplish this with by using a 8 channel professional sound card
> >> (~$200) and PJSIP library without using a DSP, with the help of a Inte=
l
> i=3D
> >7
> >> processor and Linux OS. But everyone says it's impossible without usin=
g
> a
> >> DSP because of the CPU overhead of RTP packets and G.711 codec
> handling.
>
> >> Can I ask for your opinion? Do we really need a DSP (PCI) card?
>
> >Yes, you do need the DSP.
>
> >While it might be *technically* possible to pull this off with
> >a linux box, provided you get it all to yourself and are granted
> >total contorl of what it does and how, you will never succeed.
> >Because you will never get that linux box all to yourself, nor
> >will you be granted total control of what it does and how.
>
> >Once that box is placed inside whatever system you are working on,
> >somebody - not you - will some time see it, and realize that it
> >is a huge resource. And start adding bells and whistles to it.
> >Once *that* happens, your application is screwed.
>
> >So get on with the DSP. That way you use only the resources
> >necessary to get the job done, at the same time you protect
> >those resources from future interference.
>
> That is not an argument for using a DSP. Its a pretty valid argument for
> using a dedicated processor.

Dedicated *processor*, not dedicated *PC*.

> For the poster's workload many MCUs will do a
> much better job that a DSP. G.711 is trivial. His main work is RTP and
> TCP/IP handling. Its much better *not* to do those on a DSP.

DSP with a network or comm interface integrated? The OP
can't be the first person in history to face kind of task?

Rune

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>On Jun 8, 8:10=A0am, "steveu" <steveu@n_o_s_p_a_m.coppice.org> wrote:
>> >On Jun 7, 3:39=3DA0pm, "alpb" <alpbozkurt78@n_o_s_p_a_m.gmail.com>
wrote=
>:
>> >> Hi everybody,
>>
>> >> For our next project, we need to develop & engineer a VOIP gateway
>> which
>> >> must support 8 radio channels. The codec is G.711 . The requirement
fo=
>r
>> t=3D
>> >he
>> >> latency of voice on the gateway is 1/4 seconds. My gut feeling says
th=
>at
>> =3D
>> >we
>> >> can accomplish this with by using a 8 channel professional sound
card
>> >> (~$200) and PJSIP library without using a DSP, with the help of a
Inte=
>l
>> i=3D
>> >7
>> >> processor and Linux OS. But everyone says it's impossible without
usin=
>g
>> a
>> >> DSP because of the CPU overhead of RTP packets and G.711 codec
>> handling.
>>
>> >> Can I ask for your opinion? Do we really need a DSP (PCI) card?
>>
>> >Yes, you do need the DSP.
>>
>> >While it might be *technically* possible to pull this off with
>> >a linux box, provided you get it all to yourself and are granted
>> >total contorl of what it does and how, you will never succeed.
>> >Because you will never get that linux box all to yourself, nor
>> >will you be granted total control of what it does and how.
>>
>> >Once that box is placed inside whatever system you are working on,
>> >somebody - not you - will some time see it, and realize that it
>> >is a huge resource. And start adding bells and whistles to it.
>> >Once *that* happens, your application is screwed.
>>
>> >So get on with the DSP. That way you use only the resources
>> >necessary to get the job done, at the same time you protect
>> >those resources from future interference.
>>
>> That is not an argument for using a DSP. Its a pretty valid argument
for
>> using a dedicated processor.
>
>Dedicated *processor*, not dedicated *PC*.
>
>> For the poster's workload many MCUs will do a
>> much better job that a DSP. G.711 is trivial. His main work is RTP and
>> TCP/IP handling. Its much better *not* to do those on a DSP.
>
>DSP with a network or comm interface integrated? The OP
>can't be the first person in history to face kind of task?
>
>Rune

They exist, but he isn't doing any DSP at all. Why make life hard? Use the
right tool for the job, which is not a DSP.

Steve

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On Jun 8, 11:28=A0am, "Steve Underwood"
<coppice@n_o_s_p_a_m.coppice.org> wrote:
> >On Jun 8, 8:10=3DA0am, "steveu" <steveu@n_o_s_p_a_m.coppice.org> wrote:
> >> >On Jun 7, 3:39=3D3DA0pm, "alpb" <alpbozkurt78@n_o_s_p_a_m.gmail.com>
> wrote=3D
> >:
> >> >> Hi everybody,
>
> >> >> For our next project, we need to develop & engineer a VOIP gateway
> >> which
> >> >> must support 8 radio channels. The codec is G.711 . The requirement
> fo=3D
> >r
> >> t=3D3D
> >> >he
> >> >> latency of voice on the gateway is 1/4 seconds. My gut feeling says
> th=3D
> >at
> >> =3D3D
> >> >we
> >> >> can accomplish this with by using a 8 channel professional sound
> card
> >> >> (~$200) and PJSIP library without using a DSP, with the help of a
> Inte=3D
> >l
> >> i=3D3D
> >> >7
> >> >> processor and Linux OS. But everyone says it's impossible without
> usin=3D
> >g
> >> a
> >> >> DSP because of the CPU overhead of RTP packets and G.711 codec
> >> handling.
>
> >> >> Can I ask for your opinion? Do we really need a DSP (PCI) card?
>
> >> >Yes, you do need the DSP.
>
> >> >While it might be *technically* possible to pull this off with
> >> >a linux box, provided you get it all to yourself and are granted
> >> >total contorl of what it does and how, you will never succeed.
> >> >Because you will never get that linux box all to yourself, nor
> >> >will you be granted total control of what it does and how.
>
> >> >Once that box is placed inside whatever system you are working on,
> >> >somebody - not you - will some time see it, and realize that it
> >> >is a huge resource. And start adding bells and whistles to it.
> >> >Once *that* happens, your application is screwed.
>
> >> >So get on with the DSP. That way you use only the resources
> >> >necessary to get the job done, at the same time you protect
> >> >those resources from future interference.
>
> >> That is not an argument for using a DSP. Its a pretty valid argument
> for
> >> using a dedicated processor.
>
> >Dedicated *processor*, not dedicated *PC*.
>
> >> For the poster's workload many MCUs will do a
> >> much better job that a DSP. G.711 is trivial. His main work is RTP and
> >> TCP/IP handling. Its much better *not* to do those on a DSP.
>
> >DSP with a network or comm interface integrated? The OP
> >can't be the first person in history to face kind of task?
>
> >Rune
>
> They exist, but he isn't doing any DSP at all. Why make life hard? Use th=
e
> right tool for the job, which is not a DSP.

We could probably quarrel over semantics till the cows come home.
In a real-time setting I'd still go for the smallest possible
device that could get the job done. Simply to discourage others
from elbowing in on tempting computational resources.

Rune

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