Subject: Re: FWD: Re: what is the voice packet size?

From: Scott Bradner <[email-masked]>
Date: Sat, 12 Sep 1998 12:44:20 -0400 (EDT)

it is said:
Speech ceases to be interactive if the end to end delay is more than
250ms (Brady c1969).  If you are not offering a service in this
ballpark it isn't going to fly no matter how you price it. 

I seem to remember that satellite-based voice services did "fly" even when some
of them exceeded this magic number

in other words - absolutes are easy to understand but can be an over simplification

Scott
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From: "Reinaldo Penno Filho" <[email-masked]>
Date: Fri, 25 Jul 1997 06:17:14 -0300

-----Original Message-----
From: Scott Bradner <[email-masked]>
To: [email-masked] <[email-masked]>; [email-masked]
<[email-masked]>
Cc: [email-masked] <[email-masked]>
Date: Saturday, September 12, 1998 5:14 PM
Subject: Re: FWD: Re: what is the voice packet size?

>250ms (Brady c1969).  I

Paul Brady in his "bell labs time", great article.

>of them exceeded this magic number

I think that one of the reasons, (maybe the most important), that satellite
services did fly was because the lack of underwater cable infrastructure.

But  that's  my opinion.  We could have a good insight of this point if
someone had, for example,  some real data of telephones calls using
satellite before and after TAT-12/13 (10 Gb/s) was completed between USA and
Europe (1997).

I can tell from experience that voice calls from Brazil to the USA uses
satellite links because underwater cables between the two continents are
saturated.  Bandwidth in  Altantis I, the new cable from Brazil to Europe
and than to USA, is being disputed byte by byte between MCI, Telefonica  and
AT&T. Even thogh that's plenty of satellite channels available.

>in other words - absolutes are easy to understand but can be an over
simplification

Last time I checked delay tables, it was something like this

0-300ms  Acceptable for most applications

300-800ms Acceptable if implemented consciously.

What this means is that if you provide a +- 500 ms delay in a voice call
from USA to China its ok, because thats the best you can do with today's
infrastructure.

Now, if you provide the same delay from New York To Washington, its totally
out of the question. I mean, you can still sell it,  but your QoS is very
low

800+ms Unacceptable for most applications. Can be used in ecxeptional
situations.

Even here there are companies that sell voice calls with these kind of
delays delays. I know one, that sells voice calls from Brazil to USA using
Unidirectional Satellite links from USA to Brazil and Internet from Brazil
to the USA.

Best Regards,

 _________________________________
 Reinaldo Penno Filho
 Consultor Tecnico
 SAGA Sistemas e Computadores S.A.
 tel: 55-21-5508506
 e-mail : [email-masked]

 Universidade Federal do Rio de Janeiro
 Nucleo de Computacao Eletronica / Instituto de Matematica
 Grupo de Redes de Alta Velocidade
 e-mail : [email-masked]

 IEEE member
 e-mail : [email-masked]
 _________________________________

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From: "Reinaldo Penno Filho" <[email-masked]>
Date: Fri, 25 Jul 1997 08:07:44 -0300

-----Original Message-----
From: Scott Bradner <[email-masked]>
To: [email-masked] <[email-masked]>
Date: Sunday, September 13, 1998 12:21 AM
Subject: Re: FWD: Re: what is the voice packet size?

>Reinaldo mentions:
>even if the 500 msec call were to be offered at 10% of the price of the 300
msec call?
>
>I'm pushing back a bit here because I do not think that it is reasonable to
>pre guess what is "out of the question" (though I agree that 800 msec RTT
woulkd
>meet almost any test of "out of the question" )
>

I was not talking about what should or not should be done. I was merely
reproducing what's normally accepted in *carrier telephony*.  It was two
separate arguments. This part had to do with the satellite discussion.

My point is -  yes, everyone can sell ip telephony service. Even with a
larger delay. What I think that should be clear (maybe to the client) is the
tradeoff.

carrier delay (Optimum delay) vs offered delay and
carrier cost vs ip telephony cost.

This important to us, cause knowing how close we are from the optimum delay
and (consequently, in part) how much we should charge for the services, we
can tune our ip telephony services better.

>I'd rather aim at ensuring a quality that everyone agrees is better than
"OK" but
>not preclude serive offerings which may not meet that level of quality -
specifically
>I think that understanding what will sell is all that easy and we should
not
>assume that just because "we" would not like to buy the service that
everyone
>would agree.

Maybe we should define quality (not strictly) in the light of ip telephony.

>
>(I've said this before using a few more words.  If anyone has nothing
better to do they
>can let me know what they think of
http://golem.sobco.com/nww/1998/25-point.vs.curve.html)

Just read it.  See comments above.

Regards,

Reinaldo

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From: Krishna Kurapati <[email-masked]>
Date: Mon, 14 Sep 1998 07:51:29 -0500

Binshi,

     Though G.729 is 10 msec frame, some vendors are normalizing frames with G.723.1's frame time, that is
     30 msecs. 

     Also, it is configurable to place more than one frame in an RTP packet and Frame redundancy. Which makes
     packet length and interval between packets muliple of frame times.

     The practical side of it is, ethernet drivers, which are interrupt driven cannot handle several channels worth of
     G.729 and G.723.1 frames.

Krishna Kurapti
IPCell Technology, Inc
2011 North Collins Blvd
Suite 707 Richardson, TX 75080
(972) 671 2355

-----Original Message-----
From:	Binshi Cao [SMTP:[email-masked]]
Sent:	Friday, September 11, 1998 10:52 AM
To:	Jonathan Rosenberg
Cc:	[email-masked]
Subject:	Re: FWD: Re: what is the voice packet size?

Jonathan Rosenberg:

Thanks for your comments.

Jonathan Rosenberg wrote:
> 
> Binshi Cao wrote:
> >
> > In the Voice Over Internet (VOI) applications, G.711, G.723.1, G.729, etc, are
> > used. G.711, with 64 kbps bit rate, does not divide into frames itself; Some
> > venders use 10 mse and others use 20 msec as frame length and 25 msec may be too
> > long for G.711 used for VOI. G.723.1. with 5.3 or 6.3 kbps bit rate, uses 30
> > msec as frame length. G.729, with 8 kbps bit rate, uses 10 msec as frame length.
> >
> > Bit rate and frame length of a speech codec , plus transmission header, decide
> > the packet size.
> 
> Its not just the frame length. One can fit any number of frames in a
> packet. So, for G.723.1, the packetization delay can be 30, 60, 90ms,

Yes, you can have 30, 60, 90 ms delay (G.723.1) for the packetization.

But if the total dalay, including codec algorithm delay, processing daly,
transmission delay, is more than 60 - 100 ms, depending on the application,
people may perceive the delay and may not happy.  And furthermore, delay also
introduces the echo wich is annoying as well. Someone may say that echo
canceller may be applied in the system. But please think about what MIPs you may
provide in DSP for the echo canceller with delay of 60 ms more.

Thus, if the commercial products are designed, it is better that the packets
should be sent out according to frame length. 
 
> etc. Thus, the frame size defines the minimum packetization delay, and
> the granularity in general of the packetization delay.
> 
> -Jonathan R.
> 
> --
> Jonathan D. Rosenberg                       Lucent Technologies
> Member of Technical Staff                   101 Crawfords Corner Rd.
> High Speed Networks Research                Holmdel, NJ 07733
> FAX:   (732) 834-5379                       Rm. 4C-526
> EMAIL: [email-masked]
> URL: http://www.cs.columbia.edu/~jdrosen

Binshi Cao. << File: vcard.vcf >> 
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