[SIPForum-discussion] SIP Account

[Arnoud van Wijk]

Hi all,

The problems with fax over IP what happens here are exactly the same 
issues that happens with text telephony over IP.
Many manufacturers happily explain to me that Boudot, V.21 and other 
text telephone protocols will work without a problem using VoIP.
All stating that they did test and that most users will have VoIP pipes 
that were big enough that they were fairly confident in having a very 
minimal, if any, amount of lost packets.

You only need 1 trunk or 1 gateway that is only dealing with VoIP and is 
configured to do so and poof there goes the fax and the text telephone.

T.38 for fax remains the best way as well RFC4103 for text telephony.

That is and remains the real-world situation.

cheers

Arnoud

On 4/30/10 7:50 PM, Maciej Wasiel wrote:
>
> As someone who implements t.38 and fax-passthough (RTP) stacks for a 
> living and tests them against MANY media gateways, I can assure you 
> that RTP (passthrough) fax solutions are VERY inferior to t.38. 
> Packets loss is only one impairment and in many cases it may not be 
> the most significant. The problem stems from the fact that many media 
> gateways treat RTP fax traffic like voice, which is a big no-no for 
> fax. Silence suppression, jitter buffer underruns/overruns, and clock 
> skew can be very damaging to modulated data whereas with voice these 
> impairments can often go unnoticed. When you get into V.34 (SG3) fax, 
> fax passthrough calls are even more likely to experience problems due 
> to the non-packet loss impairments I mentioned above.
>
> ------------------------------------------------------------------------
>
> *From:* discussion-bounces at sipforum.org 
> [mailto:discussion-bounces at sipforum.org] *On Behalf Of *Umang
> *Sent:* Thursday, April 29, 2010 3:17 PM
> *To:* Jason Chow
> *Cc:* discussion at sipforum.org
> *Subject:* Re: [SIPForum-discussion] SIP Account
>
> I used to work for a very large telecommunications company (ISP).  
> After months of research, testing, and deliberation, it was decided 
> that Fax would be implemented in in our residential and business 
> networks using just the regular RTP, without any T.38.  I believe T.38 
> can be used over UDP or TCP, but for our purposes, the extra 
> processing did not matter, our VoIP pipes were big enough that we were 
> fairly confident in having a very minimal, if any, amount of lost packets.
>
> Also, the user agent we were developing had some short comings with 
> responding to T.38 packets, but you might be in a different 
> situation.  Hope this was of some help.
>
> Umang Patel | Communications Research Engineer | Massachusetts 
> Institute of Technology
>
> On Thu, Apr 29, 2010 at 3:34 AM, Jason Chow <myfaxcn at gmail.com 
> <mailto:myfaxcn at gmail.com>> wrote:
>
> Dear Sir, I'm looking for the Service Providers support t38 fax, Can 
> help me to recommend? Thanks!
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> -- 
>
> Umang
>
>
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-- 
Director
Foundation Real-Time Text Taskforce
http://www.realtimetext.org/

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