t.38 on a HandyTone-486 to 2talk

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richms

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Topic # 27103 14-Oct-2008 16:26

How reliable is this?

It would be at a friends place who is with orcon wholesaled internet as a replacement for faxability which keeps waking them up. The handytone is only $50 on trademe, it lists T38, which I understand 2talk support.

Also how resiliant is t38 to a no qos situation, I understand the bandwidth needed will be way less then a g711 call, but is it less sensitive to jitter? Is there any resiliancy to lost packets either thru the fax machines ECM or native to the T38 transport?

Richard rich.ms

cisconz

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Reply # 171127 14-Oct-2008 19:12

handytone =/= reliable

Hmmmm

hads

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Reply # 171135 14-Oct-2008 20:05

We don't recommend the Grandstream Handytone devices. In some circumstances they work fine but I wouldn't count on their T.38 implementation.

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richms

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Reply # 171158 14-Oct-2008 20:56

Ok thanks, looks like fax to email it is then, unless their is a comparably priced reliable t38 ata?

Richard rich.ms

Glazza

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Reply # 171159 14-Oct-2008 21:06

I use a SPA2102 with 2talk....

T38 is great....

hads

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Reply # 171160 14-Oct-2008 21:08

Yes, the Linksys ATAs aren't too bad, probably the best choice for the price range.

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nate

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Reply # 171277 15-Oct-2008 13:42

cisconz: handytone =/= reliable

Not too sure what programming language cisconz is quoting above (it should be handytone != reliable or handytone <> reliable)

+1 for avoiding anything in the Grandstream range.

To answer your query, T38 has got better resiliancy to jitter than faxing overs say G711. From your post it sounds like the faxes are coming in during sleeping hours, and as long as your friend hasn't got downloads going, you should be fine.

Otherwise, a rock solid Draytek router will sort out that QoS issue.

richms

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Reply # 171284 15-Oct-2008 14:08

Ok, well they are probably just going to move to the 2talk anyway with fax to email for now, and worry about an ata later on.

Thanks all for steering me off the handytone path...

Richard rich.ms

cisconz

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Reply # 171293 15-Oct-2008 15:09

nate:
cisconz: handytone =/= reliable

Not too sure what programming language cisconz is quoting above (it should be handytone != reliable or handytone <> reliable)

I couldn't find a does not equal symbol like they use in math’s books.
I am not a programmer like you.

/me bows down to Nate’s superiority

Hmmmm

coffeebaron

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Reply # 171301 15-Oct-2008 15:49

nate: To answer your query, T38 has got better resiliancy to jitter than faxing overs say G711. From your post it sounds like the faxes are coming in during sleeping hours, and as long as your friend hasn't got downloads going, you should be fine.

How reliable is T.38 these days? The issue's I've had is often T.38 does not kick in, therefore reverts to G711. That's all fine on a good DSL connection, but when DSL is not running well, it all goes to custard.

Why does T.38 not always kick in?

Any difference in reliability between 2talk & VFX for faxing over T.38? (From the context of a home business user who won't be using commercial grade fax machine or T.38 ATA).

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cisconz

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Reply # 171364 15-Oct-2008 21:35

coffeebaron: How reliable is T.38 these days? The issue's I've had is often T.38 does not kick in, therefore reverts to G711. That's all fine on a good DSL connection, but when DSL is not running well, it all goes to custard.
Why does T.38 not always kick in?
Any difference in reliability between 2talk & VFX for faxing over T.38? (From the context of a home business user who won't be using commercial grade fax machine or T.38 ATA).
Cheers

T.38 sends the fax data 4 times, that is why it is so much more reliable.
T.38 only kicks in if both ends support it.
2talk is interoprable with vfx for faxing.
there is no reliablility difference except that using 2talk's faxmail doesnt rely on your dsl connection.

Hmmmm

Glazza

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Reply # 171376 15-Oct-2008 22:32

by both ends, I assume you mean your VoIP provider and the ATA.... The calling parties fax machine, or your fax machine do not need to support T.38....

The call to the ATA device is dialled as normal, but when the fax machine starts to transmit its analogue fax signal, the ATA which it's connected decodes the analogue audio signal back into digital form locally, transmits it to the remote VoIP Switch (2talk, VFX, whoever), which then creates a new analogue signal for the remote fax machine. In this way, the analogue signal is not transmitted across the Internet and therefore you remove the potential for the VoIP encoded analogue signal suffering from loss or delay.

T.38 includes two methods of error correction to recover from minor packet loss. The data stream is transmitted with redundant (duplicated) data and checksums (CRCs). This way, if the receiving gateway detects that a packet has been lost or corrupted, it can extract it from the redundant data.

T.38 also uses FEC (forward error correction) appended to the end of each T.38 packet.

There are also different standards for T.38, than generally need to be configured in ATA - otherwise it may try to use a standard that is not supported by the VoIP providers switch - one example is V.34 FAX - I don't know about VFX, but 2talk dont support this.

With testing, I can be receiving a fax, unplug the ATA from the network for a couple of seconds, plug it back, and I will still receive the fax - it did take a bit to get working, but no it is working, it is rock solid - using 2talk. Previously I tried VFX, but I assume at this point in time they were using G.711, as I never really had any luck...

Cheers

coffeebaron

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Reply # 171590 16-Oct-2008 16:27

cisconz:
T.38 only kicks in if both ends support it.

Can you clarify this a bit more Dave? What is "both ends" i.e.
- Is T.38 only applicable if both end points are VoIP? e.g. VFX-VFX, or VFX-2talk etc
- Is T.38 applicable with PSTN <-> VoIP. e.g. a fax call comes in from PSTN, enters say WxC, terminates on a VFX line; does the WxC PSTN gateway not kick in and convert to T.38?
- Or is it the fax machine at either end that is the issues here?

I'm just trying to work out why T.38 sometimes works and some times not; based on the majority of my experience being fax calls from a Telecom landline --> a VFX line.

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cisconz

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Reply # 171776 17-Oct-2008 11:29

coffeebaron:
Can you clarify this a bit more Dave? What is "both ends" i.e.
- Is T.38 only applicable if both end points are VoIP? e.g. VFX-VFX, or VFX-2talk etc

No T.38 is dependant on the ADC and DAC (i.e. ATA etc) If the ata supports t.38 and the end point (vfx dropoff to telecom/ another ata etc) supports it then it will step up.

coffeebaron:
- Is T.38 applicable with PSTN <-> VoIP. e.g. a fax call comes in from PSTN, enters say WxC, terminates on a VFX line; does the WxC PSTN gateway not kick in and convert to T.38?

T.38 Media change is invocked by the recieving end. WxC and 2talk both support it on their interconnects to the other telcos.

coffeebaron:
- Or is it the fax machine at either end that is the issues here?
I'm just trying to work out why T.38 sometimes works and some times not; based on the majority of my experience being fax calls from a Telecom landline --> a VFX line.

T.38 is done within the ATA not the fax machine.

Hmmmm

coffeebaron

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Reply # 171780 17-Oct-2008 11:46

That is my understanding of how it is suppose to work - I'm just puzzled why it often does not work, even when all those boxes are ticked :(

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