Steps to fix the best codec for sending faxes

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Hopefully, if you have the most suitable codec for sending faxes on your system, this blog post can help you fix the problem. G711, also known as uncompressed codec. Make sure your VoIP fax connection (the line you will next use to send your fax) is set to G711, which is an uncompressed codec.Reduce the transmission speed near the fax machine.Turn off the ECM (error correction mode).

When configuring the fax mode, you need to pay attention to the choice of sound for codecs.

Which codec is used for fax?

38. A widely used codec for enabling real-time transmission of facsimile data over Voice over Internet Protocol (VoIP) networks. Faxes cannot be transmitted over a data network with the same concept as an analog connection.

When choosing voice codecs, you should always adhere to the following rules:

T.38 fax must be fully compliant using all detection codecs. At least one audio must have a codec. At least one of the commonly chosen codecs must be supported by your own H or 323 SIP network.
Note that the initial T.38 fax settings are pressed and held. Some fax operations can be performed in the new audio mode before switching to T.38. If you are using codecs other than G.711-ulaw and G.711-Alaw, CED cng fax tones also cannot be transmitted or recognized. For this reason, we recommend that you use the G.711 codecs even if you are using T.38 faxes.
To ensure that the generation of the CNG tone when sending the second fax and T.38 audio is definitely doneFor a G.711-ulaw or G.711-Alaw deck, you can use the T .38 parameter after … T seconds. 38 use small fax with delay (0-2 sec.).
Audio fax (fax via G.711 codec) is saved only when using the G.711-ulaw or G.711-Alaw codecs. Therefore, at least one of these codecs must be selected and supported by one SIP or H.323 network.
To prevent sending or receiving faxes in audio mode, anyone can disable the G.711-ulaw and G.711-Alaw codecs. If possible, this is because your SIP or H.323 provider supports one of the other codecs.
For compatibility with Audiofax when using codecs other than G.711-ulaw and G.711-Alaw, it is strongly recommended to use G.711-ulaw and G.711-Alaw when set to “Highest”. Correct reboot of G vers. 711-ulaw or G.711-Alaw on every call using another popular music codec is not guaranteed in Fax Voip FSP application. Loading = “lazy”

How do I send a fax using VoIP?

Because senders cannot operate over VoIP lines, families need an analog telephone adapter (ATA) to connect them to a VoIP connection. Popular VoIP providers offer faxing as part of their VoIP service, often at an incredible additional cost.

There is no doubt that there are great benefits to the introduction of VoIP products (eg Asterisk PBX), and of course there are many people who would enjoy using a VoIP PBX trunk instead of traditional telephone lines.

But when using VoIP PBX, a person may find that the fax is also not working if he remembers that he was working on an analog phone that was disconnected.

Got it: do faxes work on PBX / VoIP lines as perfectly as current analog / Pbx lines?
Answer: mostly!

Fax numbers do not work as well in a VoIP environment as they do on an “old” phone line. FAX was designed for analog networks and cannot simply be transmitted over a digital VoIP network.

The reasons are different: from the codecs used by VoIP, which are supposed to compress voice and at the same time save bandwidth and which distort the transmission of the modems / faxes used, to the fact that the signal is repeatedly converted along the caller-called path, and Pbx -Voip improves more conversion points, making it more expensive to send / receive faxes.

Remember: OIt is important to understand that each processing step introduces some signal distortion, which is invisible to the voice, but for some reason not to the fax: and when sending faxes, the quality of the signal line is very important!

In this series, I’ll try to give you some tips for improving fax quality in a VoIP environment.

Note. I will go into detail about Asterisk PBXs in this article, but the same observations apply to other types of Voip PBXs.

This is how fax works
To get to know you better, we have some tips for using the fax function. When sending faxes, two devices are connected to transmit more pages of images.

Pages are converted to images, and the image is modified in the bitstream that is transmitted during the phone call attempt: the called device ends this target stream and converts everything back to images.

In order to transmit a bit stream with a phone call, which allows for mostly voice / sound, the line must be modulated, which means that all involved bits necessarily convertinto an audio signal, which can be sent from the other end to convert the received signal back into a stream of sections and therefore images in it.

Clearer: Components are converted to audio, and so on, and sent through an audio phone call. A device that recognizes melodies (a fax machine is a machine) is able to understand this “noise” in the bitstream.

Disclaimer: This is the easiest way to deal with the older and most popular type of fax machine: new fax machine parts that differ in type (eg ISDN fax machine) but are very rare. Here we are going to discuss only the older types of faxes.

What is the most common encoding for voice?

In particular, this LPC-based Code Excited Linear Prediction (CELP) code is the new and most widely used speech coding scheme, which is used, for example, in each of our GSM standards.

Avoid difficult times!
If possible, keep a separate legacy analog line on your phone system that you primarily use with your fax machine, connect directly to the fax machine, or use online fax support. The associated costs are very low and help protect us from anger… In some cases, this is the last resort for reliable faxing.

This decision is not a solution, I know, but …… it’s not an option on the way to an assessment….

Codec
Codec (short for codec) is the way in which an analog signal associated with a voice is encoded into bits and vice versa. There are many types of codecs that differ from each other and use the quality of the bandwidth (bytes / sec.).

Some codecs are usually incompatible with facsimile signals: that is, g729 is indeed a compressed bandwidth efficient codec, although it is indeed incompatible with broadcasts.

In a good VoIP system with unique fax paths, you should never use these types of compressed codecs. If you want fax to be integrated into your system, you just need to use g711a and g711u: this type uses more bytes per second due to codes, but becomes fully fax compatible.

The range / codec associated with the rating is quite large if the Voip system uses multiple connections It doesn’t matter, but it doesn’t matter or maybe not the path on the LAN (for example, the g711 codec family does indeed use 64KB / s bandwidth). LAN 1 Gbps).

So this first step is to make sure that at each of the steps (call segments) involved in what I would say, the caller’s path is using the most appropriate fax compatible codec.
those. Trunk – Pbx Voip ATA – An analog gateway connected to a fax machine.

It is better to use only one type of codec (g711a or g711u) for all name branches, in order to avoid translating the codecs on each of our involved devices (each codec translation introduces distortion and delays separate ones).

In asterisks you can name the codec that will be used in future commands.

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With the order, we can buy all channels or segments that currently do not contain errors in the Asterisk PBX.

Usually there were two for calls: each main line – Pbx Voip and Pbx Voip – Analog Gateway, which are connected to a fax machine.

Next command lineallows you to find the codecs used in each segment, Show

Is T 38 a codec?

Fax T.38 works with any audio codec. You must select at least one audio codec. At least one of the specific codecs must be supported by your SIP as well as H.

 main channel

> decisive SIP send channel / sip.messagenet.it-0000021câ € .. (GSM)Recording format:native formats: slinReading format: ulawWriteTranscode: Yes (slide) -> (GSM)ReadTranscode: Yes (GSM) -> (Slin) -> (ulaw)...

This layer tab uses the GSM codec (string NativeFormats: (gsm)): terrible even for faxes!

You can force the codec to return with the following SIP definitions marked with asterisks.