Equisys technical notes

Technical guidance, explanations and fixes for our products

INFO: Determining the maximum number of channels for fax broadcast use



ID: ZTN1988

This Zetafax technical note applies to:

  • Zetafax 2014 and earlier


A single Zetafax Server supports a maximum of 180 fax channels for sending and receiving faxes (e.g. 6 x 30 channel ISDN E1 lines).  This technote aims to provide information on the other factors which can impact the number of channels available on a server.

More information

There are several other factors to consider when determining the maximum number of channels which will be utilised on a single server:

Type of device

For high density use where overall throughput is a priority, Equisys recommend Brooktrout TR1034 boards.  These offload much of the processing onto the board, reducing the load on the server computer.

Number of supported boards

For high-density systems it is necessary to ensure that the required number and types of fax boards can be supported on the server computer.  Equisys (or our appointed distributor) will consult Dialogic to check that the number/type of boards being supplied will be fully supported, and the customer should also ensure that their server computer also has sufficient capacity (free slots) for these boards.  

Server specification

Fax preparation is processor and disk intensive, and to maximise throughput it is necessary to reduce the average preparation time for each fax.  A minimum specification server computer with low speed processor or low speed disk access for the shared server files will reduce throughput and so use fewer fax channels.

Whether the system has the FaxBroadcast licence add-on

Any system with high density outbound fax (say > 30 lines) should include the optional FaxBroadcast licence add-on, even if faxes are not being submitted using the FaxBroadcast client.  This increases the throughput of the server by reducing the number of status updates it gives while sending a fax

Type of faxes being sent, amount of personalisation, and number of recipients per Zetafax message  

For outbound fax broadcast use, the type of fax being sent and how the broadcast job is submitted has a large effect on the ratio between preparation and transmission time. This determines how many lines will be kept busy by the Zetafax Server.  If the job is a standard (non-personalised) page fax being sent to large numbers of people, then the average preparation time will be much shorter than the average time to dial and transmit the fax, so the number of lines used will be high.  If instead each fax is personalised, or the faxes are submitted individually (e.g. using individual embedded addressing commands), then the average preparation time will increase.  Similarly, if most fax numbers are correct and connect successfully then the average transmission time will be higher than a broadcast job where a high proportion of numbers are invalid and the system is configured so numbers are only tried once.

For example, a typical one page fax takes 30 seconds to send.  To keep 180 lines busy, then the average preparation (conversion) time must be less than 0.3 seconds – this can be determined using a test system before hardware purchase by configuring devices in “demonstration mode”. 

Equisys have tested sending concurrently with 180 fax channels, using standard (unpersonalised) faxes submitted with the FaxBroadcast client with a high success rate (ie valid fax numbers).  The Zetafax Server kept all 180 lines busy successfully.

Whether old (completed) messages are removed from the Outbox

For systems where overall throughput is a priority, it is important to tidy-up (delete) old faxes from the Outbox regularly. If instead old faxes are left in the Outbox, then the throughput will degrade over time.

For customers planning a high volume fax broadcast system, we would recommend testing with typical faxes to optimise the way they are submitted and determine the number of channels required before purchasing the hardware. Zetafax supports “demonstration mode” devices which emulate the sending process without requiring hardware.  Configuring a system with these devices then analysing preparation time and overall throughput can assist in purchasing the correct number of channels, and save costs and time overall.

Equisys is happy to assist with analysing test data, and with individual advice on how to maximise throughput.  Because of the amount of time involved in doing this, it is a chargeable service, at our standard consultancy rates.  Please contact us if you want further details about this service.


Last updated: 18th December 2013 (GW/MW)

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