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There are several aspects to using more than one FAX modem with PMDF-FAX: specifying the modems to use, whether or not the modems are of the same type (i.e., supported by the same driver), and scheduling of delivery jobs to optimize the use of the available modems. This section attempts to address each of these issues.
37.6.3.1 Specifying the FAX Modems to Use
The G3_TO_FAX and FAX_TO_DATA channel option FAX_MODEM is used to
specify the device name associated with the modem or modems to use for
that channel. This option may specify either a physical device name
such as TTA1:, LTA100:, or TXA6:, or a logical name such as
PMDF_FAX_MODEM. When a logical name is used, the logical may
(iteratively) translate to one or more device names. That is, the
logical may specify a search list. In that case, each device in the
list will be tried until the channel finds a device which it can
allocate and then initialize the associated modem.
If the FAX_MODEM option is not specified in a G3_TO_FAX or FAX_TO_DATA option file, then the logical PMDF_FAX_MODEM is assumed to be defined and to translate to one or more device names.
As an example, consider the case where two FAX modems attached to the lines LTA100: and LTA200: are available for use. A FAX receive process will preferentially use LTA100:. For this reason, the G3_TO_FAX channel should first always try to use LTA200: and only try to use LTA100: when LTA200: is not available (or not functioning). To set this up, define the two logical search lists,
$ DEFINE/SYSTEM FAX_MODEMS_1_2 LTA100:,LTA200: $ DEFINE/SYSTEM FAX_MODEMS_2_1 LTA200:,LTA100: |
37.6.3.2 Using Different Types of FAX Modems with the Same Channel
A given G3_TO_FAX channel may utilize different types of modems. That
is, modems which require different drivers. However, the channel must
be warned of this. This is done with the MODEM_TYPE and FAX_MODEM
channel options. The MODEM_TYPE option must be specified as
MODEM_TYPE=type-1,type-2,...,type-N |
type-1, type-2,
type-N are any of CLASS2, DEXNET200, or FAXBOX30.
For each type specified with MODEM_TYPE, there must be a corresponding
device or logical name specified with the FAX_MODEM option,
FAX_MODEM=device-1,device-2,...,device-N |
type-1 using the modem or modems specified by
device-1. If none of the devices are available or
do not respond, then the driver for type-2 will
be run using the modems specified by device-2.
This process repeats until either a working device is found or all of
the devices are exhausted. In the case of the devices being exhausted,
a second pass is made in which an attempt is made to have any FAX
receive processes release the modems they are using.
For example, if two Service Class 2 modems are attached to ports TXA5: and TXA6: and a dexNET 200 to LTA333:, then the following configuration might be used
MODEM_TYPE=CLASS2,DEXNET200 FAX_MODEM=CLASS2-MODEMS,LTA333: |
CLASS2-MODEMS is a logical search list which
translates to TXA5: and TXA6:.
The FAX_TO_DATA channel does not support the use of different modem types with the same channel. Since the process of configuring an additional FAX_TO_DATA channel is very simple, this should not prove to be a problem. |
37.6.3.3 Job Scheduling and Modem Usage
Normally, only a single immediate or periodic delivery job will process
a single outbound FAX. This means that, regardless of how many FAX
modems you have, only a single FAX modem will be used to transmit a
given FAX message, even if the message is addressed to more than one
recipient. This is the default behavior. To alter this behavior, use
the channel keywords addrsperjob and maxjobs
in conjunction with the G3_TO_FAX channel. Use addrsperjob
1 and maxjobs M where
M >= 1 is the maximum number of delivery jobs
(i.e., the maximum number of modems) to use to process any
given message. When this combination is used, the number of delivery
jobs will be whichever is the smaller of M or the
number of recipients the message is addressed to.
M should never exceed the number of available
modems. Also, be sure that the job limit for the queue in which
G3_TO_FAX jobs run is set to the number of available modems.
37.6.3.4 Frequent Delivery Retries with the BACKOFF Option
Normally, if a FAX cannot be delivered owing to a temporary error
condition (e.g., busy signal), another delivery attempt will
not be attempted until the next periodic delivery job runs as described
in Section 1.4. However, for urgent FAXes, a retry in minutes rather
than tens of minutes or hours is desired. Rather than set PMDF's
periodic delivery job interval to a small value and then adjust the
service period for each channel with the period channel
keyword, the BACKOFF mapping table and G3_TO_FAX BACKOFF channel option
may be used. With this mapping table and option, you may schedule
exactly when to run jobs to attempt redelivery of undeliverable FAXes
(e.g., make attempts every minute for the first five minutes,
then every five minutes for the next thirty minutes, etc.).
See Section 25.6 for complete details on the use of the BACKOFF
mapping table and BACKOFF channel option.
When using the BACKOFF option, be sure to set the POST_INTERVAL option to a time period less than the minimum amount of time between transmission retries called for by the BACKOFF mapping table. \
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