Fax Operation

		Fax Operation

You should use the fax software supplied with your modem to send and receive faxes. Consult the documentation or on-line help associated with that software for more information. This chapter gives a brief overview of fax operation and the acceptable fax commands.

In addition to operating as a fully featured data modem, the modem also has the capability to handle the transmission and reception of facsimile information. To provide this functionality, it has to be able to communicate with a group 3 fax machine anywhere in the world.

Communication with the remote fax machine is performed in a similar fashion to that used for data transmission. However, the modulation schemes used are half duplex V.27ter, V.29 and V.17 unlike the full duplex modulations used for data transmission. V.29 is the more common, but the modem will automatically fall back to the slower V.27ter standard if the line quality is poor. V.17 is a higher speed standard which is becoming more common.

Also required in fax transmission is session management. This is an agreed procedure for exchanging information during the call. The T.30 standard that specifies V.21 channel 2 for negotiation and HDLC (High-level Data Link Control) for data transfer provides this function. There are five consecutive phases to the T.30 procedure. Phase A uses tone signalling to perform call establishment. Phase B is the parameter negotiation phase using V.21. The actual message transfer is performed with V.17, V.29 or V.27ter during Phase C. Phase D again uses V.21 but this time for message administration before disconnection in the final phase, E.

Another ITU-T standard, T.4, defines the format of the image data. It also defines the means of compressing the data prior to transmission.

In addition to communicating with the remote fax machine, the modem also has to have a means of communicating these images to and from the user of the modem. The modem provides two sets of commands for communicating with fax software.

Class 1 describes the physical and data link layers for dialling, waiting, signalling and data formatting. It requires the host DTE software to handle the T.30 session management and T.4 image data handling.

Class 2 includes the T.30 session management handling in the modem. This relieves the host DTE software of this task but it must still handle the T.4 image data handling.

Using fax commands

Fax commands are typically used in one of three ways, as shown below:

+F<cmd>= Select command option :

Requests the modem to select an option for the command, <cmd>, entered. For example: +FCLASS=0 <Return> will select the data mode option.

+F<cmd>? Report active configuration :

This command requests the modem to report its current active configuration for the command, <cmd>, entered. For example:

+FCLASS? <Return>

A typical response might be 2 to indicate that fax Class 2 is enabled.

+F<cmd>=? Report operating capabilities :

This command is used to display the available parameters for the command, <cmd>, entered. For example:

+FCLASS=? <Return>

The response would be 0, 1, 2.

Fax Class 1 commands

This interface complies with the approved EIA 578 standard. The serial interface supports 19200 bps with flow control using XON/XOFF or RTS/CTS. Commands are entered with the AT prefix as with other modem commands and executed after pressing <Return>. Briefly, the following commands are provided.

+FCLASS Select fax class :

This command is used to select between fax and data modes.

+FCLASS=0 selects data mode. +FCLASS=1 selects fax Class 1. +FCLASS=2 selects fax Class 2.

+FAE Data/fax automatic answer :

The +FAE=0 command restricts the automatic answering facility within the modem to accept fax calls only.

+FAE=1 allows the modem to determine whether an incoming call is fax or data, and answer accordingly.

+FTS Stop transmission and wait :

The +FTS=n command is used to inform the modem to stop transmitting and wait for the period specified by the n. Each n is 10 milliseconds. Therefore, a value of 5 equates to 50 milliseconds. After this interval, the OK message is returned.

If this command is issued while the modem is on hook, the ERROR message will be returned.

+FRS Receive silence :

This command sets the period that the modem will wait when it detects silence on the line before returning the OK message. The command takes the form of +FRS=n where n equals 10 millisecond intervals. For example, +FRS=4 <Return> will tell the modem to wait for 40 milliseconds The command may be aborted by sending any character from the DTE. In this case, the OK message is returned.

If this command is issued while the modem is on hook, the ERROR message will be returned.

+FTM Transmit data :

The +FTM=n command is used to instruct the modem to transmit data at the modulation defined. See modulations definition table.

+FRM Receive data :

The +FRM=n command is used to instruct the modem to enter receive mode at the modulation defined. See modulations definition table.

+FTH Transmit data with HDLC framing :

The +FTH=n command is used to instruct the modem to transmit data using the HDLC protocol at the modulation defined. See modulations definition table.

+FRH Receive data with HDLC framing :

The +FRH=n command is used to instruct the modem to enter receive mode using the HDLC protocol at the modulation defined. See modulations definition table.

**Modulation definitions**
n = 3	selects V.21, channel 2, 300 bps
n = 24	selects V.27ter 2400 bps
n = 48	selects V.27ter 4800 bps
n = 72	selects V.29 7200 bps
n = 73	selects V.17 7200 bps long train
n = 74	selects V.17 7200 bps short train
n = 96	selects V.29 9600 bps
n = 97	selects V.17 9600 bps long train
n = 98	selects V.17 9600 bps short train
n = 121	selects V.17 12000 bps long train
n = 122	selects V.17 12000 bps short train
n = 145	selects V.17 14400 bps long train
n = 146	selects V.17 14400 bps short train

Fax Class 2 commands

These are the commands used by the fax software supplied with the modem during transmission and reception of faxes. The following commands are supported.

More than one command may be entered on one line in a similar manner to that used when entering data commands. In addition, the semi-colon ";" character may be used as an inter-command separator.

While in fax mode, the DTE-to-modem port speed is 19200 bps. XON/XOFF and RTS/CTS flow control is available only for the DTE-to-modem direction. There is no provision for data flow control from modem to DTE.

Action commands
D Dial :

The D command is used to originate a call in the same manner as for data operation.

A Answer :

The A command is used to answer a call in the same manner as for data operation.

+FDT Data transmission :

The +FDT command prefixes Phase C data transmission. When the modem is ready to accept Phase C data, it issues the negotiation responses and the CONNECT message.

+FET Transmit page punctuation :

This command is used to punctuate document/page transmission after one or more +FDT commands have been issued. The command must be sent within the time-out period specified by the +FPHCTO command after sending Phase C data. If this is not the case, the modem will terminate the page and document transmission.

The remote fax station should respond to a +FET command with the +FPTS response.

+FDR Begin or continue Phase C receive data :

The +FDR command is used to initiate the transition to Phase C data reception after answering or dialling or after a document/page is received. When the modem is ready to transfer data, it issues a CONNECT message. If there is no more data available to transfer, the OK message is returned.

+FK Session termination :

Upon receipt of the +FK command, the modem will terminate the current fax session at the next appropriate opportunity. The modem will then hang up and return the +FHNG message.

+FMFR? Identify manufacturer :

The +FMFR? command will return the modem's manufacturer identity.

+FMDL? Identify model :

The +FMDL? command will return the modem's model identity.

+FREV? Identify revision :

The +FREV? command will return the modem's model revision.

Modem responses
+FCON Fax connection response :

The +FCON response indicates connection to a fax machine.

+FDCS Report current session capabilities :

This response indicates the current session parameters. You may see this response after +FDT or +FDR commands have been issued.

For an explanation of the sub-parameters attached to this response, see the end of this chapter.

+FDIS Report remote session capabilities :

This response reports the remote fax station identification, capabilities and intentions. It is returned in response to the A, D, +FDT and +FDR commands.

For an explanation of the sub-parameters attached to this response, see the end of this chapter.

+FCFR Indicate confirmation to receive :

The modem returns this response when it is ready to receive Phase C data from the remote fax station. It is returned in response to the +FDR command.

+FTSI Report the transmit station ID :

This response indicates the received transmit station identification, if any. It is returned in response to the A, D, +FDT and +FDR commands.

+FCSI Report the called station ID :

This response reports the received called station identification, if any. It is returned in response to the A, D, +FDT and +FDR commands.

+FPTS Receive/Transmit page transfer status :

The +FPTS response is generated by the modem at the end of Phase C data reception. The format of the response indicates the post page response and line count.

The response can be set using the session parameter +FPTS=.

+FET Post page message response :

The +FET response is returned by the modem at the end of Phase C reception, on receipt of the post page message from the transmitting station. It is returned in response to the +FDR command.

+FHNG Call termination with status :

This response indicates that the call has been terminated. The cause for the termination is reported as a code number. See the table at the end of the chapter for the meaning of these codes.

Session parameters
+FDCC Modem capabilities parameters :

There are a number of parameters used to control the operation of a fax session. To view the parameters and their available options, the +FDCC=nn command would be issued. A list of all parameters is given at the end of this chapter. When +FDCC is modified, the modem copies the new value into +FDIS.

+FDIS Current session parameters :

This command is used to view the current fax session capabilities for the parameter supplied. A list of all sub-parameters is given at the end of this chapter.

+FDCS Current session results parameters :

The +FDCS reports the current fax session parameters negotiated. The transmitting modem generates this information which may be viewed by the user at the DTE. The results are issued during execution of +FDR or +FDT commands or in direct response to a +FDCC=nn command. A list of all sub-parameters is given at the end of this chapter.

+FLID Local ID string :

This command is used to set the local identifying information stored within the modem. This allows the remote system to identify the calling station. The string may be up to 20 ASCII characters in length.

+FCR Capability to receive :

The +FCR command is used to select when the modem will or will not receive message data.

+FCR=0 indicates that the modem will not receive data.

+FCR=1 indicates that the modem will receive data.

+FAA Adaptive answer :

The +FAA=0 command restricts the modem to answer as instructed by the +FCLASS command.

The +FAA=1 command allows the modem to answer an incoming call and automatically determine whether to act as a fax Class 2 or a data modem.

+FBUF? Buffer size (read only) :

The +FBUF command is used to determine the characteristics of the modem's data buffer. The response indicates four values in the following order: total buffer size, XOFF threshold, XON threshold, current buffer byte count.

+FCQ Copy quality checking :

The modem returns +FCQ=0 which indicates it does no quality checking. The modem will generate copy quality OK (MCF) responses to complete pages and set +FPTS=1.

+FPHCTO Phase C response time-out :

The +FPHCTO command is used to instruct the modem how long to wait for a command upon completion of data when transmitting in Phase C. The valid values are in the range 0-255 in 100 millisecond units. The default is 30. When this timeout period expires, the modem will presume that no more documents/pages are to be sent and will issue the T.30 "end of page" response to the remote station.

+FAXERR Fax error value (read only) :

This message is issued by the modem at the end of an on-line fax session. The attached value indicates the cause of the hang up.

+FBOR Phase C data bit order :

The +FBOR command determines the order in which data bits are transmitted between the DTE and the modem and between the modem and the PSTN.

+FBOR=0 selects direct bit order where the first bit of a byte sent to the modem is the first bit sent down the PSTN.

+FBOR=1 selects reverse bit order where the first bit of a byte sent to the modem is the last bit sent down the PSTN.

This command controls Phase C data during execution of the +FDT or +FDR commands.

+FPTS Page transfer status :

The +FPTS= parameter is set by the receiving modem after Phase C data reception and by the transmitting modem in response to the status reported by the receiver. The value is reported in the +FPTS response.

Sub-parameter codes
The +FDIS and +FDCS commands provide a response using a sub-parameter list. Ranges of values for each parameter may be reported within parentheses. For example, the modem might respond to +FCC=? with (0,1), (0-3), (0-2), (0), (0-1), (0), (0), (0-7).

An example of the +FDIS command usage is:

+FDIS=0, 3, 0, 2, 0, 0, 0, 1

which is interpreted as:

VR=0	Vertical resolution 98 dpi
BR=3	Bit rate 9600 bps
WD=0	Page width 1728 pixels
LN=2	Page length unlimited
DF=0	Data compression 1-D modified Huffman coding
EC=0	No error correction
BF=0	No binary File transfer
ST=1	5 ms scan time/line

Hangup Status Codes
Code Cause Description
0-9 Call Placement and Termination
0 Normal and proper end of connection.
1 Ring detect without successful handshake.
2 Call aborted, from +FK or AN.
3 No Loop Current.
10-19 Transmit Phase A & Miscellaneous Errors
10 Unspecified Phase A error.
11 No Answer (T.30 T1 timeout).
20-39 Transmit Phase B Hang-up Codes
20 Unspecified Transmit Phase B error.
21 Remote cannot receive or send.
22 COMREC error in transmit Phase B.
23 COMREC invalid command received.
24 RSPEC error.
25 DCS sent three times without response.
26 DIS/DTC received 3 times; DCS not recognised.
27 Failure to train at 2400 bps or + FMINSP value.
28 RSPREC invalid response received.
40-49 Transmit Phase C Hang-up Codes
40 Unspecified Transmit Phase C error.
43 DTE to DCE data underflow.
50-69 Transmit Phase D Hang-up Codes
50 Unspecified Transmit Phase D error.
51 RSPREC error.
52 No response to MPS repeated 3 times.
53 Invalid response to EOP repeated 3 times.
54 No response to EOP repeated 3 times.
55 Invalid response to EOP.
56 No response to EOP repeated 3 times.
57 Invalid response to EOM.
58 Unable to continue after PIN or PIP.
70-89 Unspecified Receive Phase B error.
70 Normal and proper end of connection.
71 RSPREC error.
72 COMREC error.
73 T.30 T2 timeout, expected page not received.
74 T.30 T1 timeout, after EOM received.
90-99 Receive Phase C Hang-up Codes
90 Unspecified Receive Phase C error.
91 Missing EOL after 5 seconds.
92 Unused code.
93 DCE to DTE buffer overflow.
94 Bad CRC or frame (ECM or BFT modes).
100-119 Receive Phase D Hang-up Codes
100 Unspecified Receive Phase C error.
101 SPREC invalid response received.
102 COMREC invalid response received.
103 Unable to continue after PIN or PIP.
120-255 Reserved Codes

**Hangup Status Codes**
Code	Cause Description
0-9	Call Placement and Termination
0	Normal and proper end of connection.
1	Ring detect without successful handshake.
2	Call aborted, from +FK or AN.
3	No Loop Current.
10-19	Transmit Phase A & Miscellaneous Errors
10	Unspecified Phase A error.
11	No Answer (T.30 T1 timeout).
20-39	Transmit Phase B Hang-up Codes
20	Unspecified Transmit Phase B error.
21	Remote cannot receive or send.
22	COMREC error in transmit Phase B.
23	COMREC invalid command received.
24	RSPEC error.
25	DCS sent three times without response.
26	DIS/DTC received 3 times; DCS not recognised.
27	Failure to train at 2400 bps or + FMINSP value.
28	RSPREC invalid response received.
40-49	Transmit Phase C Hang-up Codes
40	Unspecified Transmit Phase C error.
43	DTE to DCE data underflow.
50-69	Transmit Phase D Hang-up Codes
50	Unspecified Transmit Phase D error.
51	RSPREC error.
52	No response to MPS repeated 3 times.
53	Invalid response to EOP repeated 3 times.
54	No response to EOP repeated 3 times.
55	Invalid response to EOP.
56	No response to EOP repeated 3 times.
57	Invalid response to EOM.
58	Unable to continue after PIN or PIP.
70-89	Unspecified Receive Phase B error.
70	Normal and proper end of connection.
71	RSPREC error.
72	COMREC error.
73	T.30 T2 timeout, expected page not received.
74	T.30 T1 timeout, after EOM received.
90-99	Receive Phase C Hang-up Codes
90	Unspecified Receive Phase C error.
91	Missing EOL after 5 seconds.
92	Unused code.
93	DCE to DTE buffer overflow.
94	Bad CRC or frame (ECM or BFT modes).
100-119	Receive Phase D Hang-up Codes
100	Unspecified Receive Phase C error.
101	SPREC invalid response received.
102	COMREC invalid response received.
103	Unable to continue after PIN or PIP.
120-255	Reserved Codes