* The SMS application
---------------------
SMS() is an application to handles calls to/from text message capable phones and 
message centres using ETSI ES 201 912 protocol 1 FSK messaging over analog calls.

Basically it allows sending and receiving of text messages over the PSTN. It is 
compatible with BT Text service in the UK and works on ISDN and PSTN lines. It is 
designed to connect to an ISDN or DAHDI interface directly and uses FSK so would 
probably not work over any sort of compressed link (like a VoIP call using GSM codec).

Typical applications include:-

1. Connection to a message centre to send text messages - probably initiated via the 
   manager interface or "outgoing" directory
2. Connection to an POTS line with an SMS capable phone to send messages - probably
   initiated via the manager interface or "outgoing" directory
3. Acceptance of calls from the message centre (based on CLI) and storage of 
   received messages
4. Acceptance of calls from a POTS line with an SMS capable phone and storage of
   received messages

* Arguments to sms():

- First argument is queue name
- Second is options:
 a: SMS() is to act as the answering side, and so send the initial FSK frame
 s: SMS() is to act as a service centre side rather than as terminal equipment

- If a third argument is specified, then SMS does not handle the call at all,
  but takes the third argument as a destination number to send an SMS to
- The forth argument onward is a message to be queued to the number in the
  third argument. All this does is create the file in the me-sc directory.
  If 's' is set then the number is the source
  address and the message placed in the sc-me directory.

All text messages are stored in /var/spool/asterisk/sms
A log is recorded in /var/log/asterisk/sms

There are two subdirectories called sc-me.<queuename> holding all
messages from service centre to phone, and me-sc.<queuename> holding all
messages from phone to service centre.

In each directory are messages in files, one per file, using any filename not
starting with a dot.

When connected as a service centre, SMS(s) will send all messages waiting in
the sc-me-<queuename> directory, deleting the files as it goes. Any
received in this mode are placed in the me-sc-<queuename> directory.

When connected as a client, SMS() will send all messages waiting in the
me-sc-<queuename> directory, deleting the files as it goes. Any received in
this mode are placed in the sc-me-<queuename> directory.

Message files created by SMS() use a time stamp/reference based filename.

The format of the sms file is lines that have the form of key=value
Keys are :

oa	Originating Address
	Telephone number, national number if just digits
	Telephone number starting with + then digits for international
	Ignored on sending messages to service centre (CLI used)
da	Destination Address
	Telephone number, national number if just digits
	Telephone number starting with + then digits for international
scts	Service Centre Time Stamp
	In the format YYYY-MM-DD HH:MM:SS
pid	Protocol Identifier (decimal octet value)
dcs	Data coding scheme (decimal octet value)
mr	Message reference (decimal octet value)
ud	The message (see escaping below)
srr	0/1 Status Report Request
rp	0/1 Return Path
vp	mins validity period

Omitted fields have default values.

Note that there is special format for ud, ud# instead of ud= which is followed
by raw hex (2 characters per octet). This is used in output where characters
other than 10,13,32-126,128-255 are included in the data. In this case a comment (line
starting ;) is added showing the printable characters

When generating files to send to a service centre, only da and ud need be
specified. oa is ignored.

When generating files to send to a phone, only oa and ud need be specified. da is ignored.

When receiving a message as a service centre, only the destination address is
sent, so the originating address is set to the callerid.

EXAMPLES

The following are examples of use within the UK using BT Text SMS/landline
service.

This is a context to use with a manager script.

[smsdial]
; create and send a text message, expects number+message and
; connect to 17094009
exten => _X.,1,SMS(${CALLERIDNUM},,${EXTEN},${CALLERIDNAME})
exten => _X.,n,SMS(${CALLERIDNUM})
exten => _X.,n,Hangup

The script sends

	action: originate
	callerid: message <from>
	exten: to
	channel: Local/17094009
	context: smsdial
	priority: 1

You put the message as the name of the caller ID (messy, I know), the
originating number and hence queue name as the number of the caller ID and the
exten as the number to which the sms is to be sent. The context uses SMS to
create the message in the queue and then SMS to communicate with 17094009 to
actually send the message.

Note that the 9 on the end of 17094009 is the sub address 9 meaning no sub
address (BT specific). If a different digit is used then that is the sub
address for the sending message source address (appended to the outgoing CLI
by BT).

For incoming calls you can use a context like this :-

[incoming]
exten => _XXXXXX/_8005875290,1,SMS(${EXTEN:3},a)
exten => _XXXXXX/_8005875290,n,System(/usr/lib/asterisk/smsin ${EXTEN:3})
exten => _XXXXXX/_80058752[0-8]0,1,SMS(${EXTEN:3}${CALLERIDNUM:8:1},a)
exten => _XXXXXX/_80058752[0-8]0,n,System(/usr/lib/asterisk/smsin ${EXTEN>:3}${CALLERIDNUM:8:1})
exten => _XXXXXX/_80058752[0-8]0,n,Hangup


In this case the called number we get from BT is 6 digits (XXXXXX) and we are
using the last 3 digits as the queue name.

Priority 1 causes the SMS to be received and processed for the incoming call.
It is from 080058752X0. The two versions handle the queue name as 3 digits (no
sub address) or 4 digits (with sub address). In both cases, after the call a
script (smsin) is run - this is optional, but is useful to actually processed
the received queued SMS. In our case we email them based on the target number.
Priority 3 hangs up.

If using the CAPI drivers they send the right CLI and so the _800... would be
_0800...

