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E&M "Wink Start" is a CASr1 variant.

== Overview ==

The E&M (often called "Wink Start") variants of CASR1 are "symetrical" CASR1 variants (both sides use identical signaling and state machines, calls can be made in both directions).
* Only bit A is used (generally replicated to bit B)
** Idle ("on hook") pattern is to set bit A to 0
** "Off hook" pattern is to set bit A to 1

Summary of the "wink start" call flow:
* Caller side goes "off hook"
* Receiver side "winks" (goes "off hook" for short period of ~200ms)
* Caller side detects "wink" and sends digits
* Receiver side receives digit (sends another "wink" in "Wink-start-ack" variant)
* Receiver side eventually goes "off hook"
Call termination:
* One side goes "on hook"
* Other side confirms with "on hook" too

== Supported E&M variants ==

TelcoBridges provides a E&M-compatible CAS script. You can find general documentation about CASR1 scripts in Toolpack in the following page:
[[CASr1_scripting]].

The E&M script provided by TelcoBridges already supports the following variants:
* Delay start
* Wink-start
* Wink-start-ack

Note that since this is a script, other variants may easily be added to this script by TelcoBridges or even by the user, with some knowledge of the LUA programming language.


== Configuration ==

=== Choosing variant ===
To specify a script to use E&M, you MUST specify one of the following:
<pre>
CasR1.Variant = CasR1.VariantTypes.DELAY_START
CasR1.Variant = CasR1.VariantTypes.WINK_START
CasR1.Variant = CasR1.VariantTypes.WINK_START_ACK
</pre>

Depending if you want to use 0, 1 or 2 winks.


=== Configuring exchange of ANI/DNIS ===
* ANI stands for "Automic Number Identification" (or "calling number).
* DNIS stands for "Dialed Number Identification Service" (or "called number").

In the E&M variants, ANI (calling number) is optional, while DNIS (called number) is mandatory.

==== Detection of ANI and/or DNIS ====
Configuration of reception/transmission of ANI/DNIS is controlled by the following variables:
<pre>
	ANI = {
		prefix = "",
		suffix = "",
		expected_digits = 0,
		inter_digit_timeout = 0,
	},
	
	DNIS = {
		prefix = "*",
		suffix = "#",
		expected_digits = 0,
		inter_digit_timeout = 0,
	},
</pre>

* ANI/DNIS may be surrounded by separator digits (most of the time "KP" and "ST" MFR1 tones).
** Prefix/suffix are automatically added by the script when the digits are being sent
** Prefix/suffix are detected by the script and removed from the collected digits before being reported to the application as calling/called numbers
* Expected number of digits is generally used in cases where no prefix/suffix are used, but instead a well-known (and fixed) number of digits are expected to be received
* The inter-digit timeout allows to declare ANI/DNIS complete after a delay without receiving subsequent digits. This is generally used with prefix/suffix separators are not used.

==== Enabling/disabling usage of ANI ====
To enable detection of ANI, enable one of the 3 detection methods above (prefix/suffix, expected number of digits, or inter-digit timeout).

If none is used, ANI won't be sent or received by the script.



== Subvariants ==
Here are the differences between the subvariants:

=== Delay Start ===
There's no wink before receiving ANI/DNIS. Instead, a fixed delay is inserted after going "off hook" and before sending the first digit.
The following script constant defines that delay, and may be modified:
<pre>
	OUTGOING_DELAY_TIMEOUT	= 500
</pre>

=== Wink Start ===
There's 1 wink before exchanging ANI/DNIS. In that variant, ANI/DNIS tones will only be sent after detecting a Wink from the remote side.
A Wink will be sent after detecting a remote "off hook" (new incoming call).

Wink duration can be configured by the following script constant (in milliseconds):
<pre>
	INCOMING_WINK_DURATION 	= 200
</pre>

=== Wink Start ACK ===
There's 1 wink before receiving ANI/DNIS.
There's 1 wink after receiving ANI/DNIS.

== Detailed information about the E&M script and state machines ==
For more detailed information about how this script is implemented (various states, and options), please refer to the "e_m.lua" script provided with Toolpack.