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--- Shared Line Appearances ---------------------------------
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INTRODUCTION

The "SLA" functionality in Asterisk is intended to allow a setup that emulates
a simple key system.  It uses the various abstraction layers already built into
Asterisk to emulate key system functionality across various devices, including
IP channels.
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DIALPLAN CONFIGURATION

The SLA implementation can automatically generate the dialplan necessary for
basic operation if the "autocontext" option is set for trunks and stations in
sla.conf.  However, for reference, here is an automatically generated dialplan
to help with custom building of the dialplan to include other features, such as
voicemail:

[line1]
exten => s,1,SLATrunk(line1)

[line2]
exten => s,2,SLATRUNK(line2)

[sla_stations]
exten => station1,1,SLAStation(station1)
exten => station1_line1,hint,SLA:station1_line1
exten => station1_line1,1,SLAStation(station1_line1)
exten => station1_line2,hint,SLA:station1_line2
exten => station1_line2,1,SLAStation(station1_line2)

exten => station2,1,SLAStation(station2)
exten => station2_line1,hint,SLA:station2_line1
exten => station2_line1,1,SLAStation(station2_line1)
exten => station2_line2,hint,SLA:station2_line2
exten => station2_line2,1,SLAStation(station2_line2)

exten => station3,1,SLAStation(station3)
exten => station3_line1,hint,SLA:station3_line1
exten => station3_line1,1,SLAStation(station3_line1)
exten => station3_line2,hint,SLA:station3_line2
exten => station3_line2,1,SLAStation(station3_line2)
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TRUNKS

For the trunk side of SLA, the only channels that are currently supported are
Zap channels.  Support for IP trunks is planned, but not yet implemented.

Be sure to configure the trunk's context to be the same one that is set for the
"autocontext" option in sla.conf if automatic dialplan configuration is used.

If the dialplan is being built manually, ensure that calls coming in on a trunk
execute the SLATrunk() application with an argument of the trunk name.
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STATIONS

Currently, the only channel driver that has all of the features necessary to
support an SLA environment is chan_sip.  Here are some hints on configuring
a SIP phone for use with SLA:

1) Add the SIP channel as a [station] in sla.conf.

2) Configure the phone in sip.conf.  If automatic dialplan configuration was
   used by enabling the "autocontext" option in sla.conf, then this entry in
   sip.conf should have the same context setting.

3) On the phone itself, there are various things that must be configured to
   make everything work correctly:

   Let's say this phone is called "station1" in sla.conf, and it uses trunks
   named "line1" and line2".

   a) Two line buttons must be configured to subscribe to the state of the
      following extensions:
        - station1_line1
        - station1_line2

   b) The line appearance buttons should be configured to dial the extensions
      that they are subscribed to when they are pressed.

   c) If you would like the phone to automatically connect to a trunk when it
      is taken off hook, then the phone should be automatically configured to
      dial "station1" when it is taken off hook.
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