## Understanding When To Use /n

By default, the Local channel will try to optimize itself out of the call path. This means that once the Local channel has established the call between the destination and Asterisk, the Local channel will get out of the way and let Asterisk and the end point talk directly, instead of flowing through the Local channel.

This can have some adverse effects when you're expecting information to be available during the call that gets associated with the Local channel. When the Local channel is optimized out of the call path, any Dial() flags, or channel variables associated with the Local channel are also destroyed and are no longer available to Asterisk.

We can force the Local channel to remain in the call path by utilizing the /n directive. By adding /n to the end of the channel definition, we can keep the Local channel in the call path, along with any channel variables, or other channel specific information.

For example, if we were calling a Local channel from the Dial() application, we could change:

    Dial(Local/201@devices)

...into the following line:

    Dial(Local/201@devices/n)

By adding /n to the end, our Local channel will now stay in the call path and not go away.

Lets take a look at an example that demonstrates when the use of the /n directive is necessary. If we spawn a Local channel which then performs another Dial() to a SIP channel, but we use the L() option (which is used to limit the amount of time a call can be active, along with warning tones when the time is nearly up), it will be associated with the Local channel, which is then optimized out of the call path, and thus won't perform as expected.

Here is an overview of our call flow, and the information associated with the channels:

1. SIP device PHONE_A calls Asterisk via a SIP INVITE
2. Asterisk accepts the INVITE and then starts processing dialplan logic
3. Our dialplan calls Dial(Local/2@services) - notice no /n
4. The Local channel then executes dialplan at extension 2 within the services context
5. Extension 2 within [services] then performs another Dial() to a SIP channel with the line: Dial(SIP/PHONE_B,,L(60000:450000:15000))
6. The call is then placed to SIP/PHONE_B which then answers the call.
7. The Local channel containing the information for tracking the time allowance of the call is then optimized out of the call path, losing all information about when to terminate the call.
8. SIP/PHONE_A and SIP/PHONE_B then continue talking indefinitely.

Now, if we were to modify our dialplan at step three (3) then we would force the Local channel to stay in the call path, and the L() option associated with the Dial() from the Local channel would remain, and our warning sounds and timing would work as expected.

There are two workarounds for the above described scenario:

1. Use Dial(Local/2@services/n) to cause the Local channel to remain in the call path so that the L() option used inside the Local channel is not discarded when optimization is performed.
2. Place the L() option outside of the Local channel so that when it is optimized out of the call path, the information required to make L() work is associated with the outside channel. For example:

          Dial(Local/2@services,,L(60000:45000:15000))