When should I use SLA Trunks

Hi, I am new to Asterisk and I wanted to set up SIP Trunk. I discovered that I need a SIP provider, however in Asterisk documentation, there are SLA Trunks, but I am not sure when should I use this or what is the difference between SLA trunks and trunks from providers.

Can anyone explain it to me? Or give me some good resources to learn about this?

Asterisk does not have a concept of “a SIP trunk”. Please point us to the
documentation you have been reading which tells you about SLA trunks.

Asterisk connects to SIP peers, and whether these are telephones, single-
service connections to external providers, or “trunk” connections supporting
multiple simultaneous calls, is essentially irrelevant to Asterisk (the main
thing which differs between these is usually just the authentication method).

Perhaps it would be useful for you to tell us what you want to achieve with
Asterisk, and we can advise what you will need to do to get there.


SLA Trunks: SLA stands for Shared Line Appearance. In Asterisk, an SLA trunk is a virtual trunk that allows multiple devices or extensions to share the same line appearance. This means that when a call comes in, multiple devices can ring simultaneously, and any of them can answer the call. SLA trunks are typically used in call center environments or situations where multiple users need to handle incoming calls simultaneously.
Trunks from Providers: Trunks from providers, also known as SIP trunks or VoIP trunks, are connections provided by a telecommunications company or SIP provider. These trunks allow you to connect your Asterisk server to the public switched telephone network (PSTN) or other VoIP networks. With SIP trunks, you can make and receive calls to and from external phone numbers, both landlines and mobile numbers, over the internet.

The main difference between SLA trunks and trunks from providers is their purpose and functionality. SLA trunks are used for internal call routing within an Asterisk system, allowing multiple devices to handle incoming calls. Trunks from providers, on the other hand, are used to connect your Asterisk system to external phone networks, enabling you to make and receive calls to and from the outside world.

Thank you Anthony and zzoah

my plan is to set up trunk, so that Grandstream phones, that are connected to 2 different asterisk servers, can call each other, and goal is to learn how to handle external call to Asterisk. So I guess I need VoIP provider. Thank you both for your explanations.

Also I wanted to ask, do i need to install dahdi and libpri? Because so far with Grandstream phones on one asterisk server i did not need it.

Do you know some reliable provider, that provides free trunks?

That only requires internet connectivity. Preferably you use static addresses, in which case both sides are set up as though the other were a provider that didn’t require registration. (At least one side must have a known IP address, even with registration.)

There is no need for DAHDI and libpri. As already noted, Asterisk doesn’t distiguish between “trunks” and “extensions”, and doesn’t use the former term and doesn’t use the latter in that way.

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