Asterisk SLA (Shared Line Appearances) – Part 4

Link to part 3 What is good and what is bad about the Asterisk implementation of SLA? Benefits of Asterisk Shared Line Appearances Replacement of legacy systems: The main reason for wanting to configure Shared Line Appearances in Asterisk is because the Asterisk system is replacing a traditional key and lamp telephone system. However, this … Read more


Asterisk SLA (Shared Line Appearances) – Part 3

Link to part 2 EXTENSIONS.CONF: Setting the Hints used by SLA The SIP SUBSCRIBE/NOTIFY mechanism – what it is and how it works The SIP protocol includes a standardised mechanism to allow any SIP client (an IP phone being an example of a SIP client) to monitor the state of another device. Details are provided … Read more


Asterisk SLA (Shared Line Appearances) – Part 2

Link to part 1 About the examples and conf file samples used in this article The following sections will guide you through the setup of a small Asterisk system using shared line appearances. Each step is explained to show how it works. The dial plan examples will start with a fairly simple configuration and we … Read more


Asterisk SLA (Shared Line Appearances) – Part 1

Terminology and SLA Concepts Terminology We have attempted to use the correct terminology (as recognised throughout the telephony industry) within the explanations on this web page. However, as it is so important to be clear about the meaning of the terminology used here, it seemed like a good idea to set it out explicitly at … Read more


Why bother with SLA on Asterisk?

Familiarity There are, in the business world, a huge number of legacy telephone systems that use a “key and lamp” principle of operation – so-called key telephone systems. Many small business phone systems available in the market today still use this principle of operation. They are extremely ubiquitous and a large number of users and … Read more


VoIP Gateways Explained

Basic Function of a VoIP Gateway A VoIP gateway provides the interface between the IP telephony network and the conventional public switched telephone network (PSTN). For example, a gateway can be used to link a VoIP call to a PRI-30 ISDN trunk, a BRI two channel ISDN circuit or an analogue line. In fact, a … Read more