This blog post introduces a product which I designed/developed, with following rough specifications:
• Allwinner A20 dual Core Cortex-A7 CPU • 1Gbyte DDR3 RAM • 8Gbyte eMMC • Ethernet & Wifi networking capabilities • Debian 7/8 Linux • Asterisk SIP Server • Digium Web Interface
Figure 1 SIP Server
SIP (Session Initiation Protocol) is an application layer communication protocol used to make voice / video / messaging applications. 
Especially for Home Automation market, voice communication has large user base. Especially for multi-flat apartments, typically there are a few SIP Intercom devices, and up to hundreds of SIP Clients in every house.
Figure 2 Typical Infrastructure for SIP communication in an Apartment/Residence
In order to provide a reliable digital communication, SIP protocol is widely used. A SIP Server is used to manage connections between subscribers, a Touch Panel or a Mobile Phone.
Major Requirements for this project was:
• Extremely Low cost • Use open-source components • Handle basic SIP management • Easy commissioning tool
In order to comply with above requirements, I decided to reuse my existing ARM based PCBA design, and ported Debian 8 to it.
In order to handle basic SIP management, I installed Asterisk SIP server, and customized Digium Web interface.
You can see photos below for the final product:
Figure 3 ARM Linux SIP Server
As seen in above photos, since I reused my ARM based PCBA, the final product had many more hardware interfaces than found in typical SIP servers in the market. Such as:
• HDMI • USB • KNX • 3x Dry Contact Input • 3x Output Relays
During my work as R&D / Project Manager, I developed this Asterisk based Arm Linux SIP server between 2013-2014.
Hundreds of thousands of private homes / apartments / buildings / offices are using these products with a reliable SIP communication for 7 years without any issue.