Recent Posts

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RTP pass-through mode in Asterisk

October 23, 2009

What is RTP pass-through mode in Asterisk? The speech for VoIP calls uses RTP (Real Time Protocol) to get from one end to the other and it is compressed using one of the many speech compression codecs available. Commonly used codecs include G.711 and G.729. When you call someone through an Asterisk PBX, there will be […]

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How can an Asterisk IP-PBX benefit my business?

August 23, 2009

In a Nutshell: The benefits of upgrading to an Asterisk based IP-PBX

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High Availability and Failover options for SIP and Asterisk

May 29, 2009

Overview What’s the disaster we are trying to avoid? The assumed scenario is this: Some kind of centralised VoIP service is being offered to a number of users; the service operates on servers located at a data centre or office and the users each have a SIP client device, such as an IP phone, that […]

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SIP Subscribe/Notify and Asterisk Hints Explained

March 6, 2009

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 in the SIP protocol document RFC 3265. Basically, it works like […]

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How do you choose the right VoIP Service Provider?

March 4, 2009

VoIP Service Providers – the core services on offer Business and home users all have to choose from roughly the same pool of companies providing VoIP services, but the things that they are looking for may not completely overlap. Let’s consider a few of the more important services provided. Cheap calls Why use VoIP? Answer […]

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Configuring IP phones as Asterisk PBX extensions

February 22, 2009

A first look at the SIP.CONF file It is assumed here that your IP phones all use the SIP protocol to register, make and receive calls. Before an IP phone can connect to Asterisk and operate as an extension, it is necessary to configure user account details on the Asterisk server. The configuration file of […]

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About IP Packet Communications – TCP and UDP

February 20, 2009

Devices communicate data to other devices on the Internet using certain recognised protocols that involve routing and transmission of packets of data to a remote device identified by an IP addresses. The most widely used protocols on the Internet are TCP and UDP. The differences between these two protocols are of a highly technical nature […]

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What is NAT?

February 20, 2009

What is NAT? NAT stands for Network Address Translation. Many devices sold as Firewalls or Routers are actually combined Firewall, Router and NAT device in one box. NAT is the mechanism that allows you to have many PC’s on your LAN all connected to the Internet through a single external IP address. When one of […]

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What does it cost to make calls with a VoIP phone?

February 13, 2009

How can you make calls for free with VoIP? The cost of a telephone call Just in case you are wondering, you can’t buy a VoIP phone, plug it in, set it up and start calling any number you like for free. It is not that simple – in fact, when you start looking into […]

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Configuring and Using SIP Domains in Asterisk

January 28, 2009

What are SIP Domains? SIP requests delivered to a Proxy server or other SIP device must contain details of valid destinations and end-points that are to be reached or which are to receive responses. The address of a SIP device is generally referred to as its URI (Uniform Resource Identifier) – it has to uniquely […]

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