Tag: asterisk
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Top reasons why VoIP calls drop
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VoIP based phone systems bring many benefits, but they also bring some problems. Not least is the annoying tendency for some calls to drop mid-way through your conversation for no obvious reason. In this article I will identify the most common reasons why a VoIP call might suddenly drop mid-way through an established call and explain how you can diagnose the cause. At the end are some pointers to the solutions for these problems. This article is…
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OpenSIPS vs Asterisk
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OpenSIPS and Asterisk are both open source projects and both are used for Voice over IP. However, they perform quite different roles, have different capabilities and different strengths and weaknesses. This article reviews how they are so different and considers what role each product can play in the infrastructure of an Internet Telephony Service Provider solution. Fundamental differences A succinct, but slightly technical, distinction between OpenSIPS and Asterisk is that OpenSIPS is essentially a SIP Proxy Server…
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Setting up shared voicemail on Asterisk – part 2
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Part 1 laid the foundations for creating and accessing a shared voicemail box. In this, part 2, I explain how the lamp on the BLF key is switched on and off to show there are messages waiting in the shared box. Note that this is separate from any existing MWI lamp used for personal voicemail. It uses a custom device state within Asterisk switched by an external application. The external application in this case is a bash…
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Setting up shared voicemail on Asterisk – part 1
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It’s a requirement that people often seem to ask for – a single voicemail box, taking messages for a department, that can be easily monitored and accessed by several different users. A typical application would be to record out-of-hours messages which are then checked in the morning by any of a number of users, perhaps just depending who arrives first at the office. While it is fairly easy to configure Asterisk or Trixbox to record the messages, it is less…
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Using Custom Device States to control BLF lamps
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Do you want to know how to use a custom device state to control the lamp on a programmable key of an IP phone? In this article I explain how to set up the hints and make any number of IP phones subscribe to a custom device state and how to switch the custom status from within the Asterisk dial plan. In later articles I plan to show how this can be put to a practical use. I will explain how to…
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How secure is your Asterisk PBX? – part 3
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Getting more advanced In part 2, we looked at several ways in which an Asterisk system administrator can help to make their system more secure, with special emphasis on avoidance of toll fraud. In this, the third and final article in the series, I will pick up on a topic that was left unfinished at the end of part 2 – sip domains. I also want to look at a couple of other topics that were barely touched…
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How secure is your Asterisk PBX? – part 2
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Protecting your Asterisk server In part 1, we examined the techniques that are used to probe for vulnerabilities in a SIP server and reviewed the types of exploitation a would-be hacker hopes to use. In this second part, I look at the ways you can protect your Asterisk or other SIP server and guard against weaknesses that could potentially cost your organisation a lot of money. This article was written before the pjsip channel driver was available,…
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How secure is your Asterisk PBX? – part 1
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A growing problem Like a slice of Victoria sponge cake on a summers day attracts wasps, so new technologies seem to attract the attention of cyber-criminals. The more widely used the technology, the greater the interest. It was inevitable, and widely predicted, that VoIP would become a favorite target for hackers as its popularity and uptake increased – it has the accessibility of an email server combined with the potential for fraud of an online bank account. Irresistible! And so…
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Asterisk behind NAT
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Scenarios in which NAT may adversely affect Asterisk SIP connections The Asterisk Server is behind NAT The Asterisk server could be on the LAN (or in a DMZ) with a NAT firewall between it and the Internet. When it communicates with external peers or devices, the network connections have to pass through the local NAT device. The remote device that is connecting to Asterisk is behind NAT Suppose that your Asterisk server is connected directly to…
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Using SIP Devices behind NAT
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SIP Devices behind NAT: What solutions are available? When an IP phone is installed behind NAT, problems can be created by the NAT device itself, by the phone’s inability to correctly understand its own networking environment or from a combination of the two. Because it is such a common problem, most IP Phones have built-in facilities designed to help them analyse their own networking environment and to help overcome the problems of NAT traversal. Probably the…
