Tag: voip
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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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VoIP QoS Settings – part 2
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In part 1, we examined the Layer 2 QoS settings available on most VoIP equipment. In this second part, I will explore the Layer 3 parameters and offer practical suggestions for the values that should be assigned to them. We will briefly look at the history and structure of the ToS and DSCP fields and their place within the DiffServ packet prioritisation model. Recap I explained in part 1 how Layer 2 data can be tagged…
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VoIP QoS Settings – part 1
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The QoS settings on VoIP phones and related equipment can be perplexing. Here, I will attempt to explain what parameters like CoS, ToS, DiffServ and DSCP really mean and offer practical suggestions for the values that should be assigned to them. Part 1 of this article starts with a broad overview and then focuses on Layer 2 network QoS settings; i.e. the settings associated with the VLAN tag in 802.1 Ethernet protocols. If you are looking…
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Installing Mediaproxy 2 on CentOS 5 64bit
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Mediaproxy 2 is a Python application from AG-Projects which is available as a free download as well as being available as a commercial product from AG-Projects. It is used in combination with the Mediaproxy module of OpenSIPS. Unlike Mediaproxy 1, the new version has a lot of dependencies and it can be quite tricky to install. The INSTALL instructions that come with the package are very helpful, but unfortunately they are aimed primarily at installers who…
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Installing OpenSIPS v1.6.1 on CentOS 5 64bit
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Smartvox Limited offered consultancy for installation and configuration of OpenSIPS, Asterisk and PSTN gateways. If you want to do it all yourself, here is a set of instructions that should help. Installing OpenSIPS v1.6.1 on CentOS 5 64 bit is very straightforward. All the dependencies can be installed using YUM. The packages required will depend on the modules that you intend to use from OpenSIPS. This page describes what must be installed to use OpenSIPS with…
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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…
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SIP and NAT: Why is it a problem?
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Why is it a problem using SIP Clients behind NAT? What is NAT? To understand why SIP Clients behind NAT are a problem, you need to first have some understanding of what NAT is and what it does. NAT stands for Network Address Translation. Unless you are using One-to-one NAT, then a NAT device may also perform Port Address Translation (PAT). For a detailed explanation of NAT click here. If you want, you can also read…
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SIP Registration Explained
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How does SIP Registration work and why is it needed? Registration – what it is and why it is necessary IP Phones (and SIP clients in general) need to register with a central server mainly because this allows the phone’s location to be known when it is required to receive an incoming call. The “location” is identified by an IP address and port number. In some cases the IP address might be permanent and fixed, in…
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SIP Servers Explained
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What are SIP Servers and why are there so many? SIP and SIP Servers – a brief explanation SIP is a general purpose Session Initiation Protocol that can be used as the basis for a range of services that extend beyond VoIP to video, Presence and beyond. It is a powerful and highly versatile protocol that can be used for signalling and to establish and terminate communication sessions between end-points. Even within the voice environment, SIP…
