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How to Go Around ISPs Blocking VoIP Ports

Updated on April 12, 2011

ISPs and VoIP Blocking

It's easy to see why VoIP is a technology fraught with danger for many authorities. Whether they're the government or the private sector, it seems that everyone feels that it's simply too dangerous to allow anyone to talk to anyone else for free without restrictions. Corporations can block VoIP either at the behest of governments or to protect their business strategy which includes making users subscribe to their expensive telephone plans. Even hotels which offer Internet services for which the customers pay for can attempt to block VoIP ports so that their own phone services will be used.

Governments of course have a variety of reasons for blocking VoIP. They like to be able to track things and encrypted VoIP is impossible to do so. So the simple solution is to block VoIP in many countries around the world. In this article, we look at the most important way in which this is accomplished and in what situations it is applied. We'll also see some of the ways we can bypass such blocks and the risks that they present.

Blocking VoIP
Blocking VoIP

Bypassing port blocking

In many countries, the companies which provide Internet access are also the ones who provide telephone services. This is because the Internet started off with dial up and they already had the infrastructure in place. Mobile carriers who provide data plans therefore have the ability to restrict VoIP calls on all mobile devices. Hosted mobile VoIP systems suffer greatly though this kind of blocking.

The most common way of blocking VoIP services is by blocking the ports through which they operate. Each VoIP protocol specifies a certain port through which the service is provided. In the case of SIP, this is usually port 5060 or 5061. Since more and more VoIP providers are using SIP as their protocol, it's becoming easy to block this single port and thereby disable most VoIP functionality.

To bypass VoIP blocking, it's necessary to use another port. One way is to ask your VoIP provider whether or not they allow their hosted SIP proxy servers to be accessed through any other port. They might or they might not. If they don't, there's no way to access an SIP service directly.

The other option is to find a "proxy for the proxy" which you can connect to from another port. Though this bypasses the port blocking, it's dangerous since you have to absolutely trust the server through which you're connecting to the original SIP proxy.

These are two of the most important ways by which we can bypass VoIP port blocking by ISPs.


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