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VoIP Over The VPN
Thursday, May 01, 2008
Chances are, if you work for a large corporation, and you do any kind of work from home, you have to have some kind of access to the office remotely. This typically happens through the help of something called a VPN, or virtual private network. Through encryption and strong authentication, and some software magic, your remote PC becomes part of the corporate network.
First of all, there's usually some piece of client software that must be loaded on your system. The exact software will vary depending on the vendor that provides the VPN solution. Despite the fact that most VPNs these days employ either IPSec or SSL--both well known, well-understood standards, the client software is specific to each vendor's implementation.
One challenge that VPNs must deal with is the fact that most clients are behind an address translation device of some sort. The clients are assigned an address by their local router that are not only not reachable from the greater Internet, but may be the same or similar to an IP address on the corporate network.
To resolve this issue, VPN clients create the equivalent of a new networking adapter. This adapter, like your Ethernet or WiFi adapter, are assigned an IP address through the VPN. This IP address is unique within the corporate network and makes each client connected appear as if they are somewhere on the corporate network.
It should, therefore, be possible to use a voice over IP client over a VPN. It's true, it does work, but there are some challenges to make this work acceptably. The main problem is that you're now adding the overhead of encryption. A VPN, as part of the encryption process, must also add a certain amount of data to each packet to ensure the confidentiality and integrity of the data.
Essentially, a VPN adds more overhead into a process where anything over 300 millisecond round-trip times might be a noticeable difference in the quality of the audio. More data that has to be processed more to get where it needs to go will for sure slow things down, but under the right conditions, it can be just like you're in the office.
