Do I need a licence to use DVTS ?

NO, DVTS is a free software

DVTS is created to promote high speed realtime Internet communications.
Bandwidth available over the Internet is increasing. However, there are not so many software that promotes high quality communication, and is free to anyone. We think that being a free software is very important. Being used by many people will be the best feedback. Thus, it is a totally free software.

Use of DVTS is free.
You can modify the software as you like.
It would be appreciated if you mention it is a product of WIDE Project, when you use DVTS.
DVTS is written by Akimichi OGAWA (Keio university, JAPAN)
DVTS and FreeBSD firewire patch are individual softwares.
FreeBSD firewire patch is written by Dr. Katsushi KOBAYASHI (CRL).