Skype Dropout

I use Skype to contact people outside my office building on landlines and to talk to other people in the office building and around the world. I can hear them perfectly clearly but my signal - my voice comes and goes for them. It's like the signal drops out every so often.

If I was to count to 30 every 6 seconds they would miss 3 seconds or 3 numbers I was speaking.

Is this a problem created by our LAN or is it a PC issue (my brand new dell laptop) or are there other possibilities.

Many thanks
Bruce

PS. I have the latest Skype upgrade with Beta video as we use video too.