H1B 6 year limit: is physically absent from USA necessary?

If you have H1B for 6 years and the green card process hasn't started or reached a certain stage (filing of PERM), ir order to get a new H1B, are you required to be physically absent from USA for 1 year or can you switch to other visa (such as TN or student/H4 visa) for 1 year?


My current H1B starts Sep. 2004 and will expire Sep. 2010. My current job is in danger. Very few companies are willing to do H1B transfer given that I only have 1.5 year left on H1B, and many companies can't start green card within 6 months or so because they are laying off people. I am thinking about finding a job using TN visa (I am a Canadian citizen).

If I use TN now, and switch to H1B after Sep. 2010, I guess that I can still have 1.5 year left on my H1B, and my H1B application will not be subject to the quota. Right? 1.5 year after got my new H1B (H1B total time will be 6 year by then), I may run into the issue as above.

Thanks a lot.