How long should you wait after submitting a revise and resubmit before you should contact the journal? It's been six weeks since I have sent paper for a second review after I received revise&amp;resubmit decision from the first round. Is this a typical time period or should I send a query to the journal? 

Currently the paper is under the status "with editor" for a couple of days after it has been "under review". The journal is in the field of telecommunications.
The time for the second go-around is often the same as for the first go-around. So, if the journal allows reviewers 3 months for a review, you have to expect this much (at least) also for the review of the revision.