I forgot to answer your question about conventions, Alan. As a guide to etiquette on entering a pub where music is in progress, I cant do better than tell you what happened one night in Dingle. I was playing in the Droichead Beag with the Boat Band.It was a bit crowded, and we were set up just inside the door, with Rob the Bones playing standing on a bench with his back to the door. Seamus Begley came in as we were in the middle of a tune, put his hand between Rob's legs and squeezed his bollocks. Rob fell off the bench onto a table and spilled several pints. That is how I would suggest you might try approaching a session in progress, it's a great ice-breaker.