NPS benefits for a retiree

I am a retired  person from a public sector Bank. I am receiving pension from my ex-employer. My queries are as follows.

1. Can I join NPS and avail tax benefits as per 80ccd1?

2. If so, is it necessary to invest in 80ccd1 - tier 1? Can I avail the benefits which are available under 80ccd1b?

May be the reply to this query benefits other pensioners..

Thanks