according to the link below between North and South terminals in Gatwick 140 min is suggested.
[broken link removed]
If you have 1 flight ticket, ie dub-gatwick, and then a gatwick-outer mongolia... all on the 1 ticket, rather than 2 separate tickets, I believe that if you miss the connection the carried must provide you with a seat on the next available flight (at least that was the IATA regulations a few years back). Separate tickets don't have that safety net.