Russian military advisers are manning some of Syria's more sophisticated air defences – something that would complicate any future US-led intervention...The advisers have been deployed with new surface-to-air systems and upgrades of old systems, which Moscow has supplied to the Assad regime since the Syrian revolution broke out 21 months ago.

(Later) The upgrades were supplied by Moscow, which sees them as a bulwark against western-imposed regime change and protection of a longstanding investment in Syria. The country includes Russia's biggest electronic eavesdropping post outside its territory, in Latakia, and its toehold on the Mediterranean, a small naval base at Tartus.
Link:http://www.guardian.co.uk/world/2012...nce?CMP=twt_fd

Some interesting points, I'm puzzled that no mention IIRC has been made of the ELINT post before. Given the reported lack of regime manpower aqnd apparent desperation one wonders if the air defence network is fully manned.