This is what Gen. Martin Dempsey, Chairman of the US Joint Chiefs of Staff, meant when he pointed out that “Syria's air defenses were five times more sophisticated as those in Libya, making airstrikes riskier and more complicated.”
So if the US, any NATO power, Turkey, Saudi Arabia or Qatar, is inclined to embark on military operations to enforce security zones in Syria under a protective umbrella of no fly-zones on the Libyan model, Gen. Dempsey warned them they would be lethally challenged by a dense network of sophisticated Russian-made air defenses operated by Russian experts. This network also shielded the Iranian airlift to Syria from attack.