To my opinion European Security system does not exist at present. There may be various EU – NATO military arrangements, there may be some other specific and partial arrangements but non of these is truly European nor offering equal security for all European countries.  
OSCE, put aside the name (Organization for Security and Cooperation of Europe), has proved to be futile if not counterproductive in its activities. Even more, in many instances it has been subject to various manipulations favoring positions and partial interest of certain countries. It has played negative role during Yugoslav crises abandoning Final Helsinki Document principles on sovereignty, territorial integrity and inviolability of the internationally recognized state boarders. It has also violated the principle of consensus introducing new “principle” – “consensus minus one”. It’s Mission in Serbian Autonomous Province of Kosovo and Metohija, at the end of 1998. and beginning of 1999, known as Kosovo Verification Mission (KVM), acted rather as an extension and preparatory for 1999 NATO military aggression then as civil diplomatic mission as defined by Yugoslavia – OSCE October 1998 Agreement.
European Security system should be a matter of right and duty of all and each European country and not a monopoly of any regional organization, be it NATO or any other. All European countries should have equal guaranties for their own security. European Security System should be worked out through diplomatic consultations which will take time and efforts and finalized at the European Summit Conference adopting European Security Treaty.