23 years in telephony. Key systems, PBX's, Central Office engineer, etc...I'm fluent in almost all areas of telecommunications including but not limited to SS7, TDM, IP, VoIP (SIP, MGCP, H.248), FoIP (g.711 fallback and T.38), ISDN (q.921, q.931), transport networks including layer 2, SONET, GigE, etc...