Enterprise telephony platforms (Avaya, Nortel, Cisco Call Manager, Unity)

VoIP protocols & troubleshooting (SIP, RTP, SRTP, H.323, packet analysis)

Network engineering for voice (QoS, VLANs, WAN, latency/jitter management)

Microsoft Teams Phone & cloud voice integration (Direct Routing, Operator Connect)

Session Border Controllers (Ribbon, AudioCodes, SIP normalization)

Telephony migrations & modernization (...