S
- SBC (Session Border Controller)
- Scalability
- SDP (Session Description Protocol)
- Seamless Handoff
- Secondary Rate Interface (SRI)
- Secure Real-Time Transport Protocol (SRTP)
- Secure RTP (SRTP)
- Secure Shell (SSH)
- Security
- Server
- Server Redundancy
- Service Assurance
- Service Discovery
- Service Provider
- Session Border Controller (SBC)
- Session Initiation Protocol for Instant Messaging and Presence Leveraging Extensions (SIMPLE)
- Session Manager
- Shared Line Appearance
- Signaling
- Signaling System No. 7 (SS7)
- Single Number Reach (SNR)
- SIP (Session Initiation Protocol)
- SIP ALG (Application Layer Gateway)
- SIP Forking
- SIP Gateway
- SIP INFO
- SIP Notify
- SIP OPTIONS
- SIP Phone
- SIP Proxy
- SIP Proxy Server
- SIP Redirect Server
- SIP Registration
- SIP Session Timer
- SIP Trunk
- SIP Trunking
- SIP URI (Uniform Resource Identifier)
- SLA (Service Level Agreement)
- SLA Monitoring
- SMDR (Station Message Detail Recording)
- SMS (Short Message Service)
- Soft Key
- Softphone
- Softswitch
- Software as a Service (SaaS)
- Software Maintenance
- Software Update
- Software-Defined Networking (SDN)
- Speech Codec
- Speech Recognition
- SRTP (Secure Real-Time Transport Protocol)
- SSID (Service Set Identifier)
- SSL (Secure Sockets Layer)
- STUN (Session Traversal Utilities for NAT)
- Subscriber
- Subscriber Line Interface Circuit (SLIC)
- Subscriber Loop
- Supervisory Signal
- Switch
- Switching Fabric
- Synchronous Optical Networking (SONET)
- System Administrator
- System Integration
