Technology and Infrastructure
What this domain tests
Technology and Infrastructure covers the physical and virtual plumbing of a voice platform: signaling and media protocols, codecs, network paths, endpoint hardware, and the virtualization or cloud layer beneath them. Candidates should be fluent in the split between signaling (SIP, which negotiates sessions) and media (RTP, which carries audio), and understand why they travel different paths and fail differently. Know the roles of codecs such as G.711, G.722, and Opus, and the trade-off between bandwidth and voice quality. Grasp NAT traversal, since most real calls cross address translation and media can silently fail while signaling succeeds.
Traps to watch
Questions often hide a fault in the layer the stem does not mention. A "no audio on connect" symptom with successful signaling points to media, firewall, or NAT, not to dial-plan logic. Another trap is conflating one-way and two-way audio, which have different root causes. Watch for units: bandwidth per call versus per concurrent call, and codec bitrate versus packet rate. A frequent distractor is treating quality-of-service marking as a fix for insufficient bandwidth; it prioritizes, it does not create capacity.
Worked rule of thumb
Estimate bandwidth by multiplying per-call payload by concurrent calls, then add transport and protocol overhead of roughly 20 to 30 percent. For example, G.711 at about 64 kbps payload across 50 concurrent calls is roughly 3.2 Mbps of payload; with overhead, plan for about 4 Mbps of dedicated capacity before any video. If the stem gives you concurrent calls and a codec, do the arithmetic before choosing an answer.
Study focus
Prioritize protocol roles, codec properties, NAT and firewall behavior, and capacity math.