Gather information from the existing network
Domain 1: Gather information from the existing network
This domain asks you to prove you can discover the current network, the physical environment, and the business requirements before designing anything. The exam favors candidates who can turn raw discovery data into design constraints, not candidates who jump to an AP count.
What discovery must capture
- Existing infrastructure: controller models and code, AP models and counts, license entitlements, switch port speed and PoE budget, VLAN/subnet layout, DHCP and DNS servers, WAN/LAN bottlenecks, and any existing RF survey data.
- Physical environment: floor plans, ceiling height and material, wall/floor attenuation, elevator shafts, metal racks, and interference sources such as microwave ovens, radar, DECT, and LTE.
- Requirements: coverage and capacity targets, client mix (laptops, voice handsets, scanners, IoT), density per area, roaming needs, application SLAs, and security/compliance drivers.
Turning data into constraints
Attenuation values drive AP count: drywall is low loss, concrete and brick are moderate, and metal or rebar concrete is high loss. Capacity is usually the real driver: an AP that covers a conference room may not serve 60 active clients. For voice, design to roughly -67 dBm RSSI, 20 dB SNR, less than 150 ms latency, less than 30 ms jitter, and less than 1% loss. For data, use a realistic per-client throughput and a realistic per-AP aggregate, not the PHY rate printed on the data sheet.
Worked example
A 6,000-seat campus has 120 older APs and 5,500 users, with 2,500 devices active at peak. The customer wants 2 Mbps per active device and no more than 25 active devices per AP. Capacity gives 2,500 / 25 = 100 APs; coverage from the existing plan suggests 140 APs. The design must use the larger number, 140, but also check PoE: if each new AP draws 30 W, 140 x 30 W = 4,200 W, and a 48-port 740 W switch can power only 24 such APs, so at least six access switches are needed. The reasoning is to let the binding constraint, capacity or power, set the count, not the old AP count.
Traps that cost marks
- Treating nameplate AP rates as usable throughput.
- Forgetting that voice and data have different RSSI and SNR targets.
- Missing PoE class and switch power budget changes.
- Ignoring DHCP scope growth and DNS/DHCP relay placement.
- Assuming the existing controller or license count can absorb the new APs.