Work it out.
Calculators
Subnet calculator (IPv4)
IPv4 / CIDR notation
Transfer time
Bandwidth
RAID capacity and fault tolerance
RAID-lagerteknologi (branchestandard, jf. SNIA Common RAID Disk Data Format)
UPS battery time (runtime)
Grundlæggende UPS-runtime-fysik (branchepraksis, jf. APC/Eaton runtime-kalkulatorer)
PoE power budget for switch
IEEE 802.3af/at/bt (Power over Ethernet-standarder)
Copper cabling — margin to the 100 m channel limit
TIA/EIA-568 kabling-standard (100 m maks. kanallængde for kobber-Ethernet)
Fibre-optic loss budget (dB)
ITU-T G.652 (fiberdæmpning) + TIA-568.3-D (typiske konnektor-/splejsningstab)
Wi-Fi — realistic throughput
Branchepraksis for 802.11-protokoloverhead (Cisco/Ubiquiti trådløs designvejledning: typisk 50-60% af PHY-raten)
VoIP bandwidth per simultaneous call
Ciscos VoIP-båndbreddetabel, Doc ID 7934 (codec-payload + IP/UDP/RTP-overhead, 20 ms-pakketisering)
Delay budget for voice/video (ITU-T G.114)
ITU-T G.114 (anbefalet maks. 150 ms ende-til-ende-forsinkelse, ≤400 ms accepteret grænse)
Backup storage requirement (3-2-1 rule)
3-2-1-backupreglen (CISA/US-CERT-anbefaling: mindst 3 kopier af data, på 2 forskellige medietyper, 1 kopi offsite)
Helpdesk/service desk capacity
Grundlæggende kapacitetsberegning (ITIL 4 Service Desk-praksis: tilgængelig tid ÷ gennemsnitlig håndteringstid)
Subnetting: number of subnets when borrowing bits
RFC 4632 (CIDR — Classless Inter-Domain Routing, IETF)
Disk capacity — GB (manufacturer) vs. GiB (operating system)
IEC 60027-2 / IEC 80000-13 (binære præfikser: GiB = 2³⁰ bytes, mod decimale SI-præfikser: GB = 10⁹ bytes)
Switch — uplink oversubscription ratio
Cisco campus-netværksdesign — oversubscription højst ca. 20:1 fra adgangslaget og ca. 4:1 fra distributionslaget
Memory usage for a data structure
IEEE 754 (flydende decimal-standard) + almindelige programmeringssprogs heltalsstørrelser
SIEM: log store based on events per second
Log management sizing (EPS × byte × time) · competence objective on SIEM and log management
Quantitative risk assessment (SLE, ARO, ALE)
Quantitative risk analysis: SLE = value × EF, ALE = SLE × ARO (ISC² CISSP CBK; risk = likelihood × consequence, NIST SP 800-30)
Availability from MTBF and MTTR, with redundancy
Availability A = MTBF ÷ (MTBF + MTTR) · parallel redundancy 1 − (1 − A)ⁿ (ITIL Availability Management, IEC 60050-192)
Server room: heat load, cooling and electricity per year
Energy balance: 1 W = 3.412 BTU/h · PUE = total power ÷ IT power (The Green Grid)
Bent bracket
Exact flat pattern
Edge-bent panel
Exact flat pattern
Cable tray
Exact flat pattern
Tools that work in all subjects
Whatever your programme is called, these tools calculate the same — Pythagoras, area, percentages and units are not tied to one trade.
- Pythagorasa² + b² = c²Find the missing side, set out a right angle, check whether a room is square, and find the space diagonal.
- Area and perimeterm²Rectangle, triangle, trapezium, circle and composite shapes — area and perimeter.
- Volume and surface aream³ · lBox, cylinder, cone, sphere, pyramid, prism, pipe and frustum — also in litres.
- Percent%Percentage of, how many per cent, percentage change, discount and VAT.
- Scale and ratios1 : 50From drawing to reality, area and volume to scale, the rule of three and dividing in a ratio.
- Unit convertermm ↔ mFrom mm to km, Pa to bar and kB to GB — with the unit staircase.
- Time calculations and the clockt : minTime between two clock times, add time, and 1.75 h = 1 h 45 min for the timesheet.
- Slope and fall% · ° · 1:xFall from level to level, in per cent, per mille, degrees and mm per metre — and the height difference.
- Material consumption including wastem² + %Boards, paint, battens at c/c spacing and packs — for a composite surface or a whole room, with waste.