Switch classes & form factors: fixed, modular, stackable, industrial, white-box

The same forwarding ASIC ships in a 1U pizza box, a stackable campus switch, a 16-slot chassis line card and a DIN-rail industrial unit. The packaging decides how many optics the box carries, how it is powered and cooled, whether the air flows from the port side or toward it, how modules are replaced and what the vendor's policy toward them looks like. This page classifies switches by form factor and market, lists the parts of a chassis system, and explains airflow, redundancy and environmental limits from the transceiver's point of view.

Classes by market and management

Class	Management	Ports	Optics policy	Examples of use
Unmanaged	none	5–24 RJ45, 1–2 SFP	accepts anything that links; no DDM visible	desktop, small office
Smart / web-managed	web UI, limited CLI	8–48 RJ45, 2–4 SFP/SFP+	permissive; DDM sometimes shown	SMB, edge
Managed enterprise (campus)	full CLI/API, stacking	24–48 access + 2–8 uplinks	vendor-dependent, often strict (How each NOS validates a module)	offices, campus
Data-centre fixed	CLI/API, automation	32–64 × 100G–800G	often permissive on merchant silicon	leaf, spine
Data-centre chassis	CLI/API, redundant supervisors	hundreds of ports on line cards	vendor-dependent	core, large spine
Carrier / aggregation router with optics	full	mixed 1G–400G, coherent	strict, OEM lists	metro, mobile backhaul
Industrial	CLI/web, ring protocols	8–28, DIN-rail, −40…+75 °C	permissive; industrial-grade optics needed (Temperature grades)	plants, rail, energy
White-box / disaggregated	SONiC, Cumulus, other open NOS	as DC fixed	platform plugin, permissive (NOS landscape)	hyperscale, cloud
Blade / embedded	via chassis manager	internal midplane + uplinks	vendor	blade servers
PON OLT (a switch in disguise)	full	PON SFP/XFP ports + uplinks	strict on PON optics classes	access operators

Form factors

Form factor	Height	Ports	Power	Notes
Fixed 1U (pizza box)	1U	24–64	1–2 PSUs, 150–2 000 W	most switches; fans in a row at the back
Fixed 2U	2U	64–128 or deep-buffer/high-power (400G/800G, coherent)	2–4 PSUs	800G boxes and ZR-heavy platforms
Stackable	1U each, up to 8–10 in a stack	48 per unit	per unit	one management plane (Stacking & MLAG)
Modular fixed	1U with uplink/expansion module slots	—	—	uplink modules have their own optics lists
Chassis	4–21U	4–18 line-card slots + 2 supervisors/route processors + fabric cards	N+1 / N+N PSUs, kW-class	line cards replaced hot; optics per card
Industrial DIN-rail	compact, fanless	8–28	12–48 V DC, dual input	conduction-cooled; module heat matters
Ruggedised rack	1U, fanless or filtered	24–28	AC/DC	extended temperature
Blade chassis module	per blade slot	internal + 4–8 uplinks	from chassis	—

Anatomy of a chassis system

Component	Function	Optics relevance
Line card	ports + PHYs + part of forwarding	each card has its own supported-optics list and cage generation; mixing generations in one chassis is normal
Supervisor / route processor / control card	control plane, management	reads every module through the card CPLDs
Fabric card / switch fabric	connects line cards	no optics (some designs use internal optics, CPO in future)
Midplane / orthogonal direct	electrical connection card ↔ fabric	—
Power entry modules, PSUs	N+1 or N+N	a card of 36 × 400G optics adds ~400 W
Fan trays	front-to-back or side-to-side	replaced hot; a failed tray overheats the optics on that row first

Airflow direction and optics

Airflow	Meaning	Where	Consequence for modules
Port-side intake (front-to-back)	cold air enters at the ports, exits at PSUs/fans	data-centre standard, cold aisle at the front	modules sit in the coldest air; best case
Port-side exhaust (back-to-front)	air enters at the rear, exits over the ports	leaf switches mounted with ports toward the hot aisle (rear of the rack) so that server DACs stay short	modules sit in exhaust air 10–20 °C warmer; DDM temperatures run high; choose airflow SKU accordingly
Side-to-side	intake on one side	campus, telecom racks, chassis line cards in some designs	needs side clearance; blocked side panels overheat one end of the card
Reversible fans	fan trays or PSUs ordered as "AFO"/"AFI" (air flow out/in at port side)	many DC platforms	mixing directions in one box is refused by the NOS or overheats it

Rule: match the switch's airflow SKU to the rack's hot/cold aisle and the direction of the servers it connects; check that module heat sinks face the cage's thermal path (Power & consumption, Power & thermal).

Environmental limits of the box itself

Item	Enterprise / DC	Industrial
Operating temperature (ambient)	0…40 °C (some 45)	−40…+75 °C
Storage	−40…+70 °C	−40…+85 °C
Humidity	10–90 % non-condensing	5–95 %
Altitude	up to 3 000 m (derated above 1 800)	—
Acoustic	50–75 dBA at full fan speed	fanless
Vibration/shock	rack standard	IEC 60068, EN 50155 (rail)

A commercial-grade optic in a switch whose ambient hits 40 °C sees a case temperature near its 70 °C limit; industrial switches need industrial optics.

Redundancy

Element	Typical redundancy	What fails if missing
PSU	1+1 (fixed), N+1 / N+N (chassis)	full box on PSU or feed failure
Fans	N+1 in tray	thermal shutdown after minutes
Supervisor	1+1 with stateful switchover (chassis)	control plane; forwarding may continue (NSF)
Uplinks	2+ on different modules/cards, LAG or ECMP	isolation of the whole access block
Stack members	ring topology	split stack on cable failure
Optics	spares on site (5–10 %)	hours of outage for a module worth a coffee

White-box and disaggregation

ODM hardware (Edgecore/Accton, Celestica, UfiSpace, Delta, Wistron, Quanta) runs SONiC, Cumulus/NVUE or a vendor NOS chosen separately. For optics: the platform plugin (not a policy) reads modules, CMIS support depends on the NOS release, and compatibility testing is the operator's job — the reason hyperscalers publish their own qualified-optics lists (Compatibility matrices & firmware).

In CodingBox

The class of switch tells you the policy to expect: campus and carrier gear checks identities, DC and white-box gear mostly parses them, industrial gear needs I-temp modules. CodingBox shows the identity bytes the strict classes check and the thresholds that hint at the module's temperature grade (Check transceiver).