Abbreviations A–Z

Optics documentation is written in acronyms: a datasheet line reads "SFP28 SR, 850 nm VCSEL, RS-FEC, OMA −6 dBm, DDM per SFF-8472". This index expands the abbreviations you meet in datasheets, switch output and CodingBox screens, with one line of meaning and a link to the material that explains the concept. For definitions of concepts rather than expansions see the Glossary.

A–B

Abbr.	Expansion	Meaning
A0h / A2h	two-wire addresses 0xA0 / 0xA2	identity and diagnostics memory of SFP-class modules (Memory map)
AEC	Active Electrical Cable	copper cable with retimers/DSP in the plugs (Cable internals)
ACC	Active Copper Cable	copper cable with linear amplifiers, no retiming
AN	Auto-Negotiation	speed/FEC negotiation, IEEE 802.3 Clause 73 on DAC (FEC & AN)
AOC	Active Optical Cable	fibre cable with fixed transceivers at both ends
APC	Angled Physical Contact	8° angled connector polish, green (Connectors)
APD	Avalanche Photodiode	high-sensitivity receiver for long reach (Receivers)
ASE	Amplified Spontaneous Emission	noise generated by optical amplifiers (OSNR)
ASIC	Application-Specific Integrated Circuit	the switch forwarding chip (Inside a switch)
AUI	Attachment Unit Interface	chip-to-module electrical interface: XAUI, CAUI-4, 400GAUI-8…
AWG	Arrayed Waveguide Grating / American Wire Gauge	DWDM mux technology / copper conductor gauge in DAC
BASE-R / BASE-X	—	IEEE PCS families: 64b/66b (R) and 8b/10b (X)
BER	Bit Error Ratio	errored bits ÷ transmitted bits (Units)
BiDi	Bidirectional	one-fibre link with two wavelengths (Wavelength bands)
BOSA	Bidirectional Optical Sub-Assembly	TOSA + ROSA + filter in one package

C–D

Abbr.	Expansion	Meaning
CAUI	100 Gb/s AUI	CAUI-10 (10 × 10G), CAUI-4 (4 × 25G)
CC_BASE / CC_EXT / CC_DMI	checksums	EEPROM checksums per SFF-8472/8636 (Checksums)
CDB	Command Data Block	CMIS command mechanism (firmware upgrade etc.) (CMIS)
CDR	Clock and Data Recovery	retiming circuit (CDR)
CEI	Common Electrical I/O	OIF electrical interface specs (CEI-28G, -56G, -112G)
CFP	C Form-factor Pluggable	100G/coherent module family
CMIS	Common Management Interface Specification	management for QSFP-DD, OSFP and others
COB	Chip-on-Board	die-on-PCB packaging (COB)
CPO	Co-Packaged Optics	optics integrated with the switch ASIC
CPRI / eCPRI	Common Public Radio Interface	mobile fronthaul protocols (Fronthaul)
CR / CR4 / CR8	copper	IEEE PMD names for DAC (25GBASE-CR, 100GBASE-CR4)
CRC	Cyclic Redundancy Check	frame check; CRC errors = link errors
CWDM	Coarse WDM	20 nm grid, 18 channels (CWDM)
DAC	Direct Attach Cable	passive twinax copper cable
DCM	Dispersion Compensation Module	fibre spool or grating compensating chromatic dispersion
DDM / DOM	Digital Diagnostics Monitoring / Digital Optical Monitoring	live temperature, voltage, bias, powers (DDM basics)
DFB	Distributed Feedback laser	single-mode laser for 1310/1550 nm (Lasers)
DML	Directly Modulated Laser	laser whose current is modulated
DP	Data Path	CMIS lane group with its state machine
DR / DR4 / DR8	500 m PMD	single-mode parallel 500 m PMDs
DSP	Digital Signal Processor	PAM4 and coherent signal processing (DSP)
DWDM	Dense WDM	100/50 GHz grid (DWDM)

E–G

Abbr.	Expansion	Meaning
EDFA	Erbium-Doped Fibre Amplifier	C/L-band optical amplifier
EEPROM	Electrically Erasable Programmable ROM	module memory
EML	Externally Modulated Laser	DFB + electro-absorption modulator
EPON / GPON / XGS-PON	Ethernet / Gigabit / 10G-symmetric PON	PON generations (PON standards)
ER / ER4 / ER8	Extended Reach	40 km PMDs
ER (optical)	Extinction Ratio	P1/P0 of the transmitter, dB
ESD	Electrostatic Discharge	handling hazard for modules
FC / GFC	Fibre Channel / Gigabit FC	storage network (Fibre Channel)
FEC	Forward Error Correction	BASE-R (Fire code), RS-FEC (528/544)
FP	Fabry-Pérot laser	multi-mode laser for short SMF links
FR / FR4 / FR8	2 km PMD	single-mode 2 km PMDs
FTTx	Fibre To The x	home/building/curb access
GBIC	Gigabit Interface Converter	first-generation 1G module (GBIC)
GAUI	e.g. 400GAUI-8	AUI at 400G with 8 lanes
GBd	gigabaud	symbols per second (Units)

H–L

Abbr.	Expansion	Meaning
HA / HW / LA / LW	High Alarm / High Warning / Low Alarm / Low Warning	DDM thresholds (Thresholds)
HBA	Host Bus Adapter	FC server adapter
HDR / NDR / XDR	InfiniBand generations	200 / 400 / 800 Gb/s (InfiniBand speeds)
I²C / TWI	Inter-Integrated Circuit / Two-Wire Interface	the management bus (Two-wire interface)
IB	InfiniBand	HPC/AI interconnect
IEC	International Electrotechnical Commission	connector, fibre, laser-safety standards (Standards map)
IEEE 802.3	Ethernet working group	PMD, PCS, FEC standards
INF-8077i	XFP MSA document	XFP management (XFP)
ITU-T	International Telecommunication Union, Telecom sector	fibre (G.652), grids (G.694.x), PON (G.984/G.9807), OTN (G.709)
KR / KR4	backplane	IEEE backplane PMDs; KP4 = RS(544,514) FEC
LC	Lucent Connector	the standard duplex connector
LOL	Loss of Lock	CDR cannot lock
LOS	Loss of Signal	receiver sees no light
LPMode / LowPwr	Low Power mode	module held at ≤ 1.5 W (Power & thermal)
LPO	Linear Pluggable Optics	DSP-less module relying on host equalisation
LR / LR4 / LR8	Long Reach	10 km PMDs
LRM	Long Reach Multimode	10GBASE-LRM, 220 m on OM1/OM2
LWDM / LAN-WDM	LAN Wavelength Division Multiplexing	800 GHz grid around 1300 nm used by LR4/ER4
LW / SW / ELW	Long / Short / Extended Long Wave	Fibre Channel optic types

M–O

Abbr.	Expansion	Meaning
MAC	Media Access Control	Ethernet framing layer
MDIO	Management Data I/O	PHY management bus (not used by modules)
MIS	Management Interface Specification	SFP-DD management (MIS)
MMF / SMF	Multi-Mode / Single-Mode Fibre	50/62.5 µm core vs 9 µm
ModPrsL / MOD_ABS	Module Present (active low) / Module Absent	presence pin
MPO / MTP	Multi-fibre Push-On / MTP® brand	12/16/24-fibre connector
MSA	Multi-Source Agreement	industry agreement for a form factor (MSA overview)
MTBF	Mean Time Between Failures	reliability figure, hours
MZM	Mach-Zehnder Modulator	external modulator (silicon photonics, coherent)
NIC	Network Interface Card	server adapter
NOS	Network Operating System	switch software (NOS landscape)
NRZ	Non-Return-to-Zero	two-level modulation
NVMe-oF	NVMe over Fabrics	storage protocol (NVMe-oF)
OADM / ROADM	(Reconfigurable) Optical Add-Drop Multiplexer	WDM node
OIF	Optical Internetworking Forum	CEI, 400ZR, CMIS 5.x
OLT / ONU / ONT	Optical Line / Network Terminal / Unit	PON head-end and subscriber ends
OM1–OM5 / OS1–OS2	Optical Multimode / Singlemode grades	ISO/IEC 11801 fibre classes
OMA	Optical Modulation Amplitude	P1 − P0, the modulated power
OSFP	Octal SFP	8-lane form factor (OSFP)
OSNR	Optical Signal-to-Noise Ratio	dB in 0.1 nm, DWDM quality figure
OTDR	Optical Time-Domain Reflectometer	fibre fault locator
OTN	Optical Transport Network	ITU-T G.709 framing
OUI	Organizationally Unique Identifier	IEEE vendor ID in EEPROM (Vendor fields)

P–R

Abbr.	Expansion	Meaning
PAM4	4-level Pulse Amplitude Modulation	2 bits per symbol
PCS / PMA / PMD	Physical Coding / Medium Attachment / Medium Dependent sublayers	IEEE physical layer stack
PFC / ECN	Priority Flow Control / Explicit Congestion Notification	lossless Ethernet (Lossless Ethernet)
PIC	Photonic Integrated Circuit	integrated optics chip
PIN	p-i-n photodiode	standard receiver
PLL	Phase-Locked Loop	clock circuit
PN / SN	Part Number / Serial Number	identity fields (Part numbering)
PON	Passive Optical Network	shared-fibre access network
PRBS	Pseudo-Random Binary Sequence	test pattern (PRBS31, PRBS13Q)
PSM4	Parallel Single Mode 4-lane	100G 500 m MSA
QSA	QSFP-to-SFP Adapter	run an SFP module in a QSFP port (Port types)
QSFP / QSFP-DD	Quad SFP / Double Density	4- and 8-lane form factors
RDMA / RoCE	Remote Direct Memory Access / RDMA over Converged Ethernet	AI/storage transport
RIN	Relative Intensity Noise	laser noise figure
RMA	Return Merchandise Authorization	warranty return
RoHS	Restriction of Hazardous Substances	EU directive, label marking
ROSA / TOSA	Receiver / Transmitter Optical Sub-Assembly	optical front end (Components)
RS / RS0 / RS1	Rate Select	pins/bits selecting rate (Rate select)
RS-FEC	Reed-Solomon FEC	RS(528,514) Clause 91/108, RS(544,514) KP4
Rx / Tx	Receive / Transmit	—
RX_LOS	receiver loss of signal pin	hardware LOS output

S

Abbr.	Expansion	Meaning
SAN	Storage Area Network	FC or Ethernet storage fabric
SC	Subscriber Connector	2.5 mm push-pull connector
SerDes	Serializer/Deserializer	high-speed lane transceiver in ASICs
SFF / SNIA	Small Form Factor committee / Storage Networking Industry Association	publishers of SFF-8xxx
SFI / SFI+	SFP+ high-speed serial interface	electrical interface of SFP+ (SFF-8431)
SFP / SFP+ / SFP28 / SFP56 / SFP-DD	Small Form-factor Pluggable family	1 / 10 / 25 / 50 / 100 Gb/s (Form factors)
SGMII	Serial Gigabit Media Independent Interface	1G copper SFP electrical mode
SiPh	Silicon Photonics	CMOS-made optics
SMSR	Side-Mode Suppression Ratio	single-mode laser purity, dB
SNMP	Simple Network Management Protocol	monitoring (Monitoring)
SNR	Signal-to-Noise Ratio	—
SOA	Semiconductor Optical Amplifier	on-chip preamplifier
SONiC	Software for Open Networking in the Cloud	open NOS
SR / SR4 / SR8	Short Reach	850 nm multi-mode PMDs
SWDM	Short Wavelength Division Multiplexing	4 wavelengths 850–940 nm on OM5

T–Z

Abbr.	Expansion	Meaning
TDECQ	Transmitter and Dispersion Eye Closure Quaternary	PAM4 transmitter quality, dB
TDP	Transmitter Dispersion Penalty	NRZ transmitter penalty, dB
TEC	Thermo-Electric Cooler	Peltier element stabilising laser temperature
TIA	Trans-Impedance Amplifier / Telecommunications Industry Association	receiver amplifier / standards body (TIA-568)
TX_DISABLE / TX_FAULT	transmitter disable / fault pins	hardware control and status (SFP hardware)
UI	Unit Interval	one symbol period
UPC	Ultra Physical Contact	flat polish, blue connectors
USR	Ultra Short Reach	vendor 850 nm PMD, ~100 m on OM3
VCSEL	Vertical-Cavity Surface-Emitting Laser	850 nm multi-mode laser
VDM	Versatile Diagnostics Monitoring	CMIS advanced diagnostics (VDM)
VOA	Variable Optical Attenuator	adjustable attenuator
VRP / EOS / NX-OS / Junos	vendor NOS names	Huawei / Arista / Cisco / Juniper
WDM	Wavelength Division Multiplexing	many wavelengths on one fibre
XAUI / XGMII	10 Gigabit AUI / Media Independent Interface	10G chip interfaces
XFP	10 Gigabit Small Form-factor Pluggable	legacy 10G module (XFP)
XG-PON / XGS-PON	10-Gigabit (Symmetric) PON	ITU-T G.987 / G.9807
XLAUI	40 Gb/s AUI	4 × 10G
ZR / ZR+	—	80 km PMD; coherent 400ZR/OpenZR+ (Coherent)

In CodingBox

Most of these abbreviations appear verbatim on the Check screen — compliance codes, DDM flags, CMIS states, power classes. The glossary explains the concepts; this page decodes the letters.