What is “Total Budget” in SFP/QSFP?
Total Optical Budget (Link Budget) =
Transmitter Power (Tx) – Receiver Sensitivity (Rx)
This tells how far the SFP/QSFP can work, based on fiber losses.
Example:
Tx = +3 dBm
Rx = –25 dBm
Optical Budget = 3 – (–25) = 28 dB → ~40 km support.
What You MUST KNOW Before Buying SFP/QSFP
These are the 9 MOST IMPORTANT points to check:
① Protocol / Data Rate
You must check speed compatibility:
|
Type |
Speed |
Examples |
|
SFP |
1.25G |
1310nm 10km, 1550nm 40km |
|
SFP+ |
10G |
SR, LR, ER, ZR |
|
QSFP+ |
40G |
SR4, LR4 |
|
QSFP28 |
100G |
SR4, LR4, ER4, BIDI, ZR4 |
|
QSFP56 |
200G |
FR4, SR4 |
|
QSFP-DD |
400G |
DR4, FR4, LR4 |
Switch port must match.
② Wavelength
Very important to avoid mismatch.
|
Range |
Typical Wavelength |
|
Short distance |
850nm (MM) |
|
Medium distance |
1310nm |
|
Long distance |
1550nm |
|
BIDI |
1270/1330 or 1490/1550 |
If wavelength mismatches → NO LINK.
③ Distance Support (km)
Buy correct distance based on your link length:
|
Type |
Distance |
|
SR |
100m |
|
LR |
10 km |
|
ER |
40 km |
|
ZR |
80 km |
|
ZR4 / DCO |
120 km – 1000+ km |
Compatibility with Brand (Coding)
Very important for Cisco, Huawei, Juniper, Nokia.
You must check:
- Coding: Cisco / Huawei / Juniper / Mikrotik / DELL / HP
- Locked or open?
- DOM supported?
For D-TECH you sell multi-vendor coding → best for Nepal.
Single Fiber (BIDI) or Dual Fiber
Choose correct type:
- Dual fiber = TX & RX separate fibers
- Single fiber (BIDI) = save cost, used in ISP/FTTH backhaul
Temperature
- Standard: 0°C to 70°C
- Industrial: –40°C to +85°C
Hydropower, Tower, Outdoor → Industrial grade required.
Brand, Warranty, Quality
Always check:
- Vendor reliability
- Laser type (FP / DFB / EML)
- Chipset brand (MACOM, Broadcom, Hisense, OE Solutions, Source Photonics, etc.)
- Warranty (1–3 Years)
- Test report (DDM/DOM)
3. TOTAL BUDGET CALCULATION (DETAILED EXAMPLE)
Given:
- Distance = 25 km
- Fiber @1550nm = 0.22 dB/km ( Nepal’s Loss 0.55db/km)
- Connectors = 2 × 0.3 = 0.6 dB ( Splicer loss can be 0.8db)
- Splices = 20 × 0.05 = 1 dB ( Splicer loss can be 0.1db)
Depends on quality of goods .
Loss Calculation
Fiber loss = 25 × 0.22 = 5.5 dB
Total loss = 5.5 + 0.6 + 1 = 7.1 dB
SFP DATA
10G SFP+ 40 km:
- Tx: +3 dBm
- Rx: –23 dBm
Optical Budget = 26 dB
Conclusion
Your total loss = 7.1 dB
Supported = YES (Below 26 dB budget)
SFP will work perfectly.