How to calculate total budget of QSFP/SFP

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:

Switch port must match.

② Wavelength

Very important to avoid mismatch.

If wavelength mismatches → NO LINK.

③ Distance Support (km)

Buy correct distance based on your link length:

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.