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NFX250 Network Cable and Transceiver Planning

Pluggable Transceivers Supported on NFX250 Devices

Uplink module ports on NFX250 devices support SFP and SFP+ transceivers. This topic describes the optical interfaces supported for those transceivers. It also lists the copper interface supported for the SFP transceivers.

Note:

We recommend that you use only optical transceivers and optical connectors purchased from Juniper Networks with your Juniper Networks device.

CAUTION:

If you face a problem running a Juniper Networks device that uses a third-party optic or cable, the Juniper Networks Technical Assistance Center (JTAC) can help you diagnose the source of the problem. Your JTAC engineer might recommend that you check the third-party optic or cable and potentially replace it with an equivalent Juniper Networks optic or cable that is qualified for the device.

The tables in this topic describe the optical interface support over single-mode fiber-optic (SMF) and multimode fiber-optic (MMF) cables and over the copper interface for SFP transceivers:

  • Table 1—Optical interface support and copper interface support for Gigabit Ethernet SFP transceivers in NFX250 devices.

  • Table 2—Optical interface support for Gigabit Ethernet SFP+ transceivers.

Table 1: Optical Interface Support and Copper Interface Support for Gigabit Ethernet SFP Transceivers in NFX250 Devices

Ethernet Standard

Specification

Value

1000BASE-T

Model number

EX-SFP-1GE-T

Rate

10/100/1000 Mbps

Connector type

RJ-45

Transmitter wavelength

Minimum launch power

Maximum launch power

Minimum receiver sensitivity

Maximum input power

Core/Cladding size

Modal bandwidth

Distance

100 m (328 ft)

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-SX

Model number

EX-SFP-1GE-SX

Rate

1000 Mbps

Connector type

LC

Fiber count

Dual

Transmitter wavelength

850 nm

Minimum launch power

–9.5 dBm

Maximum launch power

–3 dBm

Minimum receiver sensitivity

–21 dBm

Maximum input power

0 dBm

Fiber type

MMF

Core/Cladding size

62.5/125 µm

62.5/125 µm

50/125 µm

50/125 µm

Fiber grade

FDDI

OM1

OM2

Modal bandwidth

160 MHz/km

200 MHz/km

400 MHz/km

500 MHz/km

Distance

220 m (722 ft)

275 m (902 ft)

500 m (1640 ft)

550 m (1804 ft)

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-SX-ET

Model number

EX-SFP-1GE-SX-ET

Rate

1000 Mbps

Connector type

LC

Fiber count

Dual

Transmitter wavelength

850 nm

Minimum launch power

–9.5 dBm

Maximum launch power

–3 dBm

Minimum receiver sensitivity

–21 dBm

Maximum input power

0 dBm

Fiber type

MMF

Core/Cladding size

62.5/125 µm

62.5/125 µm

50/125 µm

50/125 µm

Fiber grade

FDDI

OM1

OM2

Modal bandwidth

160 MHz/km

200 MHz/km

400 MHz/km

500 MHz/km

Distance

220 m (722 ft)

275 m (902 ft)

500 m (1640 ft)

550 m (1804 ft)

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-LX

Model number

EX-SFP-1GE-LX

Rate

1000 Mbps

Connector type

LC

Fiber count

Dual

Transmitter wavelength

1310 nm

Minimum launch power

–9.5 dBm

Maximum launch power

–3 dBm

Minimum receiver sensitivity

–25 dBm

Maximum input power

–3 dBm

Fiber type

SMF

Core/Cladding size

9/125 µm

Modal bandwidth

Distance

10 km (6.2 miles)

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-BX-U

Model number

EX-SFP-GE10KT13R14

Rate

1000 Mbps

Connector type

LC

Fiber count

Single

Transmitter wavelength

1310 nm

Receiver wavelength

1490 nm

Minimum launch power

–9 dBm

Maximum launch power

–3 dBm

Minimum receiver sensitivity

–30 dBm

Maximum input power

–3 dBm

Fiber type

SMF

Core/Cladding size

9/125 µm

Modal bandwidth

Distance

10 km (6.2 miles)

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-BX-D

Model number

EX-SFP-GE10KT14R13

Rate

1000 Mbps

Connector type

LC

Fiber count

Single

Transmitter wavelength

1490 nm

Receiver wavelength

1310 nm

Minimum launch power

–9 dBm

Maximum launch power

–3 dBm

Minimum receiver sensitivity

–30 dBm

Maximum input power

–3 dBm

Fiber type

SMF

Core/Cladding size

9/125 µm

Modal bandwidth

Distance

10 km (6.2 miles)

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-BX-U

Model number

EX-SFP-GE10KT13R15

Rate

1000 Mbps

Connector type

LC

Fiber count

Single

Transmitter wavelength

1310 nm

Receiver wavelength

1550 nm

Minimum launch power

–9 dBm

Maximum launch power

–3 dBm

Minimum receiver sensitivity

–21 dBm

Maximum input power

–3 dBm

Fiber type

SMF

Core/Cladding size

9/125 µm

Modal bandwidth

Distance

10 km (6.2 miles)

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-BX-D

Model number

EX-SFP-GE10KT15R13

Rate

1000 Mbps

Connector type

LC

Fiber count

Single

Transmitter wavelength

1550 nm

Receiver wavelength

1310 nm

Minimum launch power

–9 dBm

Maximum launch power

–3 dBm

Minimum receiver sensitivity

–21 dBm

Maximum input power

–3 dBm

Fiber type

SMF

Core/Cladding size

9/125 µm

Modal bandwidth

Distance

10 km (6.2 miles)

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-BX-U

Model number

EX-SFP-GE40KT13R15

Rate

1000 Mbps

Connector type

LC

Fiber count

Single

Transmitter wavelength

1310 nm

Receiver wavelength

1550 nm

Minimum launch power

–6.5 dBm

Maximum launch power

2 dBm

Minimum receiver sensitivity

–23 dBm

Maximum input power

–3 dBm

Fiber type

SMF

Core/Cladding size

9/125 µm

Modal bandwidth

Distance

40 km (24.8 miles)

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-BX-D

Model number

EX-SFP-GE40KT15R13

Rate

1000 Mbps

Connector type

LC

Fiber count

Single

Transmitter wavelength

1550 nm

Receiver wavelength

1310 nm

Minimum launch power

–6.5 dBm

Maximum launch power

2 dBm

Minimum receiver sensitivity

–23 dBm

Maximum input power

–3 dBm

Fiber type

SMF

Core/Cladding size

9/125 µm

Modal bandwidth

Distance

40 km (24.8 miles)

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-LX

Model number

EX-SFP-1GE-LX40K

Rate

1000 Mbps

Connector type

LC

Fiber count

Double

Transmitter wavelength

1310 nm

Minimum launch power

–14 dBm

Maximum launch power

–8 dBm

Minimum receiver sensitivity

–45 dBm

Maximum input power

–3 dBm

Fiber type

SMF

Core/Cladding size

9/125 µm

Modal bandwidth

Distance

40 km (24.8 miles)

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-LH (or 1000BASE-ZX)

Model number

EX-SFP-1GE-LH

Rate

1000 Mbps

Connector type

LC

Fiber count

Dual

Transmitter wavelength

1550 nm

Minimum launch power

–2 dBm

Maximum launch power

5 dBm

Minimum receiver sensitivity

–25 dBm

Maximum input power

–3 dBm

Fiber type

SMF

Core/Cladding size

9/125 µm

Modal bandwidth

Distance

70 km (43.5 miles)

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-LX

Model number

EX-SFP-GE80KCW1470

Rate

1000 Mbps

Connector type

LC

Fiber count

Single

Transmitter wavelength

1470 nm

Minimum launch power

0 dBm

Maximum launch power

5 dBm

Minimum receiver sensitivity

–32 dBm

Maximum input power

–8 dBm

Fiber type

SMF

Core/Cladding size

9/125 μm

Modal bandwidth

Distance

80 km (49.7 miles)

DOM support

Available

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-LX

Model number

EX-SFP-GE80KCW1490

Rate

1000 Mbps

Connector type

LC

Fiber count

Single

Transmitter wavelength

1490 nm

Minimum launch power

0 dBm

Maximum launch power

5 dBm

Minimum receiver sensitivity

–32 dBm

Maximum input power

–8 dBm

Fiber type

SMF

Core/Cladding size

9/125 μm

Modal bandwidth

Distance

80 km (49.7 miles)

DOM support

Available

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-LX

Model number

EX-SFP-GE80KCW1510

Rate

1000 Mbps

Connector type

LC

Fiber count

Single

Transmitter wavelength

1510 nm

Minimum launch power

0 dBm

Maximum launch power

5 dBm

Minimum receiver sensitivity

–32 dBm

Maximum input power

–8 dBm

Fiber type

SMF

Core/Cladding size

9/125 μm

Modal bandwidth

Distance

80 km (49.7 miles)

DOM support

Available

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-LX

Model number

EX-SFP-GE80KCW1530

Rate

1000 Mbps

Connector type

LC

Fiber count

Single

Transmitter wavelength

1530 nm

Minimum launch power

0 dBm

Maximum launch power

5 dBm

Minimum receiver sensitivity

–32 dBm

Maximum input power

–8 dBm

Fiber type

SMF

Core/Cladding size

9/125 μm

Modal bandwidth

Distance

80 km (49.7 miles)

DOM support

Available

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-LX

Model number

EX-SFP-GE80KCW1550

Rate

1000 Mbps

Connector type

LC

Fiber count

Single

Transmitter wavelength

1550 nm

Minimum launch power

0 dBm

Maximum launch power

5 dBm

Minimum receiver sensitivity

–32 dBm

Maximum input power

–8 dBm

Fiber type

SMF

Core/Cladding size

9/125 μm

Modal bandwidth

Distance

80 km (49.7 miles)

DOM support

Available

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-LX

Model number

EX-SFP-GE80KCW1570

Rate

1000 Mbps

Connector type

LC

Fiber count

Single

Transmitter wavelength

1570 nm

Minimum launch power

0 dBm

Maximum launch power

5 dBm

Minimum receiver sensitivity

–32 dBm

Maximum input power

–8 dBm

Fiber type

SMF

Core/Cladding size

9/125 μm

Modal bandwidth

Distance

80 km (49.7 miles)

DOM support

Available

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-LX

Model number

EX-SFP-GE80KCW1590

Rate

1000 Mbps

Connector type

LC

Fiber count

Single

Transmitter wavelength

1590 nm

Minimum launch power

0 dBm

Maximum launch power

5 dBm

Minimum receiver sensitivity

–32 dBm

Maximum input power

–8 dBm

Fiber type

SMF

Core/Cladding size

9/125 μm

Modal bandwidth

Distance

80 km (49.7 miles)

DOM support

Available

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

1000BASE-LX

Model number

EX-SFP-GE80KCW1610

Rate

1000 Mbps

Connector type

LC

Fiber count

Single

Transmitter wavelength

1610 nm

Minimum launch power

0 dBm

Maximum launch power

5 dBm

Minimum receiver sensitivity

–32 dBm

Maximum input power

–8 dBm

Fiber type

SMF

Core/Cladding size

9/125 μm

Modal bandwidth

Distance

80 km (49.7 miles)

DOM support

Available

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

Table 2: Optical Interface Support for Gigabit Ethernet SFP+ Transceivers in NFX250 Devices

Ethernet Standard

Specification

Value

10GBASE-USR

Model number

EX-SFP-10GE-USR

Rate

10 Gbps

Connector type

LC

Fiber count

Dual

Transmitter wavelength

850 nm

Minimum launch power

–7.3 dBm

Maximum launch power

–1.3 dBm

Minimum receiver sensitivity

–11.1 dBm

Maximum input power

–1.0 dBm

Fiber type

MMF

Core/Cladding size

62.5/125 µm

50/125 µm

50/125 µm

Fiber grade

OM1

OM3

OM3

Modal bandwidth

200 MHz/km

500 MHz/km

1500 MHz/km

Distance

10 m (32.8 ft)

30 m (98.4 ft)

100 m (328 ft)

DOM support

Available

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

10GBASE-SR

Model number

EX-SFP-10GE-SR

Rate

10 Gbps

Connector type

LC

Fiber count

Dual

Transmitter wavelength

850 nm

Minimum launch power

–7.3 dBm

Maximum launch power

–1 dBm

Minimum receiver sensitivity

–9.9 dBm

Maximum input power

–1 dBm

Fiber type

MMF

Core/Cladding size

62.5/125 µm

62.5/125 µm

50/125 µm

50/125 µm

50/125 µm

Fiber grade

FDDI

OM1

OM2

OM3

Modal bandwidth

160 MHz/km

200 MHz/km

400 MHz/km

500 MHz/km

1500 MHz/km

Distance

26 m (85 ft)

33 m (108 ft)

66 m (216 ft)

82 m (269 ft)

300 m (984 ft)

DOM support

Available

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

10GBASE-LR

Model number

EX-SFP-10GE-LR

Rate

10 Gbps

Connector type

LC

Fiber count

Dual

Transmitter wavelength

1310 nm

Minimum launch power

–8.2 dBm

Maximum launch power

0.5 dBm

Minimum receiver sensitivity

–18 dBm

Maximum input power

0.5 dBm

Fiber type

SMF

Core/Cladding size

9/125 µm

Modal bandwidth

Distance

10 km (6.2 miles)

DOM support

Available

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

10GBASE-ER

Model number

EX-SFP-10GE-ER

Rate

10 Gbps

Connector type

LC

Fiber count

Dual

Transmitter wavelength

1550 nm

Minimum launch power

–4.7 dBm

Maximum launch power

4 dBm

Minimum receiver sensitivity

–11.3 dBm

Maximum input power

–1 dBm

Fiber type

SMF

Core/Cladding size

9/125 µm

Modal bandwidth

Distance

40 km (24.8 miles)

DOM support

Available

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

10GBASE-ZR

Model number

EX-SFP-10GE-ZR

Rate

10 Gbps

Connector type

LC

Fiber count

Dual

Transmitter wavelength

1550 nm

Minimum launch power

0 dBm

Maximum launch power

5 dBm

Minimum receiver sensitivity

–20 dBm

Maximum input power

–8 dBm

Fiber type

SMF

Core/Cladding size

9/125 µm

Modal bandwidth

Distance

80 km (49.7 miles)

DOM support

Available

Software required

Junos OS for NFX250 Devices, Release 15.1X53-D40 or later

Support for Virtual Chassis configuration

Yes

SFP+ Direct Attach Cables for NFX250 Devices

Small form-factor pluggable plus transceiver (SFP+) direct attach copper (DAC) cables, also known as Twinax cables, are suitable for in-rack connections between servers and switches. They are suitable for short distances of up to 23 ft (7 m), making them ideal for highly cost-effective networking connectivity within a rack and between adjacent racks.

This topic describes:

Cable Specifications

NFX250 devices support SFP+ passive DAC cables. The passive Twinax cable is a straight cable with no active electronic components. NFX250 devices support 1 m, 3 m, and 5 m long SFP+ passive DAC cables.

Note:

We recommend that you use only SFP+ DAC cables purchased from Juniper Networks with your Juniper Networks device.

CAUTION:

If you face a problem running a Juniper Networks device that uses a third-party optic or cable, the Juniper Networks Technical Assistance Center (JTAC) can help you diagnose the source of the problem. Your JTAC engineer might recommend that you check the third-party optic or cable and potentially replace it with an equivalent Juniper Networks optic or cable that is qualified for the device.

The cables are hot-removable and hot-insertable: You can remove and replace them without powering off the switch or disrupting switch functions. A cable comprises a low-voltage cable assembly that connects directly into two SFP+ ports, one at each end of the cable. The cables use high-performance integrated duplex serial data links for bidirectional communication and are designed for data rates of up to 10 Gbps.

Table 3 describes the cable specifications.

Table 3: SFP+ Direct Attach Copper Cable Specifications

Model Number

Specification

Value

EX-SFP-10GE-DAC-1M

Rate

10-Gbps full-duplex serial transmission

Connector type

SFP+ passive Twinax cable assembly

Supply voltage

3.3 V

Power consumption (per end)

0.57 W

Storage temperature

–40° C through 85° C

Cable type

Twinax

Wire AWG

30 AWG

Minimum cable bend radius

1 in. (2.54 cm)

Cable characteristic impedance

100 ohms

Crosstalk between pairs

2% maximum

Time delay

1.31 nsec/ft

Length

1 m (3.3 ft )

EX-SFP-10GE-DAC-3M

Rate

10-Gbps full-duplex serial transmission

Connector type

SFP+ passive Twinax cable assembly

Supply voltage

3.3 V

Power consumption (per end)

0.57 W

Storage temperature

–40° C through 85° C

Cable type

Twinax

Wire AWG

30 AWG

Minimum cable bend radius

1 in. (2.54 cm)

Cable characteristic impedance

100 ohms

Crosstalk between pairs

2% maximum

Time delay

1.31 nsec/ft

Length

3 m (9.9 ft)

EX-SFP-10GE-DAC-5M

Rate

10-Gbps full-duplex serial transmission

Connector type

SFP+ passive Twinax cable assembly

Supply voltage

3.3 V

Power consumption (per end)

0.57 W

Storage temperature

–40° C through 85° C

Cable type

Twinax

Wire AWG

24 AWG

Minimum cable bend radius

1 in. (2.54 cm)

Cable characteristic impedance

100 ohms

Crosstalk between pairs

2% maximum

Time delay

1.31 nsec/ft

Length

5 m (16.4 ft)

Standards Supported by These Cables

The cables comply with the following standards:

Understanding NFX250 Devices Fiber-Optic Cable Signal Loss, Attenuation, and Dispersion

To determine the power budget and power margin needed for fiber-optic connections, you need to understand how signal loss, attenuation, and dispersion affect transmission. The NFX250 devices use various types of network cable, including multimode and single-mode fiber-optic cables.

Signal Loss in Multimode and Single-Mode Fiber-Optic Cables

Multimode fiber is large enough in diameter to allow rays of light to reflect internally (bounce off the walls of the fiber). Interfaces with multimode optics typically use LEDs as light sources. However, LEDs are not coherent light sources. They spray varying wavelengths of light into the multimode fiber, which reflects the light at different angles. Light rays travel in jagged lines through a multimode fiber, causing signal dispersion. When light traveling in the fiber core radiates into the fiber cladding (layers of lower refractive index material in close contact with a core material of higher refractive index), higher-order mode loss occurs. Together, these factors reduce the transmission distance of multimode fiber compared to that of single-mode fiber.

Single-mode fiber is so small in diameter that rays of light reflect internally through one layer only. Interfaces with single-mode optics use lasers as light sources. Lasers generate a single wavelength of light, which travels in a straight line through the single-mode fiber. Compared to multimode fiber, single-mode fiber has a higher bandwidth and can carry signals for longer distances. It is consequently more expensive.

For information about the maximum transmission distance and supported wavelength range for the types of single-mode and multimode fiber-optic cables that are connected to the NFX250 devices, see Pluggable Transceivers Supported on NFX250 Devices. Exceeding the maximum transmission distances can result in significant signal loss, which causes unreliable transmission.

Attenuation and Dispersion in Fiber-Optic Cable

An optical data link functions correctly provided that modulated light reaching the receiver has enough power to be demodulated correctly. Attenuation is the reduction in strength of the light signal during transmission. Passive media components such as cables, cable splices, and connectors cause attenuation. Although attenuation is significantly lower for optical fiber than for other media, it still occurs in both multimode and single-mode transmission. An efficient optical data link must transmit enough light to overcome attenuation.

Dispersion is the spreading of the signal over time. The following two types of dispersion can affect signal transmission through an optical data link:

  • Chromatic dispersion, which is the spreading of the signal over time caused by the different speeds of light rays.

  • Modal dispersion, which is the spreading of the signal over time caused by the different propagation modes in the fiber.

For multimode transmission, modal dispersion, rather than chromatic dispersion or attenuation, usually limits the maximum bit rate and link length. For single-mode transmission, modal dispersion is not a factor. However, at higher bit rates and over longer distances, chromatic dispersion limits the maximum link length.

An efficient optical data link must have enough light to exceed the minimum power that the receiver requires to operate within its specifications. In addition, the total dispersion must be within the limits specified for the type of link in Telcordia Technologies document GR-253-CORE (Section 4.3) and International Telecommunications Union (ITU) document G.957.

When chromatic dispersion is at the maximum allowed, its effect can be considered as a power penalty in the power budget. The optical power budget must allow for the sum of component attenuation, power penalties (including those from dispersion), and a safety margin for unexpected losses.

Calculating the Fiber-Optic Cable Power Budget for an NFX250 Device

Calculate the link's power budget when planning fiber-optic cable layout and distances to ensure that fiber-optic connections have sufficient power for correct operation. The power budget is the maximum amount of power the link can transmit. When you calculate the power budget, you use a worst-case analysis to provide a margin of error, even though all the parts of an actual system do not operate at the worst-case levels.

To calculate the worst-case estimate for fiber-optic cable power budget (PB) for the link:

  1. Determine values for the link's minimum transmitter power (PT) and minimum receiver sensitivity (PR). For example, here, (PT) and (PR) are measured in decibels, and decibels are referenced to 1 milliwatt (dBm).

    PT = –15 dBm

    PR = –28 dBm

    Note:

    See the specifications for your transmitter and receiver to find the minimum transmitter power and minimum receiver sensitivity.

  2. Calculate the power budget (PB) by subtracting (PR) from (PT):

    –15 dBm – (–28 dBm) = 13 dBm

Calculating the Fiber-Optic Cable Power Margin for an NFX250 Device

Before you begin to calculate the power margin:

Calculate the link's power margin when planning fiber-optic cable layout and distances to ensure that fiber-optic connections have sufficient signal power to overcome system losses and still satisfy the minimum input requirements of the receiver for the required performance level. The power margin (PM ) is the amount of power available after attenuation or link loss (LL) has been subtracted from the power budget (PB).

When you calculate the power margin, you use a worst-case analysis to provide a margin of error, even though all the parts of an actual system do not operate at worst-case levels. A power margin (PM ) greater than zero indicates that the power budget is sufficient to operate the receiver and that it does not exceed the maximum receiver input power. This means the link will work. A (PM) that is zero or negative indicates insufficient power to operate the receiver. See the specification for your receiver to find the maximum receiver input power.

To calculate the worst-case estimate for the power margin (PM) for the link:

  1. Determine the maximum value for link loss (LL) by adding estimated values for applicable link-loss factors—for example, use the sample values for various factors as provided in Table 4 (here, the link is 2 km long and multimode, and the (PB) is 13 dBm):
    Table 4: Estimated Values for Factors Causing Link Loss

    Link-Loss Factor

    Estimated Link-Loss Value

    Sample Link Loss (LL) Calculation Values

    Higher-order mode losses

    Multimode—0.5 dBm

    0.5 dBm

    Single-mode—None

    0 dBm

    Modal and chromatic dispersion

    Multimode—None, if product of bandwidth and distance is less than 500 MHz/km

    0 dBm

    Single-mode—None

    0 dBm

    Connector

    0.5 dBm

    This example assumes five connectors. Loss for five connectors: 5 (0.5 dBm) = 2.5 dBm.

    Splice

    0.5 dBm

    This example assumes two splices. Loss for two splices: 2 (0.5 dBm) = 1 dBm.

    Fiber attenuation

    Multimode—1 dBm/km

    This example assumes the link is 2 km long. Fiber attenuation for 2 km: 2 km (1 dBm/km) = 2 dBm.

    Single-mode—0.5 dBm/km

    This example assumes the link is 2 km long. Fiber attenuation for 2 km: 2 km (0.5 dBm/km) = 1 dBm.

    Clock Recovery Module (CRM)

    1 dBm

    1 dBm

    Note:

    For information about the actual amount of signal loss caused by equipment and other factors, see your vendor documentation for that equipment.

  2. Calculate the (PM) by subtracting (LL) from (PB):

    PB– LL = PM

    13 dBm – 0.5 dBm [HOL] – 5 (0.5 dBm) – 2 (0.5 dBm) – 2 km (1.0 dBm/km) – 1 dB [CRM] = PM

    13 dBm – 0.5 dBm – 2.5 dBm – 1 dBm – 2 dBm – 1 dBm = PM

    PM = 6 dBm

    The calculated power margin is greater than zero, indicating that the link has sufficient power for transmission. Also, the power margin value does not exceed the maximum receiver input power. Refer to the specifications for your receiver to find the maximum receiver input power.