EX9200 Network Cable and Transceiver Planning
Pluggable Transceivers Supported on EX9200 Switches
The line cards in EX9200 switches support 1-gigabit Ethernet small form-factor pluggable (SFP), 1-gigabit Fast Ethernet SFP, 10-gigabit small form-factor pluggable plus (SFP+), 40-gigabit quad small form-factor pluggable plus (QSFP+), and 100-gigabit C form-factor pluggable (CFP) transceivers.
You can find the list of transceivers supported on EX9204 switches and information about those transceivers at the Hardware Compatibility Tool page for EX9204.
You can find the list of transceivers supported on EX9208 switches and information about those transceivers at the Hardware Compatibility Tool page for EX9208.
You can find the list of transceivers supported on EX9214 switches and information about those transceivers at the Hardware Compatibility Tool page for EX9214.
We recommend that you use only optical transceivers and optical connectors purchased from Juniper Networks with your Juniper Networks device.
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 Gigabit Ethernet SFP, SFP+, and QSFP+ transceivers and the 100GBASE-LR4 CFP transceivers installed in EX9200 switches support digital optical monitoring (DOM): You can view the diagnostic details for these transceivers by issuing the operational mode CLI command show interfaces diagnostics optics.
Understanding EX Series Switches 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. EX Series switches use various types of network cable, including multimode and single-mode fiber-optic cable.
Signal Loss in Multimode and Single-Mode Fiber-Optic Cable
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 (HOL) 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.
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 EX Series Devices
To ensure that fiber-optic connections have sufficient power for correct operation, 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:
- 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 referred to one milliwatt (dBm).
PT = – 15 dBm
PR = – 28 dBm
See the specifications for your transmitter and receiver to find the minimum transmitter power and minimum receiver sensitivity.
- Calculate the power budget (PB) by subtracting (PR) from (PT):
– 15 dBm – (–28 dBm) = 13 dBm
Calculating the Fiber-Optic Cable Power Margin for EX Series Devices
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.
Before you begin to calculate the power margin:
Calculate the power budget (see Calculating the Fiber-Optic Cable Power Budget for EX Series Devices).
To calculate the worst-case estimate for the power margin (PM) for the link:
- 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 1 (here, the link
is 2 km long and multimode, and the (PB) is 13 dBm):
Estimated Link-Loss Value
Sample (LL) Calculation Values
Higher-order mode losses (HOL)
Modal and chromatic dispersion
Multimode—None, if product of bandwidth and distance is less than 500 MHz/km
This example assumes 5 connectors. Loss for 5 connectors:
(5) * (0.5 dBm) = 2.5 dBm
This example assumes 2 splices. Loss for two splices:
(2) * (0.5 dBm) = 1 dBm
Single mode—0.5 dBm/km
This example assumes the link is 2 km long. Fiber attenuation for 2 km:
(2 km) * (1.0 dBm/km) = 2 dBm
(2 km) * (0.5 dBm/km) = 1 dBm
Clock Recovery Module (CRM)
For information about the actual amount of signal loss caused by equipment and other factors, see your vendor documentation for that equipment.
- 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 specification for your receiver to find the maximum receiver input power.