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PTX10008 Transceiver and Cable Specifications
Review fiber-optic cable characteristics and plan the power budget and power margin for fiber-optic cables connected to your device by using the information in the following topics.
PTX10008 Optical Transceiver and Cable Support
You can find information about the pluggable transceivers supported on your Juniper Networks device by using the Hardware Compatibility Tool. In addition to transceiver and connector type, the optical and cable characteristics—where applicable—are documented for each transceiver. The Hardware Compatibility Tool enables you to search by product, displaying all the transceivers supported on that device, or category, by interface speed or type. The list of supported transceivers for the PTX10008 is located at https://apps.juniper.net/hct/home/.
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.
PTX10008 Cable Specifications for Console and Management Connections
Table 1 lists the specifications for the cables that connect the PTX10008 router to a management device.
The PTX10008 can be configured with SFP management ports that support 1000BASE-SX transceivers.
Table 1: Cable Specifications for Console and Management Connections for the PTX10008 Routers
Port on PTX10008 Router
RS-232 (EIA-232) serial cable
One 7-foot (2.13-meter) long RJ-45 patch cable and RJ-45 to DB-9 adapter
Category 5 cable or equivalent suitable for 1000BASE-T operation
One 7-foot (2.13-meter) long RJ-45 patch cable
PTX10008 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 PTX10008 router uses various types of network cables, 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 reflect 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.
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 the 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.
Calculate the Fiber-Optic Cable Power Budget for a PTX Series Router
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 the 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 referenced to 1 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 (
–15 dBm – (–28 dBm) = 13 dBm
Calculate the Fiber-Optic Cable Power Margin for a PTX Series Router
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
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 (
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.
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 2 (here, the link is 2 km long and multimode, and the (
PB) is 13 dBm).
Estimated Link Loss Value
Sample Link Loss (LL) Calculation Values
Higher-order mode losses
Modal and chromatic dispersion
Multimode—None, if product of bandwidth and distance is less than 500 MHz/km
This example assumes five connectors. Loss for five connectors: 5 (0.5 dBm) = 2.5 dBm.
This example assumes two splices. Loss for two splices: 2 (0.5 dBm) = 1 dBm.
This example assumes the link is 2 km long. Fiber attenuation for 2 km: 2 km (1 dBm/km) = 2 dBm.
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)
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– 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.