ACX710 Network Cable and Transceiver Planning
Determining Transceiver Support for ACX710
You can find information about the pluggable transceivers and connector types that are supported on your Juniper Networks device by using the Hardware Compatibility Tool. The tool also documents the optical and cable characteristics, where applicable, for each transceiver. You can search for transceivers by product—the tool displays all the transceivers supported on that device—or by category, interface speed, or type. The list of supported transceivers for the ACX710 is located at https://apps.juniper.net/hct/product/#prd=ACX710.
The Juniper Networks Technical Assistance Center (JTAC) provides complete support for Juniper-supplied optical modules and cables. However, JTAC does not provide support for third-party optical modules and cables that are not qualified or supplied by Juniper Networks. If you face a problem running a Juniper device that uses third-party optical modules or cables, JTAC may help you diagnose host-related issues if the observed issue is not, in the opinion of JTAC, related to the use of the third-party optical modules or cables. Your JTAC engineer will likely request that you check the third-party optical module or cable and, if required, replace it with an equivalent Juniper-qualified component.
Use of third-party optical modules with high-power consumption (for example, coherent ZR or ZR+) can potentially cause thermal damage to or reduce the lifespan of the host equipment. Any damage to the host equipment due to the use of third-party optical modules or cables is the users’ responsibility. Juniper Networks will accept no liability for any damage caused due to such use.
For the I-temp and C-temp transceivers that are supported on ACX710, see the following maximum ambient temperature values that are supported:
Supports I-temp SFP, SFP+, and SFP28 transceivers up to 1.5W in full working temperature range (-40° C to +65° C).
Supports I-temp SFP, SFP+, and SFP28 transceivers up to 2W, with 10° C degradation in maximum working temperature range (-40° C to +55° C).
Supports I-temp QSFP+ and QSFP28 transceivers up to 4.5W in full working temperature range (-40° C to +65° C).
Supports C-temp SFP, SFP+, and SFP28 transceivers up to 1W, with 10° C degradation in maximum working temperature range (0° C to +55° C).
Supports C-temp SFP, SFP+, and SFP28 transceivers up to 1.5W, with 15° C degradation in maximum working temperature range (0° C to +50° C).
Supports C-temp SFP, SFP+, and SFP28 transceivers up to 2W, with 20° C degradation in maximum working temperature range (0° C to +45° C).
Supports C-temp QSFP+ and QSFP28 transceivers up to 4.5W, with 10° C degradation in maximum working temperature range (0° C to +55° C).
Cable Specifications for QSFP+ and QSFP28 Transceivers
The 40GbE quad small form-factor pluggable plus (QSFP+) and 100GbE quad small form-factor pluggable 28 (QSFP28) transceivers that are used in ACX Series routers use 12-ribbon multimode fiber crossover cables with MPO socket connectors (SR4 optics only). The fiber can be either OM3 or OM4. Juniper Networks does not sell these cables.
To maintain agency approvals, use only a properly constructed, shielded cable.
Ensure that you order cables with the correct polarity. Vendors refer to these crossover cables as key up to key up, latch up to latch up, Type B, or Method B. If you are using patch panels between two QSFP+ transceivers or two QSFP28 transceivers, ensure that the proper polarity is maintained through the cable plant.
Table 1 describes the signals on each fiber. Table 2 shows the pin-to-pin connections for proper polarity.
Fiber |
Signal |
|---|---|
1 |
Tx0 (Transmit) |
2 |
Tx1 (Transmit) |
3 |
Tx2 (Transmit) |
4 |
Tx3 (Transmit) |
5 |
Unused |
6 |
Unused |
7 |
Unused |
8 |
Unused |
9 |
Rx3 (Receive) |
10 |
Rx2 (Receive) |
11 |
Rx1 (Receive) |
12 |
Rx0 (Receive) |
Pin |
Pin |
|---|---|
1 |
12 |
2 |
11 |
3 |
10 |
4 |
9 |
5 |
8 |
6 |
7 |
7 |
6 |
8 |
5 |
9 |
4 |
10 |
3 |
11 |
2 |
12 |
1 |
Calculating Power Budget and Power Margin for Fiber-Optic Cables
Use the information in this topic and the specifications for your optical interface to calculate the power budget and power margin for fiber-optic cables.
You can use the Hardware Compatibility Tool to find information about the pluggable transceivers supported on your Juniper Networks device.
To calculate the power budget and power margin, perform the following tasks:
- How to Calculate Power Budget for Fiber-Optic Cables
- How to Calculate Power Margin for Fiber-Optic Cables
How to Calculate Power Budget for Fiber-Optic Cables
To ensure that fiber-optic connections have sufficient power for correct operation, you need to calculate the link's power budget, which is the maximum amount of power it 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 of power budget (PB), you assume minimum transmitter power (PT) and minimum receiver sensitivity (PR):
PB = PT – PR
The following hypothetical power budget equation uses values measured in decibels (dB) and decibels referred to one milliwatt (dBm):
PB = PT – PR
PB = –15 dBm – (–28 dBm)
PB = 13 dB
How to Calculate Power Margin for Fiber-Optic Cables
After calculating a link's power budget, you can calculate the power margin (PM), which represents the amount of power available after subtracting attenuation or link loss (LL) from the power budget (PB). A worst-case estimate of PM assumes maximum LL:
PM = PB – LL
PM greater than zero indicates that the power budget is sufficient to operate the receiver.
Factors that can cause link loss include higher-order mode losses, modal and chromatic dispersion, connectors, splices, and fiber attenuation. Table 3 lists an estimated amount of loss for the factors used in the following sample calculations. For information about the actual amount of signal loss caused by equipment and other factors, refer to vendor documentation.
Link-Loss Factor |
Estimated Link-Loss Value |
|---|---|
Higher-order mode losses |
Single mode—None Multimode—0.5 dB |
Modal and chromatic dispersion |
Single mode—None Multimode—None, if product of bandwidth and distance is less than 500 MHz-km |
Faulty connector |
0.5 dB |
Splice |
0.5 dB |
Fiber attenuation |
Single mode—0.5 dB/km Multimode—1 dB/km |
The following sample calculation for a 2-km-long multimode link with a power budget (PB) of 13 dB uses the estimated values from Table 3. This example calculates link loss (LL) as the sum of fiber attenuation (2 km @ 1 dB/km, or 2 dB) and loss for five connectors (0.5 dB per connector, or 2.5 dB) and two splices (0.5 dB per splice, or 1 dB) as well as higher-order mode losses (0.5 dB). The power margin (PM) is calculated as follows:
PM = PB – LL
PM = 13 dB – 2 km (1 dB/km) – 5 (0.5 dB) – 2 (0.5 dB) – 0.5 dB
PM = 13 dB – 2 dB – 2.5 dB – 1 dB – 0.5 dB
PM = 7 dB
The following sample calculation for an 8-km-long single-mode link with a power budget (PB) of 13 dB uses the estimated values from Table 3. This example calculates link loss (LL) as the sum of fiber attenuation (8 km @ 0.5 dB/km, or 4 dB) and loss for seven connectors (0.5 dB per connector, or 3.5 dB). The power margin (PM) is calculated as follows:
PM = PB – LL
PM = 13 dB – 8 km (0.5 dB/km) – 7(0.5 dB)
PM = 13 dB – 4 dB – 3.5 dB
PM = 5.5 dB
In both examples, the calculated power margin is greater than zero, indicating that the link has sufficient power for transmission and does not exceed the maximum receiver input power.
Fiber-Optic Cable Signal Loss, Attenuation, and Dispersion
- Signal Loss in Multimode and Single-Mode Fiber-Optic Cable
- Attenuation and Dispersion in 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 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, higher-order mode loss results. Together these factors limit the transmission distance of multimode fiber compared with single-mode fiber.
Single-mode fiber is so small in diameter that rays of light can 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 with multimode fiber, single-mode fiber has higher bandwidth and can carry signals for longer distances.
Exceeding the maximum transmission distances can result in significant signal loss, which causes unreliable transmission.
Attenuation and Dispersion in Fiber-Optic Cable
Correct functioning of an optical data link depends on modulated light reaching the receiver with enough power to be demodulated correctly. Attenuation is the reduction in power of the light signal as it is transmitted. Attenuation is caused by passive media components such as cables, cable splices, and connectors. 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 have enough light available to overcome attenuation.
Dispersion is the spreading of the signal over time. The following two types of dispersion can affect an optical data link:
Chromatic dispersion—Spreading of the signal over time, resulting from the different speeds of light rays.
Modal dispersion—Spreading of the signal over time, resulting from 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 rather than modal dispersion limits 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 less than 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.