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QFX5100 Network Cable and Transceiver Planning

 

Determining Interface Support for the QFX5100 Device

All product SKUs of the QFX5100 supply quad small form-factor pluggable plus (QSFP+) ports for use as uplinks, as access ports, or as Virtual Chassis ports (VCPs). These 40 GbE ports support QSFP+ transceivers, QSFP+ direct-attach copper (DAC) cables, and DAC breakout cables (DACBO). The QFX5100-48S has 6 QSFP+ ports; the QFX5100-96S has 8 QSFP+ ports; the QFX5100-24Q has 24 built-in QSFP+ ports that can all be used as uplinks. The You can also add two QFX-EM-4Q expansion modules to the QFX5100-24Q for additional QSFP+ uplink ports. Each QSFP+ port on a QFX5100-24Q can be configured to operate as 10-Gigabit Ethernet interface by using a breakout cable or as a single 40-Gigabit Ethernet interface. See Configuring the QSFP+ Port Type on QFX5100 Devices for more information.

On all QFX5100 product SKUs, the ports are enabled by default and the default config adds the ports to the default VLAN.

Downlink ports are product SKU-specific:

  • QFX5100-96S–has 96 small form-factor pluggable plus (SFP+) ports that support SFP and SFP+ transceivers, as well as DAC cables.

  • QFX5100-48S–has 48 SFP+ ports that support SFP and SFP+ transceivers, as well as DAC cables.

  • QFX5100-48T–has 6 QSFP+ uplink ports.

  • QFX5100-24Q–has 24 QSFP+ access ports that can be configured to operate as 10-Gigabit Ethernet interfaces or as a single 40-Gigabit Ethernet interface.

  • QFX5100-24Q-AA–has 24 QSFP+ access ports that can be configured to operate as 10-Gigabit Ethernet interfaces or as a single 40-Gigabit Ethernet interface.

Figure 1 shows the location of SFP+ and QSFP+ ports for the QFX5100-96S, Figure 2 shows these ports for the QFX5100-48S device, Figure 3 shows the RJ45 and QSFP+ ports for the QFX5100-48T device, and Figure 4 shows the location of QSFP+ ports for the QFX5100-24Q device.

Figure 1: Port Panel QFX5100-96S Device
Port Panel QFX5100-96S Device
  1
Electrostatic discharge (ESD) terminal
  3
QSFP+ uplink ports (8)
  2
SFP+ access ports (96)
 
Figure 2: Port Panel QFX5100-48S Device
Port Panel QFX5100-48S Device
  1
Electrostatic discharge (ESD) terminal
  3
QSFP+ uplink ports (6)
  2
SFP+ access ports (48)
 
Figure 3: Port Panel QFX5100-48T Device
Port Panel QFX5100-48T Device
  1
Electrostatic discharge (ESD) terminal
  3
QSFP+ uplink ports (6)
  2
RJ45 access ports (48)
 
Figure 4: Port Panel QFX5100-24Q Device
Port Panel QFX5100-24Q Device
  1
Electrostatic discharge (ESD) terminal
  3
Expansion module bays with cover panels (2)
  2
QSFP+ access or uplink ports (24)
 
Figure 5: Port Panel QFX5100-24Q-AA Device
Port Panel QFX5100-24Q-AA
Device
  1
Electrostatic discharge (ESD) terminal
  3
Expansion module bay (shows a QFX-PFA-4Q installed)
  2
QSFP+ access or uplink ports (24)
 

You can find information about the optical transceivers supported on your Juniper device by using the Hardware Compatibility Tool. In addition to transceiver and connection 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 QFX5100 is located at https://pathfinder.juniper.net/hct/product/#prd=QFX5100.

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.

Cable Specifications for QSFP+ and QSFP28 Transceivers

The 40-Gigabit Ethernet QSFP+ and 100-Gigabit Ethernet QSFP28 transceivers that are used in QFX Series switches use 12-ribbon multimode fiber crossover cables with socket MPO/UPC connectors. The fiber can be either OM3 or OM4. These cables are not sold by Juniper Networks.

Caution

To maintain agency approvals, use only a properly constructed, shielded cable.

Tip

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+ or 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.

Table 1: QSFP+ and QSFP28 Optical Module Receptacle Pinouts

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)

Table 2: QSFP+ MPO Fiber-Optic Crossover Cable Pinouts

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

Understanding QFX Series 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 QFX Series 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.

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 QFX Series, see the Hardware Compatibility Tool. 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 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.

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.

Tip

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:

  1. How to Calculate Power Budget for Fiber-Optic Cable

  2. How to Calculate Power Margin for Fiber-Optic Cable

How to Calculate Power Budget for Fiber-Optic Cable

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 Cable

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

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 to calculate 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 to calculate 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.