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QFX5120 Network Cable and Transceiver Planning

Pluggable Transceivers and Direct Attach Cables Supported on QFX5120 Switches

QFX5120 switches support SFP, SFP+, SFP28, QSFP+, and QSFP28 transceivers. They also support direct attach cables. You can find the list of transceivers supported on QFX5120 switches and information about those transceivers at the following pages:

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 Gigabit Ethernet transceivers installed in QFX5120 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.

Cable Specifications for QSFP+ and QSFP28 Transceivers on QFX5120 Switches

The 40GbE QSFP+ and 100GbE QSFP28 transceivers used in QFX5120 switches use 12-ribbon multimode fiber crossover cables with MPO/UP, MPO/UPC, or MPO/APC socket connectors. The fiber can be either OM3 or OM4. We do not sell these cables.

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+ ports, 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 MPO Cable Signals

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+ and QSFP28 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

How to Calculate the Fiber-Optic Cable Power Budget for QFX Series Switches

Calculate the fiber-optic data 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:

  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

How to Calculate the Fiber-Optic Cable Power Margin for QFX Series Switches

Before you calculate the power margin, calculate the power budget. See How to Calculate the Fiber-Optic Cable Power Budget for QFX Series Switches.

Calculate the fiber-optic data 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) is 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 power margin (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 3 (here, the link is 2 km long and multimode, and the power margin (PM) is 13 dBm).
    Table 3: Estimated Values for Factors Causing Link Loss

    Link-Loss Factor

    Estimated Link Loss Value

    Sample Link Loss 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 the sum 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 x (0.5  dBm) – 2 (0.5 dBm) – 2 km (1.0 dBm/km) – 1 dB [CRM] = PM

    13 dB m – 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.