ON THIS PAGE
EX4600 Network Cable and Transceiver Planning
Determining Interface Support for an EX4600 Switch
The 24 small form-factor pluggable (SFP) network ports on EX4600 switches support 10-Gigabit Ethernet transceivers and direct-attach copper (DAC) cables. The switch also supplies four quad small form-factor pluggable plus (QSFP+) ports for use as uplinks. These 40-Gigabit Ethernet ports support QSFP+ transceivers, QSFP+ DAC cables, and DAC breakout cables (DACBO). Each QSFP+ port on an EX4600 switch can be configured to operate as 10-Gigabit Ethernet interface by using a breakout cable or as a single 40-Gigabit Ethernet interface. The ports on an EX4600 switch are disabled by default. You enable a port through the CLI.
Figure 1 shows the different ports available on the EX4600 switch.
Electrostatic discharge (ESD) terminal
40 GbE ports (4)
10 G ports (24)
Expansion module bays with cover panels (2)
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 EX4600 is located at https://pathfinder.juniper.net/hct/product/#prd=EX4600.
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+ Transceivers on EX4600 Series Switches
The 40-Gigabit Ethernet QSFP+ transceivers that are used in EX Series switches use 12-ribbon multimode fiber crossover cables with socket MPO/UP, MPO/UPC, or MPO/APC connectors. The fiber can be either OM3 or OM4. These cables are not sold by Juniper Networks.
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+, ensure that the proper polarity is maintained through the cable plant.
Table 1: QSFP+ MPO Cable Signals
Table 2: QSFP+ MPO Fiber-Optic Crossover Cable Pinouts
Network Cable Specifications for EX4600 Switches
EX4600 switches have interfaces that use various types of network cables.
Table 3 lists the
specifications for the cables that connect the console (
CON) and management (
to management devices.
The EX4600 can be configured with SFP management ports that support 1000BASE-SX transceivers.
Table 3: Cable Specifications for Switch-to-Management-Device Connections
Ports on EX4600 Switches
RJ-45 Console (
RS-232 (EIA-232) serial cable
One 7-foot (2.13-meter) length RJ-45 patch cable and RJ-45 to DB-9 adapter
7 ft (2.13 m)
Category 5 cable or equivalent suitable for 1000BASE-T operation
One 7-foot (2.13-meter) length RJ-45 patch cable
328 feet (100 meters)
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 4 (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.