Installation Instructions

Quad (4-channel) Small Form Factor Pluggable 28 (QSFP28)
QSFP28 transceivers are hot-swappable data I/O components that allow 100 Gigabit Ethernet ports
to link with other 100 Gigabit Ethernet ports. All branded QSFP28 transceivers use LC connectors
and MPO/MTP connectors to provide precision keying and low interface losses.
Note:
QSFP28 transceivers are currently supported on the VSP 8404C and VSP 8608 chassis models
only.
For more information about QSFP28 transceivers, see QSFP28 on page 63.
Optical power considerations
When you connect the device to collocated equipment, ensure that enough optical attenuation exists
to avoid overloading the receivers of each device. You must consider the minimum attenuation
requirement based on the specifications of third-party equipment. .
Dispersion considerations for long reach
Precise engineering of transmission links is difficult; specifications and performance are often
unknown, undocumented, or impractical to measure before equipment installation. Moreover, the
skills required to perform rigorous link budget analysis are extensive. Fortunately, a simple,
straightforward approach can assure robust link performance for most optical fiber systems in which
you use Extreme Networks switches and routers.
This method uses an optical power budget, the difference between transmitter power and receiver
sensitivity, to determine whether the installed link can operate with low bit error ratio for extended
periods. The power budget must accommodate the sum of link loss (that is, attenuation), dispersion,
and system margin, described in the following paragraphs.
Link losses are the sum of cabled fiber loss, splices, and connectors, often with an allocation for
additional connectors. Cabled fiber loss is wavelength and installation dependent, and is typically in
the range of 0.20 to 0.5 dB/km. See the cable plant owner or operator for specifications of the cable
you use, particularly if the available system margin is unsatisfactory. Engineered links require
precise knowledge of the cable plant.
For long, high bit rate systems, pulse distortion, caused by the transmitter laser spectrum interaction
with fiber chromatic dispersion, reduces receiver sensitivity. Transceivers for long reach single mode
fiber systems have an associated maximum dispersion power penalty (DPP
max
) specification, which
applies to G.652 (dispersion unshifted) single mode fiber and the rated transceiver reach. The actual
power penalty that you must use is
DPP
budget
= [link length(km) / transceiver maximum reach (km)] * DPP
max
For example, if an 80 km transceiver is specified as having DPP < 3 dB, and if the actual link length
will be 40 km, DPP
budget
is one-half the maximum, or 1.5 dB.
Link operating margins are sometimes allocated for impairments such as aging, thermal, or other
environmental effects. Because of the potentially large number of factors that can degrade
performance, you can usually rely on statistics to represent these factors as a single margin value,
Optical routing design
May 2018 Installing Transceivers and Optical Components on VOSS 21