White paper
Fiber backbone cabling in buildings
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Contents
Introduction3
Backbone cabling speeds
3
Optical fiber in the backbone
3
10Gb/s optical fiber backbone
3
Migrating to 40 Gbps and 100 Gbps
4
Backbone distances
5
Existing installations and support for 40Gbps and 100Gbps
6
New installations and support for 40Gbps and 100Gbps
6
Conclusion6
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Introduction
Until recently, the horizontal cabling in most buildings was
designed to support speeds up to 1 Gbps to the desk, and
1000BASE-T was considered ample bandwidth for horizontal
applications in Enterprise buildings. Today, however, developments
in wireless technologies are pushing the horizontal bandwidth
beyond 1 Gbps, and the broad adoption of these technologies
will have a significant impact towards adoption of faster speeds
elsewhere in the horizontal and backbone network.
The newest generation of IEEE 802.11ac Wi-Fi access points is
capable of supporting wireless speeds up to 6.9 Gbps. In order to
provide sufficient backhaul bandwidth for these devices—and in a
clear indication that 1 Gbps speeds are no longer sufficient—the
IEEE is currently in the process of defining 2.5 Gbps and 5 Gbps
Ethernet interfaces (2.5GBASE-T and 5GBASE-T). The first commercial
implementations of these new interfaces are designed to autonegotiate up to 10 Gbps (10GBASE-T) if supported by the cabling.
Additionally, leading-edge in-building wireless systems are already
in the market, with horizontal connectivity based on 10GBASE-T
technology. As these technologies become more widely deployed, the
aggregate effects of user bandwidth are expected to drive even higher
speeds in network backbones. As a result, the bandwidth requirements
for building backbones designed to support these applications will shift
from 10 Gbps to 40 Gbps—and eventually to 100 Gbps.
Backbone cabling speeds
As a practical approach, backbones have traditionally been designed
to exceed the horizontal requirements by a factor of 10. For example,
1 Gbps backbones were designed to support 100Mb/s horizontal
requirements, and 10 Gbps backbones are currently being designed
to support up to 1 Gbps horizontal requirements. As speeds in the
horizontal migrate to 2.5 Gbps, 5 Gbps, or 10 Gbps, the backbone must
be designed to support bandwidth beyond 10 Gbps. It is therefore
recommended that new buildings or retrofits deploy a backbone that is
capable of supporting speeds of 40 Gbps and/or 100 Gbps.
Enterprise
switch
Enterprise Switch
1G
40G/100G
10G
OM1/2
OM3/4 xn
OM3
LAN
LAN
switch
Switch
LAN
LAN
switch
Switch
Cat 5e
100M
100M
100M
1G
LAN
LAN
switch
Switch
Cat 6
1G
100M
1G
1G
1G
100M
2.5/5/
10G
Cat 6A
2.5/5/
10G
ANSI/TIA-568.3-D recommends deploying a hierarchical star
topology for the backbone, with no more than two levels of crossconnections. For the simplest design, the main cross-connect (MC) in
the ER feeds directly to the horizontal cross-connect (HC) in the TR
on each floor (see figure 2). Optional intermediate cross-connects (IC)
may be positioned between the MC and HC.
10G horizontal
Category 6A recommended
Telecommunication
room (HC)
40G or 100G backbone
OM4 recommended
Equipment
room (MC)
Figure 2. Building backbone cabling system
The standard recognized transmission media for backbone cabling
comprise multimode and singlemode fiber. Laser-optimized
50/125µm (OM3 and OM4) multimode fiber is recommended and is
typically installed for 10 Gbps building backbones up to 300 meters
and 550 meters, respectively, based on the lower electronics costs
when compared with singlemode fiber. Singlemode fiber is typically
installed where the channel lengths are expected to exceed the
capabilities of multimode fiber— when exceeding the OM4 support
distance for 550 m for 10 Gbps.
10Gb/s optical fiber backbone
10 Gbps backbones utilize serial transmission with standard two-fiber
duplex cabling, in which one fiber transmits and one fiber receives. A
10 Gbps channel typically consists of backbone cables terminated (or
spliced) to LC connectors. Duplex LC patch cords are, in turn, used
to connect the backbone cabling to active networking equipment, as
shown in figure 3.
2.5/5/
10G
2.5/5/
10G
2.5/5/
10G
2005
1995
> 2015
Figure 1. Enterprise LAN cabling timeline
Optical fiber in the backbone
Backbone cabling provides interconnections between access
provider (AP) space, entrance facilities (EFs), equipment rooms (ERs),
telecommunication rooms (TRs), and telecommunication enclosures
(TEs) (See figure 2).
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LC distribution
module
Tx Tx Tx Tx
Rx Rx Rx Rx
Tx Tx Tx Tx
Rx Rx Rx Rx
10Gb/s Per Lane
10Gb/s Per Lane
25Gb/s Per Lane
25Gb/s Per Lane
40GBASE-SR4
Switching
equipment
Backbone
cable
100GBASE-SR4
Figure 4. 40GBASE-SR4 and 100GBASE-SR4 transmission schemes
Second floor
40/100G
switch
MPO cord
Duplex LC
patch cords
Switching
equipment
Second floor
12-fiber
trunk
First floor
40/100G
switch
Switching
equipment
First floor
Ground floor
Figure 3. 10 Gbps fiber backbone channel
Migrating to 40 Gbps and 100 Gbps
Unlike 10 Gbps backbones, which utilize serial transmission, current
40 Gbps and 100 Gbps multimode applications utilize a parallel
transmission scheme. 40GBASE-SR4 requires eight fibers, in which
four transmit and four receive at 10 Gbps each lane, and 100GBASESR4 requires eight fibers, in which four transmit and four receive
at 25 Gbps each lane (figure 4). In contrast to 10 Gbps backbones,
multimode backbone channels capable of supporting 40GBASE-SR4
and 100GBASE-SR4 are typically deployed with preterminated MPO
trunks, MPO pass-through panels, and MPO cords (figure 5).
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40/100G
switch
Ground floor
Figure 5. 40GBASE-SR4 and 100GBASE-SR4 channel
When migrating from 40GbE to 100GbE, 100GBASE-SR4 is
recommended, as it utilizes the same 8 fiber transmission scheme
as 40GBASE-SR4—therefore providing minimal network interruption
and the most seamless upgrade. As figure 8 illustrates, by utilizing
preterminated trunk cables in the initial 10 Gbps deployment, it is
possible to seamlessly migrate from 10 Gbps to 40 Gbps and
100 Gbps speeds by repurposing the trunk cables and replacing
the equipment or patch cords and distribution modules.
4
Existing 10G channels using MPO trunk cabling
12 duplex cords
12 duplex cords
12f each
12 duplex cords
12 duplex cords
12f each
Migration to 40GBASE-SR4 or 100GBASE-SR4
12f each
12f each
12f each
12f each
12f each
12f each
Figure 6. Migration from 10 Gbps to 100 Gbps
Backbone distances
The IEEE 802.3ba standard defines the capabilities of OM3 and OM4
fiber to support 40G and 100G Ethernet applications (Table 1). While
10GBASE-SR has a reach of 400 meters over OM4, commercially
12f each
12f to 150 meters—
available 40G and 100G systems
24f are currently limited
or 100 meters in the case of 100GBASE-SR4. 12f
However, with extended12f each
24f
reach VCSELs, it is possible to
reach 400 meters with 40 Gbps,
facilitating a seamless migration from 10G to12f
40G. It is expected
that similar extended-reach VCSELs will be available
for 100G as
12f
the market develops, but—in situations where distances beyond 150
meters are expected—installing singlemode fiber alongside multimode
will ensure that the backbone is able to accommodate speeds in
excess of 40 Gbps.
Backbone
application
12f
12f
12f
24f
24f
12f
OM3
OM4
Standard specified
max. distance
CommScope supported distance
Standard specified
max. distance
CommScope supported distance
10GBASE-SR
(850 nm)
300 meters
(984 feet)
300 meters
(980 feet)
400 meters
(1312 feet)
2-Conn 550 meters (1800 feet)
4-Conn 530 meters (1740 feet
10GBASE-LRM
(1300 nm)
220 meters
(720 feet)
220 meters
(720 feet)
220 meters
(720 feet)
220 meters (720 feet)
40GBASE-SR4
100 meters
(328 feet)
2-Conn 135 meters (440 feet)
4-Conn 125 meters (410 feet)
150 meters
(492 feet)
2-Conn 170 meters (560 feet)
2-Conn 170 meters (560 feet)
100GBASE-SR4
70 meters
2-Conn
4-Conn
85 meters (280 feet)
80 meters (260 feet)
100 meters
2-Conn 120 meters (390 feet)
4-Conn 80 meters (260 feet)
100GBASE-SR10
100 meters (328
feet)
2-Conn 135 meters (440 feet)
4-Conn 125 meters (410 feet)
150 meters
(492 feet)
2-Conn 170 meters (560 feet)
4-Conn 155 meters (510 feet)
Table 1. Multimode fiber backbone cabling distances for 10 Gbps, 40 Gbps, and 100 Gbps applications
Note 1: Standard distances are based on two connections. For channels with more connections, please refer to “SYSTIMAX Applications Performance Specifications, Volume One”.
Note 2: CommScope supported distance is applicable to installations eligible for registration for the CommScope 20 Year Extended Product Warranty and Applications Assurance
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Existing installations and support for
40Gbps and 100Gbps
Support of 40Gbps and 100Gbps over existing multimode backbones
may be accomplished with the use of an LC to MPO fanout to
connect the existing LC connectors in the installed cabling to the
MPO connector in the 40 Gbps or 100 Gbps equipment. As shown
in Figure 7, the LC cord ends connect with the LC couplers in the
shelf, while the MPO connector is inserted into the 40G or 100G
transceiver. As the transceivers are always pinned, a fanout cord with
an unpinned MPO connector is used. Consult Table 1 for maximum
distances supported, depending on the type of installed optical fiber.
LC distribution
module
40/100G
switch
pulling socks is strongly recommended when installing preterminated
cabling to protect the pre-terminated ends. Re-useable pulling socks
can be ordered to help ensure that the MPO connectors are not
damaged during installation.
The use of preterminated cabling simplifies fiber management, with
MPO to MPO connectivity throughout, and increases panel density.
This can be a significant benefit at the equipment room where multiple
40/100G links will be terminated and connected to equipment.
Conclusion
With continued growth in data rates in the horizontal driven by
applications such as 802.11ac and in-building wireless, the backbone
should be designed to accommodate speeds of 40 Gbps or 100 Gbps.
Planning for a seamless migration path ensures that the backbone will
be able to support high-capacity wireless and other high-bandwidth
applications that may emerge. Installing the proper cabling today
will extend the expected life of the structured cabling and reduce
upgrade costs over time.
Figure 7. 40/100G switch connection with array cord
Fiber management becomes more complex with this option, as
the individual LCs must be mapped to align with the transmission
schemes outlined in figure 4. This can become a significant challenge
at the equipment room where multiple 40/100G links will be
terminated and connected to equipment.
New installations and support for 40Gbps
and 100Gbps
For new installations, the use of pre-terminated MPO trunks offers
faster installation speeds, factory-assembled performance, easier
administration, and higher panel/shelf density. As shown in figure 5,
when the building backbone is deployed with preterminated MPO
trunks, MPO patch cords are used to connect the MPO connectors
in the installed cabling to the MPO connectors in the 40 Gbps or
100 Gbps equipment. As the transceivers and panel ports are always
pinned, MPO cords with unpinned MPO connectors are used.
OM3 fiber is the minimum recommendation, with OM4 fiber strongly
recommended to allow for added distance and/or connector pairs in
a link. Consult table 1 for maximum distances supported, depending
on the optical fiber type and number of connectors.
When installing preterminated cabling in the buildings, care must be
taken to ensure that the risk of damage to the preterminated ends
is minimized during installation. Installing MPO-based preterminated
fiber cabling in the riser is relatively easy if sufficient space has been
allocated and the IDFs on each floor are all located in line vertically.
However, in cases where the IDFs are not aligned and/or sufficient
space is not available in pathways, a conventional approach as
described for existing installations may be appropriate. The use of
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Everyone communicates. It’s the essence of the human
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WP-109423.1-EN (04/17)