Application Report
Interoperability of CommScope MicroNodes
and Legacy NIUs
Background
CommScope’s BrightPath® product was one of the first
entries into what was to become known as the Radio Frequency over Glass (RFoG) product space. The 2000 series
Network Interface Unit (NIU) was released to the market
in 2007 and at the time, there were no industry accepted
standards in place to define the functions and characteristics
that should be considered. CommScope relied on decades
of cable plant operations experience, input from customers
and best engineering practices to develop the initial product.
CommScope was also heavily involved in the development of the RFoG standard that was released by the SCTE
in 2010 (ANSI/SCTE 174 2010). This standard defined a
fiber-to-the-home system optimized for compatibility with hybrid fiber-coax (HFC) plant, using the same end equipment
at both the home and at the headend or hub. A key element
in the standard is the definition of what is referred to as the
RFoG Optical Networking Unit or R-ONU. CommScope
released an SCTE 174 based product in 2010 with a trade
name of BOS-MN-1302 or 1302 series MicroNode.
Prior to the release of the SCTE based product, CommScope had
many customers with substantial deployments of the pre-standard
2000 series NIUs. With the release of the BOS-MN-1302 product, CommScope discontinued the 2000 series NIU. Although the
2000 series NIU and the 1302 MicroNodes are not equivalents
with minimal planning and basic adjustments, they can operate
properly on the same optical network and provide excellent performance while doing so.
Operational Considerations
As in any communications network, the RFoG network must be
properly set up in order to achieve maximum performance.
Regardless of whether the deployment is node based or a direct
feed, care must be taken during the customer premise installation
to ensure best performance. CommScope recommends that the
customer premise installation conform as closely as possible to the
diagrams below.
Customer Premise Network
1)
Customer Premise Network
2)
A key takeaway from the diagram is that the RF feed from the
MN always goes through:
1) Low count splitter with one leg of the splitter feeding the cable
modem and the other leg feeding an additional splitter for
video applications throughout the customer premise, or
2) A multiport directional coupler (MDC) with the through port
feeding the cable modem and the tapped legs feeding the
video applications throughout the customer premise.
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This is extremely important in an RFoG network because we
want to have consistent modem transmit levels throughout the
deployment. This allows adjustments to the transmit levels to be
made on a node or fiber basis through attenuation in the return
path versus having to address each cable modem individually.
If the attenuation between the MicroNode and the cable modem is not consistent, it will be very difficult to tune the network
for optimal performance.
Differences between the NIU and MN
There are some fundamental differences in the manner in which
the NIU and the MicroNode operate. Some of the key parameters are shown in the table below:
Parameter
2000 Series NIU
MicroNode
0 to -5 dBm
0 to -6 dBm
14 dBmV @ Channel 2
17 dBmV @ 550MHz
US RF
Input Range
30 to 55 dBmV
20 to 45 dBmV
RF US Gain
0 dB
+15 dB
DS Optical
Input Range
RF Output
Optimizing the Network
If it becomes necessary to deploy a
MicroNode on a network already
populated with NIUs or if a MicroNode
is used in a new installation where NIUs
are already being used on a network,
there are some basic steps that can be
taken to ensure that all modems on the
network transmit at the same level and at
a level that optimizes performance. The
simplest and most consistent method is to
insert reverse path attenuation between
the MicroNode and the cable modem in
order to raise the cable modem’s transmit
level to a level that is equal to that of
cable modems subtending the NIU.
In the network setup illustrated below,
the cable modems are transmitting at
the same level and the same power is
being delivered to the return receiver.
The reverse path attenuation applied
to the premise network subtending the
MicroNode is compensated by the gain
function in the MicroNode.
It is obvious that the 15 dB RF upstream gain in the MicroNode
will have an impact on the upstream signal. When inserting
a MicroNode into a network that is populated with NIUs or
replacing an NIU with a MicroNode, we must consider how the
upstream RF gain will affect the performance of the subtending
cable modem. Assuming that the customer premise network is
the same, the cable modem will transmit at a 15 dB lower level
with the MicroNode than it did with the NIU due to the upstream
RF gain.
In a scenario where there are modems subtending the NIU and
transmitting in the 35 to 40 dBmV range, replacement of the
NIU with a MicroNode will cause the modems to transmit in
the 20 to 25 dBmV range. While this is within the standards
specifications for upstream transmission, CommScope has observed that some cable modems tend to either perform poorly or
sporadically at these lower output levels.
Customer Premise Network
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This scenario was tested in CommScope’s lab and has been
successfully deployed by customers. In the lab setup, a 25 dB link
budget on a direct feed was created. The return network was
configured so the cable modem subtending the NIU was transmitting upstream at 50 dBmV. A 1302 MicroNode was placed on
the same network with a 12 dB reverse window attenuator between the cable modem and the MicroNode. The added attenuation caused the cable modem subtending the MicroNode to also
transmit at approximately 50 dBmV. The NPR curve below shows
that the performance for both the NIU and the 1302 MicroNode
is approximately the same in this scenario.
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Visit our Website or contact your local CommScope
representative for more information.
© 2012 CommScope, Inc. All rights reserved.
All trademarks identified by ® or ™ are registered trademarks
or trademarks, respectively, of CommScope, Inc.
This document is for planning purposes only and is not intended to modify or supplement any specifications or warranties
relating to CommScope products or services.
TP-106277-EN • 10.12
Conclusion
It is possible to operate CommScope’s legacy 2000 series
NIU and the newer 1xxx series MicroNodes on the same optical network and achieve very satisfactory performance from
both units. Care must be taken to consistently install and setup
the customer premise, but this should be standard practice for
any RFoG network installation.