25Jun12 System Design Comparisons v2.0

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If a System Operator is considering a new HFC network, or a network upgrade, or rebuild, the total cost of the project must be estimated.

This can be done by designing a few small, selected areas of the network; perhaps 1,000 or 2,000 homes-passed. The costs of these small areas can then be extrapolated to the entire network.

If the area covered by the entire network has a uniform population density; if the type of housing (single-family, multi-family, etc.) is the same across the entire network, and if the street patterns are the same, then a singleSample Design area can be selected. But if these characteristics vary significantly from place to place, then two or three Sample Design areas must be selected, to represent all the different population densities, types of dwelling, and street patterns.



In this example, we examine a ‘network upgrade’.

The existing system has a downstream frequency limit of 750 MHz, and an upstream frequency limit of 42 MHz. The customer wants to upgrade the network so that the downstream frequency range is 105 MHz to 1 GHz, and the upstream frequency range is 5 to 85 MHz. (That is, the latest HFC technology).

After an analysis of the bandwidth requirements, based on the volume of Internet services, VoD, etc., it was found that a Serving Area of 500 homes-passed per Optical Node will be required. However, the traffic is expected to increase, so that a Serving Area of 125 homes-passed will be required in the near future. Therefore the new Optical Nodes must be segmentable, and the upgrade architecture must allow this segmentation must be possible with minimum cost and minimum disruption of customer services.

We will also examine ‘Node Only’ architectures, which will reduce the Serving Area even further.



The existing network is approximately 16 years old. It was designed primarily for Downstream transmission; there are no specifications for Upstream RF signal levels.

The RF passive devices and the subscriber taps are capable of carrying signals at 1 GHz, so it may not be necessary to replace all these devices.



Here are the characteristics of the two areas that are served by the existing Optical Nodes.

Each node is connected to approximately 500 homes.

This is a ‘node-plus-three’ architecture, so there are many RF amplifiers associated with each Optical Node.

(NOTE: these are Suburban areas, and the population density is low).



In this option (Architecture ‘1’), the objective is to split each existing node area into four smaller segments, each containing approximately 125 homes-passed. This is done by removing the existing optical node, and replacing it with a fully-segmented GS7000 node. Each RF port of this new node is therefore connected to ~125 homes-passed, and so it effectively becomes four independent nodes in one housing.

This is referred to as a ‘drop-in’ segmentation.

Also, the existing RF amplifiers are replaced with 1 GHz ‘GainMaker’ amplifiers, with a 85/105 MHz frequency split.



When the new optical nodes are installed, there will be an average of 130 homes-passed per segment in Node ‘50’, and 133 homes-passed per segment in Node ‘51’.

A detailed description of the number of homes-passed per RF port on the new optical nodes is shown. Note that the ‘balance’ of the segments is not perfect; for example, in Node ‘50’ one segment has 184 h-p, and another has only 93. This imbalance is unavoidable when a simple ‘drop-in’ segmentation is performed.



The Sample Design for Architecture ‘1’ is shown in this diagram of the upgraded Node ‘50’.

There are 21 RF amplifiers. This number has not increased, because we have replaced the existing 750 MHz amplifiers with the new 1 GHz amplifiers. The new amplifiers have more gain, to compensate for the increased attenuation at 1 GHz.

Now there are four segmented nodes in place of one node.

We must assume that there is a sufficient number of fibres in the cable; if not, we must use an optical multiplexing system for both the Downstream and Upstream traffic.

(In this example, we need 4 fibres for Downstream traffic, and 4 fibres for Upstream traffic. If eight fibres are not available, it is possible to use the Cisco ‘MultiWave’ system for the Downstream traffic, and CWDM or DWDM for the Upstream traffic. This will reduce the number of required fibres to two).




There are 25 RF amplifiers. This number has not increased, because we have replaced the existing 750 MHz amplifiers with the new 1 GHz amplifiers. The new amplifiers have more gain, to compensate for the increased attenuation at 1 GHz.

Now there are four segmented nodes in place of one node.

Again, we must assume that there enough fibres available to support the Downstream and Upstream optical connections. If not, we must use optical multiplexing, as shown in the previous slide.



The GS7000 node is recommended for these upgrades.

There are several types of optical node in the Cisco product familiy, but the GS7000 is the most flexible. It has the capability of segmenting both the Downstream and Upstream paths into four segments, so that each RF port on the node can have its own optical receiver and transmitter.

Another attractive feature of the GS7000 is that it is based on the design of the GainMaker amplifiers. This means that the pads and equalizers are the same size and shape.

Customers can choose either one or two power supplies, and an optional Transponder is also available. This module allows the node to be monitored by an Element Management system at the Headend.



If the number of fibres at an existing Optical Node is limited, we can use optical multiplexing in both the Downstream and the Upstream signal paths. For short distances (less than 25 km), we can use the Cisco 1310 nm ‘MultiWave’ system; up to 6 wavelengths can be carried on a single fibre, and each wavelength can carry a full spectrum of analog and digital traffic. (For example, 78 analog video signals and 75 QAM signals).

In the Upstream signal path, we have several options. We can use CWDM (the least expensive option) to multiplex the signals from up to 8 Optical Nodes on a single fibre.

We can also offer 40 wavelengths using DWDM multiplexing.



NOTE: the prices in this table are typical Selling Prices, and should not be regarded as a firm price Proposal.

The Cisco equipment includes Optical Nodes, GainMaker amplifiers and optical transmitters and receivers.

The ‘Other vendor’ equipment includes coaxial connectors, housing-to-housing connectors, and splice enclosures.

No new taps and passives, or fibre or coaxial cable are required. In other words, this is a true ‘drop-in’ upgrade.



In this option (Architecture ‘2’), the objective is, again, to split each existing node area into smaller segments, but with a better ‘balance’ between the segments. This is done by removing the existing optical node, and replacing it with a fully-segmented GS7000 node. In addition, one of the RF amplifiers is converted to a non-segmented optical node, and new fibre cable is installed to connect this new node to the existing splice enclosure. Also, all other existing RF amplifiers are replaced with 1 GHz ‘GainMaker’ amplifiers, with a 85/105 MHz frequency split.



When the new optical nodes are installed, there will be an average of 99.4 homes-passed per segment in Node ‘50’, and 101.7 homes-passed per segment in Node ‘51’.

A detailed description of the number of homes-passed per RF port on the new optical nodes is shown. Note that the ‘balance’ of the segments has now neen improved: the largest segment in Node ’50’ contains 130 homes-passed, and the smallets segment has 92 homes-passed. Similarly, in Node ’51’, the largest segment has 127 homes-passed, and the smallest has 81 homes-passed.




There are 20 RF amplifiers; in the existing network there are 21. This is because the upgrade involves the conversion of one amplifier to a Node (referred to as Node ‘50b’).

Now there are five segments in this area.





There are 24 RF amplifiers; in the existing network there are 25. This is because the upgrade involves the conversion of one amplifier to a Node (referred to as Node ‘51b’).

Now there are five segments in this area.




This upgrade scenario will be very simple if the existing RF amplifiers are Cisco GainMaker products.

A GainMaker amplifier can be converted to an optical node by removing half of the housing, and replacing it with a module that contains the optical receiver and transmitters, and power supply.

If the existing HFC network contains older Cisco equipment (Scientific-Atlanta equipment), then it will be necessary to replace the complete amplifier. BUT the mechanical dimensions of our amplifiers and nodes have not changed for many years, so it may be possible to replace a 750 MHz amplifier with an optical node, without using ‘extension connectors’, and without re-splicing the coaxial cable.





The ‘Other vendor’ equipment includes coaxial connectors, housing-to-housing connectors, and splice enclosures.

No new taps and passives are required. New fibre cable is required between the existing splice enclosure and the new node: 160m is needed in Node ‘50’ and 430m in Node ‘51’. A 6-count fibre cable is recommended in both cases.



In this option (Architecture ‘3’), the existing node and all active RF devices (amplifiers) are removed, and replaced by low-cost nodes; new fibre cable must be installed to each of these new nodes.

This greatly reduced the number of homes-passed per node, which means that the bandwidth available to each subscriber is increased significantly, and high-speed data (DOCSIS), Video on Demand (VoD) and high-definition digital video services can all be expanded.

Also, there will be some improvement in signal quality, because RF amplifiers are eliminated.

In most cases, there will not be a sufficient number of fibres available at the existing splice enclosure for separate connections of all the new nodes to the Headend, and possibly a DWDM multiplexing system will be required in both the Downstream and Upstream signal paths.



The GainStar nodes are recommended for ‘node only’ architectures, because of their low cost. They do not have all the features of the GS7000 and the GainMaker nodes, but these features, such as segmentability, are not required when the node is connected to a small number of subscribers. Also, two RF ports are sufficient in most cases. (NOTE: the GainStar node in this picture has four RF ports, but the two additional ports are activated by means of internal splitters or couplers).



When all the active devices are replaced by low-cost GainStar nodes, there will be an average of 23.6 homes-passed per node in ‘50’, and 20.4 in ‘51’.

Note that the numbers of power supplies have not changed.




The existing network has 21 RF amplifiers and one node. In this upgrade scenario, there will be 22 nodes and no RF amplifiers.

Now there are effectively twenty-two segments in this area.

We assume that DWDM optical multiplexing must be used for the Downstream traffic from the Headend. In the Upstream path, we can again use DWDM, but a lower-cost option may be CWDM, using three fibres for transmission. (CWDM multiplexers are available with eight wavelengths, so to accommodate 22 wavelengths, we must use three 8-way multiplexers).





Now there are effectively twenty-six segments in this area.

We assume that DWDM optical multiplexing must be used for the Downstream traffic from the Headend. In the Upstream path, we can again use DWDM, but a lower-cost option may be CWDM, using four fibres for transmission. (CWDM multiplexers are available with eight wavelengths, so to accommodate 26 wavelengths, we must use four 8-way multiplexers).




The Cisco equipment includes Optical Nodes, optical transmitters and receivers.

The ‘Other vendor’ equipment includes fibre cable and splice enclosures.

No new taps and passives are required. A large amount of new fibre cable is required between the existing splice enclosure and the new nodes: 5.4 km is needed in Node ‘50’ and 5.28 km in Node ‘51’. A 6-count fibre cable (at each node) is recommended in both cases.



In this option (Architecture ‘4’), the existing node and all active RF devices (amplifiers) are removed, and new, high-output (GainMaker) nodes are installed; new fibre cable must be installed to each of these new nodes.

The numberof homes-passed per node is higher than that in Archiecture ‘3’, but when we compare the ‘drop-in’ strategies of Architectures ‘1’ and ‘2’ with this option, the bandwidth available to each subscriber is still increased significantly, and high-speed data (DOCSIS), Video on Demand (VoD) and high-definition digital video services can all be expanded.

Also, there will be some improvement in signal quality, because RF amplifiers are eliminated.

In most cases, there will not be a sufficient number of fibres available at the existing splice enclosure for separate connections of all the new nodes to the Headend, and possibly a DWDM multiplexing system will be required in both the Downstream and Upstream signal paths.



In the ‘optimized’ node-only architecture, all the RF amplifiers are removed, and ‘high-output’ GainMaker nodes are installed at strategic locations. These nodes can operate with an RF output level of 56 dBmV (at 1 GHz), which allows them to serve a large number of subscribers. (An average of 66.5, in this scenario). A mixture of 2-, 3- and 4-output GainMaker nodes will be required.

Also note that the number of power supplies is reduced from two to one, in both of the Sample Design areas.



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Now there are effectively eight segments in this area.

We assume that DWDM optical multiplexing must be used for the Downstream traffic from the Headend. In the Upstream path, we can again use DWDM, but a lower-cost option may be CWDM, using one fibre for transmission.





The ‘Other vendor’ equipment includes coaxial connectors, housing-to-housing connectors, fibre cable and splice enclosures.

No new taps and passives are required. A large amount of new fibre cable is required between the existing splice enclosure and the new nodes: 3.04 km is needed in Node ‘50’ and 3.03 km in Node ‘51’. A 6-count fibre cable (at each node) is recommended in both cases.

New coaxial cable is also needed in this scenario. Node ‘50’ requires 1,003m of 0.650-inch cable, and Node ‘51’ requires 729m.



In this final slide, we see the costs of each of the three Architectures.

Clearly, the ‘simple segmentation’ is the least expensive. This is because all the HFC plan, including the coaxial and fibre cable, remains unchanged, and only the existing node is replaced by a 4-way segmented node.

The most expensive option is the ‘Node Only’ architecture, because all the RF amplifiers are converted to nodes. Although the nodes are low-cost, a large amount of additional optical equipment is required at the Headend, and also a large amount of new fibre cable. The labo costs are also high.

25Jun12 System Design Comparisons v2.0

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