We’ve covered most of the types of NBN Node, but the “Micronode” isn’t something we’ve looked at. Micronodes are “satellites” that hang off a larger Nokia ISAM and act as NBN FTTN DSLAMs.
In NBN documentation these are referred to as “Compact Sealed DSLAMs” or CSDs, and in Nokia/Alcatel documentation these are called Sealed Expansion Modules (SEMs) – Regardless of what you call them, they act as 48 port VDSL capable DSLAMs like rest of the Nokia / Alcatel ISAM family that are used for FTTN.
They are similar in concept to the NBN FTTC program, except these units are not reverse powered, and they have a higher subscriber count.
They’re housed in the green cabinets that were used for the HFC / Pay TV networks installed in some locations underground.
The CSD are a Nokia 7367 ISAM SX-48V (White box with the heat sink on the left of the photo below) which is connected directly back to the nearest exchange.
There is also an internal PSU with batteries powered from the incoming unmetered AC supply and a PSU is supplied by Alpha technologies in the photo on the right (With the spider).
On the flip side of the unit is where the copper pairs come in, and the DSLAM X-Pairs go out, and a small fibre splice tray.
At long last, more and more Australians are going to have access to fibre based access to the NBN, and this seemed like as good an excuse than any to take a deep dive into how NBN’s GPON based fibre services are delivered to homes.
Let’s start in your local exchange where you’ll likely find a Nokia (Well, probably Alcatel-Lucent branded) 7210 SAS-R access aggregation switch, which is where NBN’s transmission network ends, and the access network begins.
It in turn spits out a 10 gig interface to feed the Optical Line Terminal (OLT), which provides the GPON services, each port on the OLT is split out and can feed 32 subscribers.
In NBN’s case, Nokia (Alcatel-Lucent) 7302, and rather than calling it an OLT, they call it a “FAN” or “Fibre Access Node” – Seemingly because they like the word node.
Each of the Nokia 7302s has at least one NGLT-A line card, which has 8 GPON ports. Each of the 8 ports on these cards can service 32 customers, and is fed by 2x 10Gbps uplinks to two 7210 SAS-R aggregation switches.
The chassis supports up to 16 cards, 8 ports each, 32 subs per port, giving us 4096 subscribers per FAN.
In some areas, FANs/OLTs aren’t located in an exchange but rather in a street cabinet, called a Temporary Fibre Access Node – Although it seems they’re very permanent.
In reality, each port on the OLT/FAN goes out Distribution Fibre Network or DFN which links the ports on the OLTs to a distribution cabinet in the street, known as as a Fibre Distribution Hub, or FDH.
If you look in FTTH areas, you’ll see the FDH cabinets. The FDH is essentially a roadside optical distribution frame, used to cross connect cables from the Distribution Fibre Network (DFN) to the Local Fibre Network (LFN), and in a way, you can think of it as the GPON equivalent of a pillar, except this is where we have our optical splitters.
Remember when we were talking about the FAN/OLT how one port could serve 32 subscribers? We do that with a splitter, that takes one fibre from the DFN that runs to the FAN, and gives us 32 fibres we can could connect to an ONT onto to get service.
Inside the FDH showing the Distribution Fibre Network (DFN) connecting to the optical splitters belowDistribution Fibre Network with up to 576 fibres running out and down streets, with parking below
The FDH cabinets are made by Corning (OptiTect 576 fibre pad mounted cabinets) and you can see in the top right the Aqua cables go to the Distribution Fibre Network, and hanging below it on the right are the optical splitters themselves, which split the one fibre to the FAN into 32 fibres each on SC connectors.
These are then patched to the Local Fibre Network on the left hand side of the cabinet, where there’s up to 576 ports running across the suburb, and a “Parking” panel at the bottom where the unused ports from the splitter can be left until you patch the to the DFN ports above.
The FDH cabinets also offer “passthrough” allowing a fibre to from the FAN to be patched through to the DFN without passing through the GPON splitter, although I’m not clear if NBN uses this capability to deliver the NBN Business services.
But having each port in the FDH going to one home would be too simple; you’d have to bring 576 individually sheathed cables to the FDH and you’d lose too much flexibility in how the cable plant can be structured, so instead we’ve got a few more joints to go before we make it to your house.
From the FDH cabinet we go out into the Local Fibre Network, but NBN has two variants of LFN – LFN and Skinny LFN. The traditional LFN uses high-density ribbon fibres, which offer a higher fibre count but is a bit tricker to splice/work with. The Skinny LFN uses lower fibre count cables with stranded fibres, and is the current preferred option.
The original LFN cables are ribbon fibres and range from 72 to 288 fibre counts, but I believe 144 is the most common.
These LFN cables run down streets and close to homes, but not directly to lead in cables and customer houses.
These run to “Transition Closures” (Older NBN) or “Flexibility Joint Locations” (FJLs – Newer NBN)
While researching this I saw references to “Breakout Joint Locations” (BJLs) which are used in FTTC deployments, and are a Tenio B6 enclosure for 2x 12 Fibers and 4x 1 Fibers with a 1×4 splitter.
The FJLs are TE Systems’ (Now Commscope) Tenio range of fibre splice closures, and they’re use to splice the high fibre count cable from from the FDH cabinets into smaller 12 fibre count cables that run to multiple “Splitter Multi Ports” or “SMPs” in pits outside houses, and can contain splitters factory installed.
Sealed NBN FJLOpen NBN FJLReassembled NBN FJLFJL in situ in pitNeat open FJL
The splitters, referred to as “Multiports” or “SMPs” are Corning’s OptiSheath MultiPort Terminals, and they’re designed and laid out in such a way that the tech can activate a service, without needing to use a fusion splicer.
Due to the difficulty/cost in splicing fibre in pits for a service activation, NBNco opted to go from the FJL to the SMPs, where a field tech can just screw in a weatherproof fibre connector lead in to the customer’s premises.
During installation / activation callouts, the tech is assigned an SMP in the pit near the customer’s house, and a port on it. This in turn goes to the FJL and onto FDH cabinet as we just covered, but that patching/splicing for that is already done, so the tech doesn’t need to worry about that.
SMP in pitCorning OptiSheath Multiport SplitterSMP in a pit
The tech just plugs in a pre-terminated lead in cable with a weatherproof fibre end, and screws it into the allocated port on the SMP, then hauls the other end of the lead in cable to the Premises Connection Device (Made by Madison or Tyco), located on the wall of the customer’s house.
TC000006252
The customer end of the lead in cable may be a pre terminated SC connector, or may get mechanically spliced onto a premade SC pigtail. In either case, they both terminate onto an SC male connector, which goes into an SC-SC female coupler inside the PCD.
Next is the customer’s internal wiring, again, preterm cable is used, to run between the PCD and the First Fibre Wall Outlet inside the house. This preterm cable join the lead in cable inside the PCD on the SC-SC female coupler, to join to the lead in.
Inside the house we have the “Network Termination Device” (NTD), which is a GPON ONT, is where the fibre from the street terminates and is turned into an Ethernet handoff to the customer. NBN has been through a few models of NTD, but the majority support 2x ATA ports for analog phones, and the option for an external battery backup unit to keep the device powered if mains power is lost.
Phew! That’s what I’ve been able to piece together from publicly available documentation, some of this may be out of date, and I can see there’s been several revisions to the LFN / DFN architectures over the years, if there’s anything I have incorrect here, please let me know!
I am connected on a VDSL line, not by choice, but here we are. DSL is many things, but consistent it not one of them, so I thought it’d be interesting to graph out the SNR and the line rate of the connection.
This is an NBN FTTN circuit, I run Mikrotiks for the routing, but I have a Draytek Vigor 130 that acts as a dumb modem and connects to the Tik.
Draytek exposes this info via SNMP, but the OIDs / MIBs are not part of the standard Prometheus snmp_exporter, so I’ve added them into snmp_exporter.yaml and restarted the snmp_exporter service.
Note: All information contained here is sourced from: Photos provided by NBNco’s press pages, Googling part numbers from these photos, and public costing information.
This post covers the specifics and capabilities of NBNco’s FTTN solution, and is the result of some internet sleuthing.
If some of the info in here is now out of date, I’d love to know, let me know in the comments or drop me an email and I’ll update it.
FTTN in Numbers
A total of 24,544 nodes have been deployed upon completion of roll out. Each node is provisioned with 384 subscriber ports.
The hardware has 10Gbps shared between the 384 subscriber lines, equating to 208Mbps per subscriber.
Construction costs were $2.311 billion and hardware costs were $1.513 billion,
For the hardware this equates to $61,644 per node or $160 per subscriber line connected (each node is provisioned with 384 ports)
Full cost for node including hardware, construction and provisioning is $244,150 per node, which is $635 per port.
To operate the FTTN infrastructure costs $709 million per year (Made up of costs such as power, equipment servicing and spares). This equates to $28k per node per annum, or $75 per subscriber. (This does not take into account other costs such as access to the copper, transmission network, etc, just the costs to have the unit powered on the footpath.)
Overview
Inside the FTTN cabinets is a Alcatel Lucent (now Nokia) ISAM 7330 cabinet mounted on it’s side,
On the inside left of the door is a optic fibre tray where the transmission links come into the cabinet,
On the extreme left is a custom panel. It contains I/Os that are fed to the 7330, such as door open sensor, battery monitoring, AC power in, SPD and breaker.
Connection to subscriber lines happens on a frame at the end of the cabinet.
Alcatel Lucent ISAM 7330 FTTN
NBN co’s nodes are made up of Alcatel Lucent (Now Nokia) ISAM (Intelligent Services Access Manager) 7330 FTTN rack mounted it’s side.
Slot
Type
Function
1
GFC (General Facilities Card)
Power and alarm management
2
NT Slot (NANT-E Card)
Main processing and transmission
3
NTIO Slot (NDPS-C Card)
VDSL vectoring number-crunching
4
NT Slot (Free)
Optional (Unused) backup Main processing and transmission
5-12
LT (NDLT-F)
48 Port VDSL Subscriber DSLAM Interfaces
Slot numbering is just counting L to R, ALU documentation has different numbering
First up is the GFC (General Facilities Card) which handles alarm input / output, and power distribution. This connects to the custom IO panel on the far left of the cabinet, meaning the on-board IO ports aren’t all populated as it’s handled by the IO panel. (More on that later)
Next up is the first NT slot, there are two on the 7330, but in NBN’s case, only one is used; the second can be used for redundancy if one of the cards were to fail, but it seems this option has not been selected. In the first and only populated NT slot is an NANT-E Card (Combined NT Unit E) which handles transmission and main processing.
All the ISAM NANT cards support support RIPv2! But only the NANT-E card also supports BGP – Interestingly they don’t have BGP on all the NANT cards?
To the right of that is the NTIO slot, which has a NDPS-C card, which handles the vector processing for VDSL.
Brief overview of Vectoring: By adding vectoring to DSL signals allows noise on subscriber loops to be modeled, and then cancelled out with an integrated anti-phase signal matching that of the noise.
The vectoring in VDSL relies on pretty complex number crunching as the DSLAM has to constantly process the vectoring coefficients which are different for each line and can change based on the conditions of the subscriber loop etc. To do this the NDPS-C has two roles; The NDPS-C’s Vectoring Control Entity performs non-real time calculations of vectoring coefficients and handles joining and leaving of vectored VDSL2 lines. While the NDPS-C’s Vectoring Processor performs the real time matrix calculations based on crosstalk correction samples for the VDSL symbols collected from the subscriber lines. The NDPS-C has a Twinax connection to every second LT Card.
After the NTIO slot is the unused NT slot.
Finally we have the 8 LT slots for line cards, which for FTTN is using the NDLT-F are 48 port line cards.
The 8 card slots allows 384 subscriber lines per node.
These are the cards which the actual subscriber lines ultimately connect to. With 10Gbps available from the NT to the LTs, means each LT card with 48 subs so 208 Mbps per subscriber max theoretical throughput.
POTS overlay is supported, this allowed VF services coexisted on the same copper during the rollout. M / X pairs are no longer added inline on new connections. (More on that on cabling).
Power & Environment
The 7330 has a 40 amp draw at -48v would mean the unit consumes 1920w
The -48v supply is provided by 2x Eltek Flatpack2 rectifiers, each providing 1Kw each.
These can be configured to provide 1Kw with redundancy to protect against the failure of one of the Flatpack2 units, or 2Kw with no redundancy, which is what is used here.
On the extreme left is a custom panel. It contains alarm I/Os that are fed to the 7330, such as door open sensor, battery monitoring, etc.
It also is the input for AC power in, surge protection device and breakers.
I did have some additional information on the batteries used and the power calculations, however NBNco’s security team have asked that this be removed.
Cabling
Incoming transmission fiber comes in on NBNco’s green ribbon fibre, which terminates on a break out tray on the left hand side wall of the cabinet. Spliced inside the tray is a duplex LC pigtail for connecting the SMF to the 7330. I don’t have the specifics on the optics used.
Subscriber lines come in via an IDC distribution frame (Quante IDS) on the right hand side end of the cabinet, accessed through a seperate door.
This frame is referred to as the CCF – Cross Connect Frame.
There are two sets of blocks on the CCF, termination of ‘X’ and ‘C’ Pairs.
‘X’ Pairs are the VF Pairs (PSTN lines) connecting to the pillar where they are jumpered back to the ‘M’ pairs back to the serving exchange,
‘C’ Pairs are the pairs containing combined VDSL & VF services to to the pillar where they are jumpered to the ‘O’ pairs which run out to the customer’s premises,
I’m a bit of a radio nerd & I’ve worked Satellites before, so the Skymuster / LTSS program had me curious. So here’s some nitty-gritty details on NBNCo’s Skymuster Satellite service.
The Payload
NBNco called the LTSS (Long Term Satellite service) but before launch they re-branded as “Skymuster”.
NBNco provided an Interim service called ISS (Interim Satellite Service). before the launch. IPSTAR satellite (Formerly ABG) and Optus services delivered this. Both of these had limited bandwidth and has since been largely replaced by the Skymuster / LTSS.
NBNCo contracted Space Systems / Loral, a US based satellite manufacturer to design and build the payloads. It’s based on the SSL 1300 platform.
When deployed, the payload itself measures 26 metres long, 9 metres tall and 12 metres wide, and weighs in at 6400Kg. Before deployment, in the satellite’s compressed form it fits within a 5-meter launch-vehicle fairing.
Communication to earth is via Ka-band frequencies which allows for greater density of spot beams and frequency reuse. However, capacity improvement through higher frequencies does come with some tradeoffs. Ka-band frequencies, are more susceptible to weather related conditions compared to Ku-band frequencies. Directional accuracy becomes way more important when aligning the customer dishes in Ka band also.
SSL provided image of SL-1300
Direction
Min Freq
Max Freq
Earth to Satellite
27Ghz
31Ghz
Satellite to Earth
17.7Ghz
22Ghz
These emissions are within the range of the higher end software defined radio receivers. I’m curious to see what’s being transmitted, but that’s a topic for another day.
The downlink uses RH and LH circular polarisation.
The Journey
SSL assembled the satelite in California.
SSL staff packed it into a crate and loaded into the belly of an Antinov An-124 which is flown to the launch site.
There are two Skymuster Satellites, NBN-Co 1A & 1B. 1B provides infill / capacity layer for 1A but both are identical. If the 1A satellite was lost during launch / deployment, 1B could be sent up in it’s place. This is still a real risk when launching anything.
NBN-Co 1A was the first launched, riding on a Ariane-5ECA from Guiana Space Centre in French Guiana, South America. 1A launched on 30.09.2015 and 1B launched 05.10.2016 in the same configuration.
After launch to a transit orbit, the satellites had to navigate up into a geostationary orbit at ~36,000Km. This was done using it’s 4 × SPT-100 plasma thrusters, which are exactly as cool as they sound. The final navigation process took up 40% of the fuel in the satellite. Fuel is the determining factor for the expected ~15 year lifetime of the two satellites.
SPT-100 – Source: NASA
Once in final position SSL performed 2 months worth of tests referred to as “In Orbit Testing”. SSL then handed over operational Telemetry, Tracking and Command (TT&C) to Optus Satellite (Singtel). Optus are tasked with keeping it in it’s current position.
Customer Hardware
Ericsson manage the installation, and subcontract to Hills and Skybridge for the actual work.
Out Door Unit (ODU)
There are currently 3 Satellite Antenna options that are available for installation, 80cm, 1.2m & 1.8m.
NBNco’s Test Setup
Narrower Ka-Band signals drops off more rapidly than Ku-Band signals. This means that aligning the Ka-Band antenna within the degrees of usable Azimuth within the Line of Sight maximises the antenna gain.
Required accuracy for each of the antennas:
80 cm: 1.4 degrees,
120 cm: 1.0 degrees
180 cm: 0.7 degrees
The below graph shows being off by 1 degree from the required accuracy, leads to -30dB drop. This translates to a power ratio of 1000, or 1/1000 of the power if correctly aligned.
The alignment process is done by the installer pointing the dish in the correct azimuth / elevation. This is based on compass / inclinometer readings, or smart phone apps. Once a rough alignment has been set, a tone-generator on the TIRA is used to align the dish.
This process requires a 16 digit installation key.
The key containing the frequency used in the installation, beam Assignment & TRIA Polarisation (The 6w version has automatic (Polarisation).
That’s entered into the installation setup page at:
The TRIA is the equivalent of a feed horn, an all in one Tx/Rx assembly. They are available in 3w and 6w variants, based on the estimated signal levels of the installation location. That’s determined by factors like high rain areas or if the subscriber is on the edge of a beam.
3W Version
The 6W version has an extra F-Connector for the required DC power injection. The 6w version also has a two F-Connector gang-plate / wallplate when installed for the second RG6 run to power it.
Interestingly there’s a minimum length of cable run (8m) specified for these installations. Anything less than 8m leads to lower resistance and possible overheating.
There is a minimum length of 8m for the cable run this is very important as it provides the right amount of cable resistance so the modem does not get hot and over heat. Max cable run is 50m.
Configuration
Transparent Performance Enhancing Proxy (TPEP)
TPEP aka Web Acceleration, is a service offered by NBNco to spoof TCP replies, to make the handshake more efficient. It can, unsurprisingly, lead to headaches accessing services, particularly those that employ TLS.
The installer key sets the beam, and his can be remotely changed by NBNco MAC / NOC team.
BIRRAUS have a good article explaining the spot beams available.
Educational Port
Like the other NBNco NTDs, there are multiple UNI-D ports available on the Skymuster modem allowing segregation of services.
One option that seems to be gaining traction is a dedicated port on the modem for educational use, on one of the UNI-D ports on the modem.
Educational Ports are configured to allow access for remote / distance education students.
The local state government sets pricing, speeds and data usages.
Ground Stations
There are 9 active and one standby ground stations, geographically spread across Australia, with a standby in Wolumna, NSW. The standby is capable of assuming control for any of the other ground stations.
ViaSat built the equipment and services different spot beams.
Again, BIRRAUS have this covered in their article, but here’s an extract they’ve made listing the ground stations and beams serviced.
Wolumla ground station
Future
Solar Transit
Solar transits happen twice yearly when the satellite is aligned directly between the sun and Australia.
The immense solar radiation from the sun overloads the transceivers on the ground, as they’re positioned at the satelite, with the sun behind it overloading the signals.
This lasts for about 6 minutes twice yearly, and affects different ground stations and each of the satellites at different times.
Copper Cutoff
Currently the copper decommissioning does not apply to Skymuster services. This means customers with a copper POTS line, can keep it indefinitely.
This has lead to headaches with incumbent providers who had intended to decommission / sell off remote exchanges, but will be required under Universal Service Obligation to keep them active.
3rd Satellite
Due to unexpectedly large uptake of Skymuster services, NBNco had floated the possibility of launching a 3rd Satelite in 2020:
Scenario 3: Third satellite – This scenario assumes that NBN Co constructs and launches a third satellite at the end of CY20. This mitigates the need to build some fixed wireless base stations and FTTN distribution areas. The capacity of this satellite will only be partially required to meet NBN Co’s needs
Scenario 4: Third satellite in partnership – This scenario mirrors Scenario 3, but assumes that NBN Co enters into a partnership with an external party to access only the required capacity on a third satellite rather than building and owning it outright.
The NBNco launched a fleet of “Road Muster” 4WDs for promotion of the services. They drive from town to town, spruiking the benefits of Skymuster.
On the roof of the 4WD is a Satellite ODU, which seems to be self / remote positioning.
Online sleuthing reveals it’s a EXPLORER 8120 manufactured by Cobham. It featuring auto-acquire, drive-away antenna system using Dynamic Pointing Correction technology. At $32k USD, it’s rather pricey, and outside the range of most grey-nomads and campers.
If a user wanted to manually position the dish, they could using a service like DishPointer.com or Wolfram Alpha. This would give a rough alignment and then the tone generator “Point and Peak” for the fine adjustment.
Layer 3 Services
Skymuster services are setup as L2 services.
NBNCo has highlighted from day 1, the option of using Layer 3 for deliver to enable deep packet inspection.
There’s always a lot of talk and opinion about the technologies the NBN employs, it’s effectiveness, etc.
I’ve made a conscious decision to steer clear of opinion in this blog, but there’s often talk and blame shifting between NBNco and RSPs, so I thought I’d cover how the business model works.
Because of this I thought it’d be interesting to write about how the network actually works between carriers (RSPs) and NBNco.
Physical Structure
Last Mile
The last mile in US terms, CAN in Australian Telecom lingo, is connecting the subscriber edge to the network.
NBNCo employs a few different technologies for this, depending on a number of factors;
Fiber to the Premises (Original standard – End to end fibre)
All these last mile services get consolidated and eventually end up at a local PoI – Point of Interconnect, (typically called a POP if you’re any other telco).
These are typically hosted inside exchanges, but not every exchange is an NBNco PoI, if it’s not it uses NBN Backhaul to get to the nearest PoI.
NBNco currently operates 121 PoI sites.
NBNco don’t exclusively use TEBA sites, some are hosted in NBNco “Depots”, there’s currently 10 sites not in TEBA footprints.
At the PoI
Retail Service Providers (RSPs) have to have racks inside the PoI locations, and essentially setup layer 2 cross-connects to the NBNco racks.
Once the traffic is on the RSP network, it’s the RSP’s responsibility to carry it where it needs to go, via their own network / backhaul.
Billing and Metering
Of course, if NBNco is handing off the pipes of customer traffic off to each RSP they need a way to charge the RSPs for this, this is handled by two elements – CVCs equating to the bandwidth at the PoI and AVCs equating to a fixed standing charge per connection monthly.
CVC – Connectivity Virtual Circuit
At the PoI the connection between the NBNco rack and the RSP rack is metered over a CVC – Connectivity Virtual Circuit.
This is shared across all users of that RSP at that PoI.
Let’s say I’m an RSP and I’ve purchased a 1Mbps CVC shared across my 1,000 customers at that PoI, the customers aren’t going to have a good experience.
Of course, CVC bandwidth isn’t free, previously NBNco charged on average $15.25/Mbps.
This had the effect of ensuring each RSP had just enough CVC bandwidth for their customers, but this led to some customers having a poor experience on switching to NBNco as they found their speeds dropped due to not enough CVC bandwidth at the PoI for that RSP.
In June 2017 NBNco announced a change to the pricing structure to try and encourage RSPs to buy more CVC bandwidth to ensure customers speeds weren’t bottlenecked at the CVC.
The new pricing structure makes it more financially attractive to buy more CVC bandwidth based on how many active connections (AVCs) an RSP has in place.
NBNco now charges $17.50 per symmetrical Mbps for each traffic class. (More on traffic classes later)
This means at each PoI the RSP must have a pool of CVC bandwidth large enough to meet the needs of all the customers connections (AVCs) bandwidth needs at that PoI.
AVC – Access Virtual Circuit
NBNco charges AVC fees based on the speed tier the end user will have and the traffic class (QoS) the service has applied.
(This speed tier is regardless of if the RSP has the CVC bandwidth to support this)
Pricing of TC4 (Best Effort) AVCs
Introducing NNIs
NBNco acknolged in Jul 2018 that for some carriers (RSPs) having presence in 121 sites puts up a large barrier to entry.
To counteract this they introduced Network-Network Interface (NNI).
Imagine you’re operating an RSP with a footprint in capital cities and PoI / CVCs in populated areas, you can’t serve customers in remote areas without having a presence at their local NBNco PoI location and buying CVC bandwidth for that location – It just wouldn’t stack up financially.
NBNco introduced the NNI product to essentially backhaul the traffic from these customers to the nearest PoI their RSP is at and share the CVC bandwidth at that PoI.
NBNco’s FTTC technology is accounting for a larger and larger share of the access network mix as the rollout nears completion, but let’s take a look at the hardware doing the heavy lifting.
I won’t go into the fiber network build NBNco are using (Squids, etc) in this post, we’ll just focus on the DSLAM that lives in the pit outside your house, or in NBN parlance – DPU or Distribution Point Unit.
In short, this is a 4 port DSLAM, fed by a fiber service and reverse powered.
The unit itself is waterproof, allowing it to live in the pit outside a customer premises, for FTTC deployments it’s common for every second P3 pit to contain a DPU (each pit typically feeds two premises).
There’s 4 copper tails for connecting in each of the 4 copper pairs to feed 4 premises. The copper run is typically less than 100m and is pretty easy to work out – Pace the distance from your first telephone outlet (TO) to your nearest pit, and there’s a 50% chance that’s the length of your cable run. Because of the short run of cable it’s a lot less to go wrong in the CAN, the only joint on the pair being the one on the DPU itself and anything inside the demarcac.
The DPU is powered by the customer’s modem via a reverse power feed, this means NBNco don’t have to worry about powering the unit, something on FTTN cabinets has been a maintenance headache due to battery backup maintenance.
The lead in cable to the customer premises is joined to the DPU via a “Snot Box”.
Snot box for joining lead in to DPUDPU in the pit
Unfortunately due to the enclosures being water tight and sealed, they don’t have the best thermal management. It’s not uncommon for them to reach 50+ degrees C in the field, which leads to a high failure rate, especially during summer.
NetComm Wireless / Casa NDD-4100
In 2016 NetComm Wireless (Now owned by Casa Systems) signed an agreement with NBNco to provide Fiber to the Distribution Point (FTTdp) Distribution Point Unit (DPU) equipment to NBNco for the launch in 2018, using their NetComm NDD-4100 units.
The unit has 4 ports for customer connections over a VDSL G.9923 interface, with reverse power feed, meaning the unit is fed by the CPE.
For backhaul the unit has GPON G.984 interface.
The device may not be powered at all times so a management proxy caches commands that are fed to the system when it comes back online.
Promo video
Nokia lightspan sx-f
In June 2018 NBNco started trialing Nokia DPUs, and many later installations since then are using the Nokia DPU.
I’ve head a bunch of complains about the NetComm having issues and dying, and for a sealed unit there’s very little debugging that can be done to it.
In the Melbourne office of NBNco there’s a Nokia DPU that’s been running in a fish tank for a number of years.
