Tag Archives: CAN

The role of the telecom Pillar & Cabinet in the Australian copper network

The gray telecom cabinets and pillars can be seen in suburbs across Australia, along rail corridors and even overseas.

But what do they do? What’s the difference between a pillar and a cabinet? Are they still used today? What’s inside? Why are they such an important part of the network?

What are they?

In a nutshell, they’re weatherproof (if properly cared for) enclosures for cross connecting (jumpering) cables.

This means that rather than doing the jumpering / cross connecting services in a dirty pit, a cabinet can be opened and the connection made quickly, in a clean, easily accessed, above ground housing.

They utilise a really clever design, that was the result of a competitive design process in the 1950s.

The schrader valve (bike valve) at the top allows the units to remain pressurized, this means in areas subject to flooding or for pressurised cables, the pillar remains water tight ( although the practice of sealing them again with air isn’t very common anymore).

When the aluminum top plate is unlocked and spun off the threaded fitting, the linesworker can unscrew the big nut on top, and lift up the cover, which locks open at the top, revealing the terminal units (either solder tag blocks or Krone blocks) inside the unit.

Jumpering a service is just a matter of opening up the cabinet, finding the A side and the B side, and running jumper wire through the built in cable management loops from one side to the other.

Each of the Terminal Units is a pre-terminated strip with a few meters of tail, which is fed through the base of the pillar to a nearby pit where they can join 1 to 1, out onto the underground cables, this means the units can be upgraded for additional capacity as needed.

While pressurised they are IP67 rated, but this only goes so far, check out this Telstra photo from Queensland Floods in 2010 from Taroom. https://www.flickr.com/photos/telstra-corp/5362036747/in/album-72157625841011142/
While pressurised they are IP67 rated, but this only goes so far, check out this Telstra photo from Queensland Floods in 2010 from Taroom.

Why were they needed?

  • Cables are expensive. We want to minimize excess unused pairs and use the existing pairs with maximum flexibility and efficacy
  • Opening joints costs time, money, and risks disturbing other services. We want to avoid opening joints
  • Troubleshooting is also time consuming and costly. A convenient test point is needed for isolating where in a cable a fault lies. (Main Cable, Distribution Cable, etc)
  • Easily use gas/air filled cables, without having to constantly open and reseal cables them to splice in new joins / jumpers

Cabinet vs Pillar

Cabinets and Pillars look the same, but the hints as to their purpose are in their location and what’s sprayed on them in faded paint.

Pillars are used for cross-connecting main cables (“M” Pair from the exchange) with distribution cables (to subscribers “O” pairs which run down the street to the pit in the front of your house).

Pillars are generally stenciled with a “P” and an number, or just the DA (Distribution Area) number.

Cabinet are a more flexible setup where you can connect cables between Pillars, akin to a root & branch approach.

Cabinets cross connect Main Cables (“M” pair to the exchange), with Branch Cables (“B” Pair from the Cabinet to Pillar) and Distribution cables (“O” pair to the customer).

Cabinets are stenciled with the prefix “CA” and a number, and exist in the 900 and 1800 pair variants, where one is just taller than the other.

The blue example is direct from the Main Cable to the Pillar, while Cabinets are used in the black example.

This means the distribution can go via a Cabinet to the Pillar to the Customer, as shown in the top /grey lines in the diagram.

  1. Exchange Main Cables (Main Cables / M-Pairs) go to Cabinets
  2. Cabinets connect to Pillars (Branch Cables / B-Pairs)
  3. Pillars connect (Distribution Cables / O-Pairs) that run through the pits outside houses
  4. Inside the Openable Joint in the pit is used to connect the lead in cable from a subscriber’s premises

Alternatively, the Cabinet may be bypassed and a direct cable goes between the Exchange and the Pillar, in that scenario it looks like the one show in blue lines on the diagram.

  1. Exchange Main Cables (Main Cables / M-Pairs) go to Pillar
  2. Pillars connect (Distribution Cables / O-Pairs) that run through the pits outside houses
  3. Inside the Openable Joint in the pit is used to connect the lead in cable from a subscriber’s premises
Display of 300, 900 and 1800 pair pillars and cabinets at the former Telstra Museum in Hawthorn

The Cabinet to Pillar model fell out of favor due to its increased complexity.
While it was cheaper to deploy the network using cabinets that cascaded down to feed pillars (you would only have to install enough cable for the “here and now” and could add additional Main & Branch cables as needed in a targeted manner) the move to outsourced lineswork for Telecom found that any increased complexity, led to additional operational cost that outweighed the capital savings

Use in the “Modern” Copper Customer Access Network

Pillars are still used in areas of Australia where NBNco have deployed Fibre to the Node.

NBN adds a row of X-Pairs (VDSL) and C-Pairs (Channel) to the pillar, which connect into the FTTN nodes themselves.

This means a customer with a traditional POTS line (M-Pair from the Exchange, C-Pair from the Cabinet to the Pillar, O-Pair from the Pillar to the Pit, and then the lead-in into their property) has the O-Pair and C-Pair buzzed out on the pillar, and then routed through the X-Pair and the C-Pair on the Node.

This puts the DSLAM in the Alcatel ISAM inline with the customer’s existing copper loop to the Exchange. The main cable comes from the exchange onto the M-Pair blocks in the Pillar, is jumpered onto the X-Pairs which go through the DSLAM, and come out as C-Pairs back onto the pillar. The C-Pair is then jumpered back to the Customer’s O-Pair and bingo, the FTTN cabinet is inline with the copper loop.

However as the PSTN services get dropped, the Main / M-Pair to the exchange can eventually be removed and the cables removed, meaning the connection just goes from the C pair for VDSL out into the O pair to the customer.

As part of the NBN migration some pillars were upgraded to include IDC / Punch Down blocks, and a rectangular version of the pillar was introduced.

NBN pillar

Oddly, these rectangular covers, do not have rectangular units inside, but rather cylindrical ones, just like the pillars of old.

This does fix the missing lids issue – The lid is captive, but I’m not sure what other design improvements this introduces – if anyone has the insight I’d be keen to hear it!

Tiny Pillars in the CAN

On the rare occasions I’m not tied to my desk, I’m out for a long run along some back roads somewhere.

Every now and then I come across these tiny telecom pillars for cross-connection (and don’t shoot at them) – I mostly find them around the edges of distribution areas.
I had some recollection that these were originally for trunk lines between exchanges (maybe there was some truth to this?), but some digging in old docs show these were just for interconnecting main or branch cables with distribution cables, in areas where the 600 and 1200 pair pillars / cabinets would be overkill.

They’re built like the 900/1800 pair cabinets, but just scaled down versions, supporting 1x 100 pair main cable, 1x 100 pair distribution cables and 2x 50 pair distribution cables.

It seems like these were largely decomed when NBN took over, leaving most with a big X sprayed on them.

While I was looking through the docs I also found reference to a 180 pair pillar, which looked very similar, but I’ve yet to see any of them left in the wild. Better keep running ’till I find one!