Further to our blog entry about Submarine Repeaters, here is some history of the technology used.

The first generation optical fibre cable systems, repeaters or 'regenerators', were placed along the cable periodically to boost the optical signal.  Each regenerator was comprised of a receiver, to convert the optical signal to a digital electrical signal;  a regenerator to work out whether each incoming pulse was a ‘1' or a ‘0' and to generate a new one; and a transmitter (laser) to convert the new digital pulse into an optical one for transmission over the next fibre section.

Although robust and reliable, the key disadvantage of this technology was capacity:

• The regenerator circuits installed along the cable were preset to operate at one transmission rate (‘bit-rate') and could not be changed later, and
• The regenerators were only able to process or ‘regenerate' one set of data (wavelength) at a time making them incompatible for use with WDM.

PPC-1's survey vessel, The Gelendzhik, is currently in the Bismarck Sea off Papua New Guinea (PNG). Branching units in both Madang and Port Moresby are planned for PNG.   

The Gelendzhik is now halfway through surveying the route from Guam to Sydney, and from here will continue through the Solomon Sea and down the Australian Eastern Seaboard to Sydney.  The survey is expected to be finished in early July.

You can see the overview of the entire route in the Geography section of the website, and follow the progress of the survey operations on the PPC-1 Progress page.

Work in the Cable Landing Station in Sydney is progressing well with the struts to support the cable tray being installed. The photo above just shows the tray for the switchroom. The position of the switchboards has also been marked out to ensure that the tray is put in the right places.

The core holes and penetrations between the different rooms and outside are drilled and the unnecessary toilets have been removed.

More photos are available in the album "Sydney Cable Landing Station Update" in the gallery.

Recently we installed a joint on the corner of Pittwater Rd and South Creek Rd in Dee Why, approximately 3kms from the Cable Landing Station at Cromer. 

The joint will allow for future capacity expansion once PPC-1 is operational.  The joint is a 16 port system, with one cable going in, and 15 cables coming out.  The full process of installing this joint is illustrated in the "Cable Joint at Dee Why" album in our gallery.

The ‘capacity' of a submarine cable refers to the total amount of data bits it can transport per second.  Increasing the number of fibre-pairs in the cable is one method of increasing the cable's transmission capacity, but bearing in mind that each fibre requires dedicated amplifiers to boost the signal periodically, the number of fibre-pairs is generally limited by the number of amplifiers that can practically be accommodated within a repeater casing.  For PPC-1, 2 fibre-pairs have been chosen.

The second method is to reduce the duration of each light pulse (‘bit') such that more bits can be transmitted per second.  The laser transmission rate PPC-1 is 10Gbit/s - that's 10 billion laser on's and off's per second.

The third technique is to couple multiple lasers to each fibre, each transmitting a slightly different colour (wavelength) of light and each carrying separate data.  By filtering the light received at the far end into the original colour components, it's possible to recover the data transmitted on each wavelength.  This technique is known as Wavelength Division Multiplexing (WDM) or Dense Wavelength Division Multiplexing (DWDM) where a large number of closely spaced wavelengths are used.

Each fibre on PPC-1 has been designed to support 96 wavelengths, each operating at 10Gbit/s.  The total transmission capacity of PPC-1 is therefore:

2 fibre-pairs x 96 wavelengths x 10Gbit/s = 1920Gbit/s or 1.92Tbit/s.

To put this into perspective, a basic telephone conversation typically requires 64kbit/s to transmit.  If the entire population of Australia made overseas calls at the same time, it would require only 1.3Tbit/s of capacity.  This underlines the very significant impact that PPC-1 will have on Australia's international telecommunications capacity.

Since the late 1980s, submarine cable systems have employed optical fibres as the primary transmission medium.  Optical fibres are essentially flexible glass strands designed in such a way that light injected into the fibre travels along it, even around bends, without leaking out.

Similar to the early telegraph cables fibre, optical communications is a digital technology in that it carries ‘pulses' (ons and offs) of light, in this case, which represent the ‘1's and ‘0's of the data being transported.  The characteristics of the fibre enable the pulses to travel long distances before they need to be amplified - typically a pulse will lose half of its optical power over a distance of 15km of fibre. 

Accordingly, over transoceanic distances it's necessary to periodically amplify the light pulses travelling down the fibre.  The spacing between amplifiers depends on many factors such as the pulse or ‘bit' duration, the total length of the cable and the total design capacity of the fibre.  For PPC-1 the amplifier spacing is approximately 93km.

Separate fibres are used for each direction of transmission, so for bi-directional communication, a pair of fibres (and their associated amplifiers) is required.

Last week while at Tyco Telecom's Labs, we undertook interoperability testing between the Foundry MLX routers used in PIPE Networks' domestic MPLS network, and the Tyco Telecom SLTE equipment used to terminate the submarine cable system.

This interop testing is designed to establish that the Foundry MLX routers operate correctly over the Tyco Telecom submarine equipment, enabling PIPE Networks to extend its domestic MPLS network internationally once PPC-1 is complete.

During the testing process we tested the performance of PIPE Networks'  standard MPLS products over a lab-based submarine system using STM-16 (2.5gbps), STM-64 (10gbps), 10G LAN PHY and 10G WAN PHY interfaces.  Importantly, in the lab we were able to introduce realistic levels of latency to assess the impact of nearly 7000km of fibre network between the routers.

The actual performance testing was done using a Spirent Smartbits network analyser with two 10 gigabit interfaces, with a couple of the tests being repeated on an Agilent N2X tester to confirm the results.

The primary terrestrial fibre has now been hauled to the outside of the cable landing station. The cable is attached to a draw wire that is run on a winch. The winch has a big wheel (at an angle) that's used to pull the cable through. The wheel ensures that the cable is not bent beyond the designed ‘bend radius' as bending it too far can cause the fibre to fracture or break.

In addition to maintaining the bend radius, the winch also lets you set the maximum cable tension for the haul.  A 'clutch' is automatically engaged should the hauling tension reach the maximum tension allowable under the cable specification.  This ensures that the cable is not damaged during the hauling process.

There will be one final road crossing to reach the station and this will be done once the internal station fitout works are almost complete.  Until then, the fibre loop will be left coiled up in the manhole.

The next job will be to complete the diverse fibre route to the same position before it too is installed inside the cable landing station.

The above photo is an example of the optical repeaters to be used on PPC-1.  The repeater will contain two fibre pairs on the trunk between Sydney and Guam.  They're spaced at regular intervals along the cable and their main task is to amplify the transmission signal as it propagates down the fibre.   The repeaters are powered by a DC 1A current running down the copper conductor of the cable.

To avoid disturbing the beach at the landing point at Collaroy a 2000m long Horizontally Drilled Duct (HDD) will be bored seawards from a location back from the beach at Collaroy.  The exit point of the bore will be in approximately 15m of water such that the main cable layer can approach and subsequently install the shore end cable into the HDD.  A messenger wire is left in the HDD after drilling is complete.  The messenger wire is used to install a winch wire just prior to the ship arriving.

HDD methods are well known in the oil and gas and construction industries as an alternative to disturbing sensitive environments and/or avoiding otherwise difficult installation areas.  More traditional methods such as pit and pipe or direct burial techniques are less favoured in a number of cases where disruption or environmental damage would occur.   We intend to install a single HDD bore that will be a standard drill string or a HDPE lined steel pipe that has a minimum internal diameter of approximately 90mm.  The cable to be installed will be smaller than 30mm outside diameter.

The trajectory of the HDD needs to be precisely controlled to ensure that the resulting bore is a simple curve in two dimensions (i.e. it has no compound curves).  This is done to ensure the installation tensions on the cable and winch wire are kept as low as possible. The figures above illustrate the concept of a HDD installation from shore and the pumping of fresh water into the drill pipe as the bore exits the seabed which minimises any leakage from the end of the pipe.