0

If I establish a TCP connection between a web browser in an Australian household laptop, and a web server in a US data centre, what chain of physical hardware will the signal be sent through?


For example, consider something like the Hawaiki cable: roughly a half-billion dollar cable to carry 70Tbps across the Pacific (from Sydney to Portland).

Are such backbones now exclusively fibre-optic? Roughly what diameter would this cable be? How many independent fibres would carry information? Does each fibre carry many individual channels of information, and if so how (e.g. different frequencies of light or some other mode)? What rate of information is sent in a single channel, and is it encoded simply by flashing on and off? Is some form of active repeater needed at regular lengths or can the signal propagate under an entire ocean?

What hardware connects to the ends of the cable? I presume the bandwidth initially gets distributed among a dozen or so smaller backbone links and data centres. I'm thinking no conventional router could handle Tbps (as it would need to transfer thousands of bits per modern CPU cycle). Does classic IP routing ever really happen on a bulk scale, or are different sub-bundles passed directly (through some kind of mass repeater device) to smaller backbone links? Perhaps with a braid (to make distinct physical routes between any endpoint at one end and every endpoint at the other)? Or does it fan out into tens of thousands of standard gigabit connections, each patched into its own rack..? In other words, how are the end-nodes of internet backbones actually implemented?

5
  • Please don’t aggregate 20 different questions into one post. It makes it hard to answer specific parts of your questions. Also, there are plenty of tutorials on the internet which explain many of your questions.
    – Teun Vink
    Sep 21 at 16:28
  • @TeunVink feel free to ignore everything below the horizontal line (it was meant only to clarify).
    – benjimin
    Sep 21 at 21:22
  • First, home networking is explicitly off-topic here, and questions about networks not under your direct control are off-topic. You would need to ask the network owners about what they are using.
    – Ron Maupin
    Sep 21 at 21:33
  • @RonMaupin this question is explicitly not about consumer grade networking. Is there a more appropriate stack exchange for questions about the engineering of large-scale network infrastructure?
    – benjimin
    Sep 22 at 0:27
  • You are referring to a home network in the question, and the networks between your home and the server are not under your direct control.
    – Ron Maupin
    Sep 22 at 0:49
4

Details will obviously vary and i'm not an expert but i'll try to answer the question from what I understand.

web browser in an Australian household laptop, and a web server in a US data centre

Data from your laptop will pass through a series of diverse networks, it will first pass through your ISPs access network, then into their core network. Depending on their size and business model they may buy IP transit service from larger provider locally or they may buy their own capacity on an intercontinental route to get it to the US.

When it gets to the US it will likely be passed on to a major IP transit provider, and from there to the provider that hosts the server.

Providers will choose equipment based on their capacity needs. The networking world is increasingly trending towards Ethernet based technologies, but I'm sure there is a lot of legacy stuff about.

Are such backbones now exclusively fibre-optic?

Intercontinental internet data is indeed nearly always carried on fibre optical cables. Copper cables don't have the capacity and satellites usually have latency issues.

Roughly what diameter would this cable be?

Wikipedia claims about an inch. Very little of that is the actual fibers, most will be mechanical reinforcement and power conductors.

How many independent fibres would carry information?

Generally, because of the need for repeaters, long distance undersea cables have less fibers than terrestrial or short distance undersea cables. Your particular cable seems to have a total of 3 fiber pairs on the core of it's route. https://www.submarinenetworks.com/systems/australia-usa/hawaiki-cable

Does each fibre carry many individual channels of information, and if so how (e.g. different frequencies of light or some other mode)?

Yes, wavelength division multiplexing is used.

What rate of information is sent in a single channel

It keeps increasing, I have certainly heard of 100GBPs per lambda (wavelength) but more may well be possible now.

You hit a point of diminishing returns though, because once you modulate a signal it no longer has a single wavelength. So as you increase the capacity of each lambda you find you have to space them further apart.

and is it encoded simply by flashing on and off?

It used to be (and may still be on older cables), but nowadays more advanced modulation systems are used.

Is some form of active repeater needed at regular lengths

Yes, optical amplifiers are used. As I understand it there are two main types. Erbium-doped fiber amplifiers (EDFAs) which provide point amplification and Raman amplifiers which provide amplification in the infrastructure fiber leading up to the amplifier. As I understand it the two types are often used in conjunction.

Crucially optical amplifiers can amplify the wavelength division multiplexed signals without de-multiplexing and re-multiplexing them. However they do have a limited wave band, so there are still limits on capacity.

What hardware connects to the ends of the cable?

There will be equipment to split out the wavelength divison multiplexing, then special transciever units to convert that to or from formats that can be used to pass it on to other equipment.

I'm thinking no conventional router could handle Tbps

Routers have been getting bigger, Cisco advertise routers with a capacity as high as 260TBPs https://www.cisco.com/c/en/us/products/routers/8000-series-routers/index.html#~benefits

(as it would need to transfer thousands of bits per modern CPU cycle).

High end routers don't use CPUs to route.

Does classic IP routing ever really happen on a bulk scale,

Sometimes it does, but undersea cables are not usually owned directly by any individual ISP.

So the cable operator will sell wavelengths to ISPs that want them. The individual ISPs will then provide their own IP routing equipment of suitable capacity for their needs.

Typically an ISP will have it's own equipment at both ends of a long distance link. Interconnections between providers generally happen over local links within a city (or even within a datacenter).

3
  • once you modulate a signal it no longer has a single wavelength - frequency modulation isn't used with fiber (AFAIK), but amplitude modulation has just been introduced for high speeds (PAM-4 with two bits per step with e.g. 100GBASE-LR1). Cutting edge is 16QAM developed for 400GBASE-ZR (400 Gbit/s over 80 km), albeit using DWDM.
    – Zac67
    Sep 21 at 16:04
  • You don't need frequency modulation to get a non-zero bandwidth, any modulation will do, though some will spread the signal more than others. Light isn't fundamentally different from electrical signals in this regard other than having a much higher frequency. Sep 21 at 17:35
  • The bandwidth of an EDFA seems to be about 10 THz, Large certainly but not unimaginably so given the data rates already being run over submarine fibers. Sep 21 at 17:41

Not the answer you're looking for? Browse other questions tagged or ask your own question.