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Why does gigabit internet via coax cable not offer symmetrical speed like fiber?
- R0BERTGLICK 7y agoThat was an interesting article thanks for sharing.
- vkdelta 7y agoBecause simply US (upstream) frequencies are limited to 42 MHz or 85 MHz. They start at 5 MHz. While in most cases downstream frequencies start from 54 MHz to 1 GHz
- rocqua 7y agoBesides this, coax is 'half duplex' until you apply Frequency division. Hence every bit of upload costs you bandwidth on the download side. At the same time, fiber is full duplex so this is much less of an issue. The difference is that applying a voltage at the transmission side in coax will be noticed by the receiver, (cause electricity goes both ways) whereas shining a light into fiber doesn't get to the detector (because light only goes one way). At least, this is my limited understanding. Would love if anyone more knowledgeable could correct me.
- zamadatix 7y agoFiber is very often frequency divided to give full duplex on a single strand to customers. Or the concept is taken to the extreme e.g. GPONs.
- snuxoll 7y agoGPON is time divided, not frequency divided. You have one wavelength for Tx and one for Rx and everyone on the PON has to split it. It is certainly POSSIBLE to do WDM on a PON, but you need separate matched pairs of transceivers for each connection which kind of defeats the purpose (you now need a mux/demux at the end which adds more attenuation to the line, as well as more expensive electronics as you went from needing one GPON port to N Gbe ports). As such, wavelength division is typically used over point-to-point links to get more discrete links over a single fiber (or pair).
- sathackr 7y agoGPON is both time divided and frequency divided. There are typically 3 wavelengths.(frequency division). Two for data(downstream and upstream) and one for video (downstream). The downstream channels(both video and data) are broadcast and not time divided. The streams are filtered by the ONT. The upstream data channel is time divided to permit multiple devices transmitting without collision.
- sathackr 7y agoBoth cable and FTTH(single-strand fiber to the home, such as Fios) are full-duplex via frequency division. Cable operates in RF bands, and frequencies are denoted in MHZ and sometimes GHZ(included in the linked answer) Fiber operates in optical bands and frequencies are denoted in nanometers(wavelength) -- downstream data, downstream video, and upstream data are all operated on different wavelengths on the same piece of glass, and they are received at both the transmitting end and the receiving end. They are typically separated and filtered by optical prisms to ensure the correct wavelength hits the correct receiver(most receivers are wide-band and will receive a wide range of optical wavelengths) The medium is typically shared at a neighborhood level, in that a single optical strand may be split 16 or more times to serve multiple houses. Bandwidth is shared on that strand by the houses served by it, typically via TDM(time division multiplexing) End users don't typically notice this because the line rates are higher than the maximum bandwidth package sold. IE downstream rate 2.5Gb/s, upstream 1.5Gb/s, max package available is 1Gb/s. Edit: removed incorrect statement regarding gepon/csma
- rocqua 7y agoHow come fiber can't use the same frequency for uplink and downlink? Coherent and focused laser light only travels in one direction, so I'd expect the transmission not to interfere with the receiver.
- sathackr 7y agoDuplex fiber where a separate strand for TX/RX can use the same frequency. Simplex fiber, that is point to point, may in fact be able to use the same frequency, but it's not done in practice. Possibly due to the difficulty in directing the outgoing and incoming signals to different pieces of hardware(receiver and transmitter) GPON networks(typically used by Fios, etc...) have multiple passive splitters on the strand. For example, a common PON splitter would have 1 strand in from the OLT(optical line terminal, essentially the head-end), 32 strands out. The light received from the OLT is split x32 and sent to each downstream port. The devices on the downstream ports(ONU/ONT, Optical Network Terminal) receive this signal and also transmit it on the same strand. That transmitted signal must be coupled back into the single upstream port, from every attached ONT. I imagine there is significant difficulty getting the light to traverse the splitter and exit only via the upstream port. So a different wavelength is used so that it doesn't matter if the light is received by the other units, and also it can be more easily filtered (by wavelength instead of direction). My knowledge of optics is not sufficient to fully explain why it's easier to filter by wavelength instead of direction.
- Dylan16807 7y agoI'm sure you could do full duplex coax if you really wanted to. But it's not worth the effort here.
- aaronax 7y agoI'm not sure that you would find any product on the market which shines the same frequency of light in both directions on a single fiber. All of the bi-directional on a single fiber products that I know of send a different frequency of light in each direction. Therefore it would seem strange to me to claim that a single strand of fiber can do full duplex, as frequency "B" of light could instead be used to send data in the same direction as frequency "A". So really you are just choosing to allocate some part of the overall capacity of the single fiber to return traffic.
- madengr 7y agoYou actually can separate out the forward and reverse waves on a coax, but it requires good impedance match on both ends, and some transformer based magic-Ts. So you can do full duplex on a single coax, sharing the same bandwidth. It’s just not practical in long runs since you’ll only get 20 dB isolation between directions. A common use is carrying Ethernet over coax when retrofitting analog CCTV cameras to IP cameras, and you don’t want to run new cable.
- the_mitsuhiko 7y agoThat information is quite outdated. It's more than possible to get symmetric speed on (EURO)DOCSIS 3.1. The main reason it does not happen is because there is no consumer demand for it.
- techntoke 7y agoAnd Comcast has the seventh largest lobbying budget of any individual company or organization in the United States. ISPs should be regulated like public utilities.
- seganddr 7y agoMakes you wonder about the origin of the OP.
- wongarsu 7y agothe_mitsuhiko is from Austria (according to his keybase linked in his profile). But it shouldn't matter, if there's no consumer demand then lobbying is irrelevant.
- dang 7y agoPlease don't post insinuations of astroturfing to HN unless you have some sort of objective evidence to point to. This is one of the most common and most poisonous internet tropes around, so we have an explicit rule against it in https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html. More explanation at https://hn.algolia.com/?sort=byDate&dateRange=all&type=comment&storyText=false&prefix=true&page=0&query=by:dang%20astroturf https://hn.algolia.com/?sort=byDate&dateRange=all&type=comme... if interested. Edit: looks like you've done it at least twice before. That's too much. Please read https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html and stick to the rules when posting here.
- zamalek 7y ago> there is no consumer demand for it. The most demanding thing more than, probably, 0.01% of customers do is livestreaming. If your line can actually sustain 10mbps (vs advertised/claimed), you're good. The only other real scenario is someone learning that they have to back their data up, for the first time, which is really a once in a lifetime usecase for fast upload. What would likely improve the experience of 99%+ users is latency, where fiber has consistently proven to be king (for me at least).
- electriclove 7y agoI don't buy the 'no demand for it' line. It has never been offered by the big players. They don't want consumers uploading large amounts of data. I suspect this was originally done due to piracy concerns. But with so many homes having Nest products (and the like) that constantly upload, we need higher uplink speeds.
- jethro_tell 7y agoWell, it was originally for cost concerns, when you have a limited number of channels. eyeball Network tend to want down speed.
- swebs 7y agoClick the article. The guy asking on Superuser says that fiber services like Century Link have symmetric upload speeds.
- filoleg 7y agoPretty much all fiber services around Seattle offer a symmetric gig (CenturyLink, WaveG, Google Fiber/WebPass). The only caveat I’ve heard of is that in some older buildings, WaveG offers only non-symmetric 1Gb down/100Mb up, but i am yet to encounter that myself. I didn’t look into this myself, but i have a feeling that one might actually be just a DOCSIS instead of the real fiber.
- the_mitsuhiko 7y agoMost fiber services use GPON which also reserves less bandwidth for uploads.
- lawnchair_larry 7y agoISPs do not care even a little bit about piracy. The only reason piracy is an issue for them is because it hogs bandwidth, not the other way around.
- 7y ago
- christocracy 7y agoWhile I stewed after the dotcom crash during early 2000s, I had a short 2-year gig working as a headend tech for a small cable company. It’s not about demand, it’s about climbing poles and rolling bucket-truck crews to replace filters and other expensive equipment on a massive scale. The top comment in the link there is spot-on. https://superuser.com/a/1519918 https://superuser.com/a/1519918 I was involved with the “digital switchover”, moving the traditional analog channels over to the digital QAM channels, potentially freeing those now duplicated analog channels for upload channels. Maybe more upload is technically possible but the work on the poles is going to be expensive. [edit] oops, pasted duplicate.
- CriticalCathed 7y agoPriorities, right? I wonder what their business would be like if they had the foresight to not make the split so lopsided.
- k__ 7y agoI still don't understand why DSL connections have the same issue
- blattimwind 7y agoThey don't, it's a question of DSL profiles. Commonly used consumer DSL profiles have a 8:1 to ~2:1 ratio because that seems to match well with consumer usage. Business DSL generally is symmetric. 1000 MBit/s downstream, 35 MBit/s upstream is an 30:1 ratio, far more extreme than any DSL profile.
- ndespres 7y agoDSL, at least ADSL commonly found in homes, is designed that way as a good way to split the frequency available on the line to match what people need. It also shares a good portion of the frequency with POTS telephone service. There are SDSL (symmetric DSL) standards which provide fully symmetric bandwidth on the circuit. Not sure how popular it is these days but when I supported it at an ISP about 10 years ago, it was a cheap alternative to T1-class circuits.
- Hamuko 7y agoMy ISP will not sell me anything better than 1G/100M on fiber. Maybe if I looked into business plans maybe.
- 3fe9a03ccd14ca5 7y ago1 gbit non-fiber is all but marketing. For starters they have a small bandwidth caps, which keeps you from doing anything interesting. Another thing like the article mentions is that it’s a meager upload ability. I have symmetrical gigabit fiber at my house. When a new Ubuntu torrent drops I’m able to seed a TB relatively quickly. Bandwidth caps would make it so much less useful and interesting.
- tonyb 7y agoI do quite a bit of DOCSIS consulting. There are both technical and business reasons for the gap between upstream and downstream speeds There are a few technical reasons. There is less upstream frequency available in the upstream. 42 MHz is the standard upstream/downstream split, 85 MHz is a midsplit, 200 MHz is a high split, and the downstream goes up to 1Ghz or even 1.2Ghz. The upstream modulation runs at 64 QAM (~27Mbs) and downstream modulation runs at 256 QAM (~38 Mbps). The upstream is also more sustainable to interference and impairments. So the technology is inherently imbalanced. From a business prospective it is very difficult to cost justify. Moving the upstream/downstream split and/or upgrading to DOCSIS 3.1 is very expensive. The reality is that the typical customer use very little upstream bandwidth. It isn't uncommon for me to see a node with 24 or 32 downstream channels at 80% usage and 4 upstream channels are at 25% utilization or less. We see a downstream to upstream usage ratio of about 15:1. If you move the US/DS split that means you are taking away from available downstream frequency which means less DS data bandwidth or fewer video channels. It's hard to make a business case to invest in increasing upstream bandwidth when the data says people aren't going to use it. Newer technology like DOCSIS 3.1, Docsis FDX, Remote PHY and modern plant designs like N+0 or N+1 (which means fewer customers per node) will bring higher upstream bandwidth, but it will be awhile before we see anything close to symmetrical speeds.
- Namidairo 7y agoYou should take a look at Australia, where we try to shove hundreds of customers onto a single node (Up to 900 per node, up to 250 per segment). Edit: Although it wouldn't be fair to leave out that it's a EuroDOCSIS 3.0 setup with 16/4 downstream/upstream, with very limited 3.1 being used on a small scale.
- samstave 7y agoIsn't telstra just riddled with stories of corruption over time? https://www.channelnews.com.au/key-telstra-5g-partner-admits-to-bribery-corruption/ https://www.channelnews.com.au/key-telstra-5g-partner-admits...
- 7y ago
- pwarner 7y agoI don't think we need symmetrical, but could we get 4:1 ratio instead of 20:1 please? PIN fiber that Verizon FiOS uses is 4:1 at the physical layer, or it was with BPON and GPON standards. I did not follow. I imagine they can sell symmetrical since most people don't use much upstream. Oversubscription is standard and works great in almost all cases.
- pg_is_a_butt 7y agoWhy aren't electrons photons?
- zw123456 7y agoFiber can also have asymmetrical speeds (see GPON, NGPON2 etc.). The issue is not the media per se but the concept of shared media. Take any media, wireless, coax, fiber, even copper (ADSL) you have X amount of spectrum to work with so you have to decide how allocate said BW. Since most users demand is higher for downstream than upstream (typically you are downloading a lot more than uploading) it makes sense to allocate more to downstream. Of course it is possible to have full duplex symmetrical speeds. Say you want to allocate 2 fibers, on for upstream and one for downstream, then you can have symmetrical speeds. But typically due to costs, you want to have one fiber shared between a large number of users (e.g. GPON or NGPON, aka FiOS) or one coax shared amongst many users, or some set amount of RF spectrum, in any case you need to make the same type of trade off choice that the cable provider makes or that the DSL provider makes or wireless providers. In the case of wireless the reason that uplink is so much weaker is due to the limited power of the user equipment, also smaller antenna etc. refer to Shannon's law, uplink will be weaker. But generally speaking, it makes sense to have asymmetrical speeds unless you have the luxury of having the same spectrum and power available for both directions.
- wbl 7y agoDirectional couplers are a thing. Thomas Edison patented multiplexing techniques for telegraph wires that didn't even need them.
- jrockway 7y agoI think the fiber industry prefers wavelength division multiplexing over simple directional couplers. You can certainly have multiple 10Gbps customers on a single strand of fiber with passive equipment, and many ISPs will happily sell you such a circuit. (Gpon, mentioned above, is mostly time division multiplexing. I have worked for 2 ISPs that use gpon, and we've never sold anyone an asymmetric plan, except for the "free plan" that Google Fiber had. Gpon is perfectly happy to be symmetric, but it does have a limited bandwidth shared between multiple subscribers.) The biggest problem I've found is that the Internet isn't really ready for customers that can download at 10Gbps. When I set up a 10Gbps connection for myself, I had a lot of trouble finding anything on the Internet that would send me data that quickly. Even my own servers were AWS instance types that only supported 5Gbps burst. So that is probably the reason why you aren't seeing consumer ISPs selling you 10Gbps circuits... even the servers don't have 10Gbps! A new wave of upgrades are needed for this to become viable; 100Gbps networking equipment is still pretty expensive.
- shmerl 7y agoBecause ISPs are cheapskates and don't want to upgrade their networks and hardware. There are better exceptions, like Altice who are in the process of replacing their coaxial network footprint with fiber optics. Interestingly, according to them it will actually cause them to save money in the long run due to lower maintenance costs for fiber optics. I guess other coaxial ISPs are too greedy for short term profits to look ahead.
- magoon 7y agoNot mentioned, they don’t want to support residential customers serving web sites (or anything else)
- kazinator 7y ago> Cable TV, before DOCSIS cable modem internet service became a thing, didn't need much upstream bandwidth. All the upstream was needed for was to authenticate the cable descrambler set-top boxes, authorize occasional pay-per-view transactions, and maybe do a few minor "interactive TV" things, like letting you check your cable bill from your descrambler box. Cable TV didn't have any upstream signaling once upon a time; it was a purely a system of repeating and replicating an analog signal in the downstream direction. Early scrambling methods for "pay TV" channels could be undone using circuits that were published in electronics magazines.
- to11mtm 7y agoMostly true. But upstream signalling predates cable modems by a certain period; originally the upstream was intended for things such as city 'public access' stations to feed back to the headend (to then be transmitted back out to customers). It's existence was certainly handy for the use of cable modems.
- kazinator 7y ago> Mostly true. Where lies the falsehood?
- in3d 7y agoA fiber network Hotwire offers max 1 Gbps download and 50 Mbps upload in South Florida. Oh and it’s a 2-year contract if you want those speeds.
- parski 7y agoIs bandwidth speed?
- z3ro 7y agoI think it's a conspiracy/scam, so they can milk every dollar out of every company that wants to peer with them. The only way to peer for free is if your traffic profile is 50% send and 50% receive. Cable companies offer these asymmetric pipes to their customers to make this balanced traffic profile impossible to achieve, so everyone ends up paying the cable companies big bucks for transit on their network.
- charwalker 7y agoI can about triple my internet bill to double my uplaod speeds and still be about 50% off what I need for things I run at home. Media streaming from my own server is possible for 1-2 people at 720p/mbps and I want that pushed to 1080p minimum. A business class connection might get me there.