
Why does gigabit internet via coax cable not offer symmetrical speed like fiber? - personjerry
https://superuser.com/q/1519893/529428
======
tonyb
I 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
You 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
Isn't telstra just riddled with stories of corruption over time?

[https://www.channelnews.com.au/key-telstra-5g-partner-
admits...](https://www.channelnews.com.au/key-telstra-5g-partner-admits-to-
bribery-corruption/)

~~~
nojvek
Telstra is the equivalent of Comcast here. They’re monipolies in large parts
of the country so they can get away with a lot

~~~
MrMorden
And NBN's wholesale charges are comparable to what a retail ISP in a
competitive market (e.g. Stockholm) charges for symmetric 10Gb/s FTTP.

[https://www.itnews.com.au/news/nbn-co-puts-future-
residentia...](https://www.itnews.com.au/news/nbn-co-puts-future-residential-
arpu-at-49-a-user-530383)

~~~
wbl
You could run a lot of websites on that.

------
christocracy
While 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
Priorities, right? I wonder what their business would be like if they had the
foresight to not make the split so lopsided.

~~~
k__
I still don't understand why DSL connections have the same issue

~~~
AviationAtom
DSL is dedicated all the way back to the central office, so it doesn't have
the same problem as cable has. That said, what others posted is correct, home
users download far more than they upload, so it makes sense from a marketing
perspective to give far more downstream bandwidth than upstream. Home users
tend to appreciate having a high download speed much more than having equal,
but much lower upload and download speeds.

Other interesting info: ADSL is dreadfully slow by today's standards, but VDSL
can actually hit some decent speeds. The big problem with both is attenuation
of copper wire is fairly significant over the distance the lines generally
travel, much more so with VDSL, due to it's higher frequency range. That's why
companies like AT&T, with their U-Verse brand, bring fiber to the
neighborhood, to lop of a significant distance of copper. They can increase
the distance they service by making use of two lines paired together. AT&T
takes a portion of legacy ADSL service now and puts VoIP over it, with the
VDSL service having more than half it's capacity generally devoted to IPTV
bandwidth. One single good condition line could generally carry 118 Mbps, but
they would split that up for TV, leaving only 45 Mbps. Now they are mostly
pushing FTTH/FTTP though, leaving no option for POTS/copper. That is all good
though, because most the copper run is such garbage that it absolutely sucks
being a technician. You would be gigged for the line runs getting water in
them and making service drop out, even if everything tested great when you
installed, or even if you turned a ticket in the line techs might kick it back
and say everything is fine.

~~~
milankragujevic
I'd also like to mention something that was tried in Serbia (but ultimately
failed, though in a good way):

Our national telecom operator, Telekom Srbija, had a monopoly on internet
access in most areas due to the fact they own all the phone lines. In
cooperation with Huawei and the Chinese and Serbian governments, they made a
plan to kill POTS service per line and use ALL of the bandwidth for VDSL, as
well as building DSLAMs on street level, to provide very high speeds (100/10
Mbps was the max they achieved before stopping) with short copper lengths.
Phones would work over VoIP, so all new modems were VDSL compliant with IAD
(integrated access device) "certification" (a SIP client and 2 POTS ports).

In the end the Chinese lost interest and it was all forgotten and covered with
ash. The new idea, which is why I say it failed in a good way, is to skip the
street DSLAM buildout and just do FTTH. And they did, though not with
symmetric gigabit speeds, because reasons (bla bla customer demand, costs,
etc..) The highest speed is 1000/400 Mbps for $120/mo. (which is super
expensive compared to what was promised by the Chinese and also compared to
general purchasing power in the country).

~~~
wu_187
ive got 1000/1000 unmetered in the US for ~$110/month

~~~
milankragujevic
Well.... yes, you do, and some people in the US have 4/0.5 Mbps for the same
price. It really depends.

For example, in Niš, which is the most developed city when considering
internet infrastructure and the number of ISPs, you could have 600/400 Mbps
for $10/mo with ~300 TV channels on unlimited* TVs. You'd even get a [VoIP]
landline.

* all the TVs in your home, basically up to 5 for 99% of users

Then Telekom Srbija got the Chinese money and bought 10 largest ISPs other
than them and SBB (the other side of the duopoly), and now there's 200/20 Mbps
on FTTH for $30/mo on up to 3 TVs with 260 channels and a landline that has
call routing problems. Users which sign new contracts are downgraded and pay
more, those that don't sign new contracts suffer with TV and Internet dying,
and are told to "sign or sue us".

Ironically, I chose the second option, and won
([https://news.ycombinator.com/item?id=21733553](https://news.ycombinator.com/item?id=21733553))
but the thing I "won" is free contract termination and being repaid fees that
were charged but are not mentioned or required under the TOS and Contract at
the date of signing (given I have not signed anything else giving permission
or agreeing to anything new, and they didn't officially force new contracts on
people so that people can't cancel to run away)...

------
zw123456
Fiber 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
Directional couplers are a thing. Thomas Edison patented multiplexing
techniques for telegraph wires that didn't even need them.

~~~
jrockway
I 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.

~~~
Dylan16807
> The biggest problem I've found is that the Internet isn't really ready for
> customers that can download at 10Gbps.

TCP is dumb and if it can saturate your connection it will increase your
latency. I feel like being unable to saturate a connection is a _good_ thing.

There are other measures you can take to avoid saturation, but simply having
an oversized pipe is hard to beat.

~~~
jrockway
This may be relevant to your interests:
[https://apenwarr.ca/log/?m=201808](https://apenwarr.ca/log/?m=201808)

~~~
Dylan16807
But to really get best results, you need that management on both sides of a
chokepoint, and you still want every other link in the system to be oversized.

Fast links are a simple solution to a lot.

------
electriclove
I 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.

~~~
cma
Seems more likely they want price discrimination for their business offerings.
I don’t know how well that would explain things in competitive market areas
though, but in monopoly areas it would make sense.

~~~
leetcrew
I always assumed this was part of it. ISPs want you to have to pay more if
you're going to be hosting a server (and possibly making money). also explains
why port 80 is usually blocked.

~~~
anticensor
You cannot block port 80 like you imagined. The web would not function
normally. HTTP uses port 80 both for data and control.

~~~
MertsA
It's extremely common for ISPs to block inbound packets with a destination
port of 80, 443, 25, etc. Of course they don't block them outgoing (with the
exception of port 25 commonly). He didn't "imagine" anything and it's quite
out of form on HN to claim something like that.

~~~
anticensor
Port 25 is SMTP, it needs to be allowed in outgoing direction. Otherwise you
will be locked to proprietary web mail.

~~~
namibj
There's a dedicated SMTP submission port. Try dialing e.g. gmail's MX record
on 25. It might/should probably block.

~~~
anticensor
If you mean port 465, it is the port for SMTPS, not a dedicated submission
port.

I received timeout, not block, when I queried gmail on port 25. If it were
blocked, I would get a TCP reset.

~~~
vidarh
Port 587.

Not nearly all consumer isps block port 25, but a lot do.

------
rocqua
Besides 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.

~~~
sathackr
Both 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

~~~
supertrope
Full duplex DOCSIS 3.1 has theoretical maximums of 10Gbps down and up. It
relies on precise timing and echo cancellation to allow the cable modem and
CMTS to transmit simultaneously on the same frequency bands. Kind of like how
gigabit Ethernet allows both ends to transmit simultaneously on the same four
pairs.

~~~
dfox
The question is how practical that mode of operation is on real network, or in
other words whether it actually makes sense to run DOCSIS on network that can
reliably support that mode (think various xDSL technologies that can push
>1Gbps over <100m of what essentially is Cat5 cable)

DOCSIS is somewhat inherently asymmetric due to nature of the CaTV network.
Even if the upstream and downstream channels would have same bandwidth, the
upstream direction tends to have significantly worse SNR. Historically this
was caused by splitters along the way, but also the cable modem is relatively
cheap device installed on customer premises and thus has inherently lower
transmit power and worse SNR than CMTS. This is the main reason why CMTS
tend(ed) to have more upstream receivers than downstream transmitters.

------
the_mitsuhiko
That 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.

~~~
lawnchair_larry
The reply was actually pretty spot on. It’s not a demand issue. It’s true that
there is not overwhelming demand for higher upload, but that’s pretty far down
the list of what prevents it from being offered.

DOCSIS 3.1 allows it on paper, yes. But in the real world, bandwidth is a huge
constraint, especially if you’re also serving digital cable. No cable ISP in
North America today on D3.1 has a network that can support it even if they
wanted to.

For example, Comcast has 4 upstream 6mhz sc-qam channels (which is basically
using none of the advantages offered by 3.1) and 32 downstream, and their
video service is 720p across the board and overly compressed. They are
constantly trying to free up data channels and migrate to newer codecs, and
eventually go to IPTV, but that requires changing hardware both in their
network in the customer’s home, or the customer’s TV goes black and their
internet goes out and you get to hear their rage when you tell them they have
to spend a few hundred dollars on new cable boxes/modems so that Comcast can
build out their network. It’s a massive infrastructure upgrade to use DOCSIS
3.1 to its full potential that is further complicated by a need to support all
of the legacy hardware during a transition.

Add to the mix that upstream channels are far more susceptible to unwanted
ingress, most homes are full of amateur RG59 coax cable, and it becomes a
support/troubleshooting nightmare as well. When you get into higher upstream
speeds, these deficiencies become a much bigger problem.

I have observed speed tests on an uncapped docsis 3.1 modem on the comcast
network getting full bandwidth on all channels, and it was still way below
100mbps upstream (around 80mbps).

~~~
mercora
in Germany Vodafone deployed DOCSIS 3.1 partially and while still not
symmetric i get 100Mbit/s down and 50Mbit/s up more or less consistently with
DOCSIS 3.0 where i live unless something goes wrong (it does sometimes
interfere with LTE here). DOCSIS 3.1 is also available with lots of
[0]channels using the newer 1024QAM. they offer up to 1Gbit downstream and
50Mbit upstream for about 70€ a month. i also made a [1]screenshot of the
channel usage and stats page of the modems web interface.

[0]
[https://helpdesk.vodafonekabelforum.de/sendb/belegung-11.htm...](https://helpdesk.vodafonekabelforum.de/sendb/belegung-11.html)

[1]
[https://gist.github.com/mercora/ef66f5bcd95b060ac25269b17cc6...](https://gist.github.com/mercora/ef66f5bcd95b060ac25269b17cc66b75)

~~~
iamzenitraM
It's not required to have DOCSIS 3.1 to have 100Mbit/s symmetry, 3.0 can
provide that. Vodafone in Spain has a mixture of HFC footprint (the widest),
its own small FTTH footprint, and Telefonica (Spain's DTAG) wholesale FTTH.
Prices and speeds for the three of them are the same, but if you are on an
FTTH zone you get symmetric upload speeds, while on HFC zones they provide
100Mbit/s upload with all their plans (min download is also 100MBit/s).

They argue they will be able to have symmetry on 1Gbit on HFC when they
complete their DOCSIS 3.1 rollout, but that has been going on for years with
no news. Ironically their own FTTH footprint is pretty small so they end up,
in most cases, providing better upload speeds when reselling Telefonica
infrastructure than with their own.

------
kazinator
> _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
Mostly 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
> _Mostly true._

Where lies the falsehood?

------
vkdelta
Because 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

------
3fe9a03ccd14ca5
1 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.

------
pwarner
I 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.

------
z3ro
I 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.

------
shmerl
Because 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.

------
charwalker
I 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.

------
Hamuko
My ISP will not sell me anything better than 1G/100M on fiber. Maybe if I
looked into business plans maybe.

------
in3d
A 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.

------
magoon
Not mentioned, they don’t want to support residential customers serving web
sites (or anything else)

------
R0BERTGLICK
That was an interesting article thanks for sharing.

------
parski
Is bandwidth speed?

