Why are FTTP speeds asymmetric?

Is there an inherent technical limitation to why the Openreach FTTP products are all asymmetric?

From what I can see in other parts of the world, FTTP products are often symmetric as standard.

Generally speaking, most internet use is a small upload (the request for specific data) followed but a big download (the requested data being delivered)

This is, of course, an enormous over simplification, but kinda points in the right direction.

In reply to a post by pleasence:

Is there an inherent technical limitation to why the Openreach FTTP products are all asymmetric?

Because they want to be. Their competitors (Hyperoptic, Gigafast etc) are not.
I suspect it makes product comparison easier, but it is strange.

Yes internet access is tradtionally asymetric, but that is changing thanks to mobile devices that record 4K video, and people hosting games at home, and working from home uploading 500 Mb pictures or graphic models etc.

The GPON (ITU G.984) and XG-PON (ITU G.987)standards that Openreach are using are inherently asymmetrical. That said they are both 2:1, that is for example GPON is 2.4Gb/s down 1.2Gbps up shared over all the connected ONT's on an OLT. For XG-Pon it is 10Gb/s down and 2.5Gbps up shared.

As such when Openreach do a 330/50 product they have taken a deliberate decision to cripple the upload speeds. There is no reason why it should not be 330/165. Heck if they had kept to the 4:1 of FTTC it would be a much more attractive 330/80 product. The cynics (myself included) would suggest this is to protect their leased line business by crippling upload speeds.

Edited by jabuzzard (Thu 16-Jan-20 14:30:28)

The PON technology is asymmetrical, and keeping the retail services the same differentiates them from the leased line ethernet products.

In reply to a post by jchamier:

Because they want to be. Their competitors (Hyperoptic, Gigafast etc) are not.
I suspect it makes product comparison easier, but it is strange.

Wrong it is inherent in the standard they are using. I was under the impression that but Hyperoptic and Gigafast also use PON based networks so under contention they will be asymmetric too. You would have to deploy a P2P network like B4RN and some other alt nets or make sure you never oversold your bandwidth (seems highly unlikely) to genuinely be able to offer symmetric speeds with PON. My guess is Gigafast and Hyperoptic oversell their upload speed in the knowledge that most people don't use it so everything is fine till it's not.

Yes internet access is tradtionally asymetric, but that is changing thanks to mobile devices that record 4K video, and people hosting games at home, and working from home uploading 500 Mb pictures or graphic models etc.

Wrong again, domestic internet access has at times been asymmetric but in general internet access has always been symmetric.

Thanks for all the responses on this.

In reply to a post by jabuzzard:

The GPON (ITU G.984) and XG-PON (ITU G.987)standards that Openreach are using are inherently asymmetrical. That said they are both 2:1, that is for example GPON is 2.4Gb/s down 1.2Gbps up shared over all the connected ONT's on an OLT. For XG-Pon it is 10Gb/s down and 2.5Gbps up shared.

As such when Openreach do a 330/50 product they have taken a deliberate decision to cripple the upload speeds. There is no reason why it should not be 330/165. Heck if they had kept to the 4:1 of FTTC it would be a much more attractive 330/80 product. The cynics (myself included) would suggest this is to protect their leased line business by crippling upload speeds.

This is interesting, I didn't know the GPON standard had that 2:1 ratio.

Has there ever been official comment from Openreach or a govt department on this? Seems like a question journalists should be asking when our FTTP services are being claimed as world class, but we artificially limit a 10/1 ratio.

It seems like an important issue as more people work from home. My guess is Openreach are still very much in the mindset that domestic internet is about consumption (Netflix, Youtube etc.) and no home user would ever have need for more than 30mbps up.

Hyperoptic is NOT PON based. They are dedicated circuits to the building and then fibre to the floor and Gigabit Ethernet into each apartment (or GigE from basement if distances are short enough).

Don't forget the GPON split, some UK GPON firms use 32 some go all the way to 128.

In reply to a post by jabuzzard:

Wrong it is inherent in the standard they are using. I was under the impression that but Hyperoptic and Gigafast also use PON based networks so under contention they will be asymmetric too. You would have to deploy a P2P network like B4RN and some other alt nets or make sure you never oversold your bandwidth (seems highly unlikely) to genuinely be able to offer symmetric speeds with PON. My guess is Gigafast and Hyperoptic oversell their upload speed in the knowledge that most people don't use it so everything is fine till it's not.

Thanks. I thought they were all using the same as B4RN.

Wrong again, domestic internet access has at times been asymmetric but in general internet access has always been symmetric.

Colloquial speech on a forum primarily aimed at broadband (aka domestic) access. Dialup was symmetrical until 56k, agreed, and business connections were always symmetric. agreed.

It is a product choice, some UK GPON providers use symmetric, some don't. The same around the rest of the world, so are very much in the same class.

Some providers around world have also done 2 Gbps GPON download in the past too.

The Gig Openreach is set to be 1000 down, 220 up which does not look much of an impediment to working from home, unless you are moving uncompressed HD material around but that needs well over 1 Gigabit anyway.

In reply to a post by MrSaffron:

The Gig Openreach is set to be 1000 down, 220 up

Note: the *current* extremely expensive Gig Openreach product is 1000 down, 220 up. There is also 500/165.

The soon-to-be-launched consumer-oriented products are 1000 down 115 up, and 550 down 75 up.

This might be of interest

Openreach to Trial Symmetric 1Gbps UK FTTP Broadband Speeds

If the trials go well, I don't see why symmetric speeds won't be rolled out to residential/SME FTTP services on the Openreach platform though I suspect only the higher end services (0.5 Gbps & above) will see symmetric speeds. Expect to pay a handsome premium though!

Well I wouldn't mind testing it for them LOL

Peak Speed: 550/550Mbps
Prioritised Rate: 220/220Mbps

Would be the one I would go with, if the price was right.

I would also be happy to pay the £500 fee.

Paul

In reply to a post by pleasence:

Is there an inherent technical limitation to why the Openreach FTTP products are all asymmetric?

From what I can see in other parts of the world, FTTP products are often symmetric as standard.

The stuff already mentioned alongside that Openreach guarantee the upload speed will be as advertised.

The CIR / Committed Information Rate they sell to their customers is the same as the maximum.

https://en.wikipedia.org/wiki/Committed_information_...

You'll note that their customers like BT Consumer guarantee 100 Mb/s on the 160 Mb/s based product and 150 Mb/s on the 330 Mb/s based product, those are based on Openreach prioritised rates, but they sell the upload at exactly maximum.

Business decision on the part of Openreach to not contend the upstream.

In reply to a post by jabuzzard:

Wrong again, domestic internet access has at times been asymmetric but in general internet access has always been symmetric.

End user, whether residential, SME or large enterprise, usage of the Internet is generally asymmetrical. It's obviously balanced by data centres serving the content outbound but access networks human beings connect to the Internet through see asymmetrical trends.

The access network technologies serving us all reflect this. xDSL, cable and nearly all PONs are configured asymmetrically.

As far as proportions go the trend is towards broadband and away from leased lines for many enterprises. Access becoming more asymmetrical but it not being a problem - for the cost of 100 Mb/s of MPLS an enterprise can potentially purchase 20 Mb/s of MPLS, 45 Mb/s of G.fast upload, 35 Mb/s of cable upload, 50 Mb/s of FTTP upload, 19 Mb/s of FTTC upload, combinations of the above and end up with similar uptimes to the 100 Mb/s MPLS and higher performance but asymmetry.

I'd point to the network you work on as an example of this - its ratio is largely inbound, not balanced, even though the connections JISC have to the Internet at large are symmetrical.

I imagine that is what the poster was referring to in their definition of 'Internet access'.

In reply to a post by MrSaffron:

Hyperoptic is NOT PON based. They are dedicated circuits to the building and then fibre to the floor and Gigabit Ethernet into each apartment (or GigE from basement if distances are short enough).

Don't forget the GPON split, some UK GPON firms use 32 some go all the way to 128.

I thought that Hyperoptic had made a big fuss about FTTC being called fibre. In which case using some Cat6a (assuming they are future proofing themselves for 10Gb and are not cheaping out on Cat5e) is rank hypocrisy.

In reply to a post by jchamier:

Thanks. I thought they were all using the same as B4RN.

I have never understood B4RN deployment. They use standard fibre so you have separate up and downstream fibres. Even at the time frame that B4RN started deploying BiDi optics where common place and not much more expensive than a normal SFP. These days even a 1Gbps BiDi SFP is under £10. Would have halved the amount of fibre required and halved the number of splices, for an extra £5 per user in capital costs (which is probably less than the capital cost of the extra fibre and labour costs of the extra splicing) and a lower environmental impact though using less materials.

That said once CWDM-PON is standardized as long as you have kept your splits lower than 9:1 you can build a point to point PON network and go fully symmetric without the expensive lasers that a traditional time division PON network would require on all the upstream ONT's to become symmetrical. Noting that is the reason PON networks are traditionally asymmetric, it's down to cost of the laser in the ONT's.

xDSL doesn't have lasers at the consumer end, but has always been asymmetrical. That suggests to me there is more to it on FTTP than the cost of the laser in the user's ONT. I accept it could be a factor of course.

In reply to a post by jabuzzard:

In reply to a post by jchamier:

Thanks. I thought they were all using the same as B4RN.

I have never understood B4RN deployment. They use standard fibre so you have separate up and downstream fibres. Even at the time frame that B4RN started deploying BiDi optics where common place and not much more expensive than a normal SFP. These days even a 1Gbps BiDi SFP is under £10. Would have halved the amount of fibre required and halved the number of splices, for an extra £5 per user in capital costs (which is probably less than the capital cost of the extra fibre and labour costs of the extra splicing) and a lower environmental impact though using less materials.

That said once CWDM-PON is standardized as long as you have kept your splits lower than 9:1 you can build a point to point PON network and go fully symmetric without the expensive lasers that a traditional time division PON network would require on all the upstream ONT's to become symmetrical. Noting that is the reason PON networks are traditionally asymmetric, it's down to cost of the laser in the ONT's.

B4RN use BiDi / 1000Base-BX and always have...

In reply to a post by RobertoS:

xDSL doesn't have lasers at the consumer end, but has always been asymmetrical. That suggests to me there is more to it on FTTP than the cost of the laser in the user's ONT. I accept it could be a factor of course.

SHDSL is symmetrical, VDSL has symmetrical profiles. A decision was made on how to allocate the limited RF bandwidth.

XGSPON increased cost is a combination of more expensive ONT optics and lower port density on line cards in OLTs.

Thanks Carl .

I should have added, as I did in earlier posts, about referring to consumer (and many SOHO) levels. Let's call them retail ADSL/ADSL2+/VDSL2.

This until very recently when the higher speeds and presumed reliability of consumer/SOHO FTTP started making many leased lines redundant. As is being discussed in the thread. The upstream speeds of these FTTP products often being adequate for businesses.

Basically I think a lot of the asymmetry is down originally to historical user needs and provider bandwidth costs. Technological advances and the resulting associated usage patterns having changed everything.

Underlying provider marketing is only just waking up.

The point was trying to make was that consumer level services have been asymmetric since before the internet existed. Though I have a sneaky deep memory that the old 100 baud and 300 baud teletypes may have been symmetric . The clattering of them connected through an acoustic coupler is still easily and chucklingly remembered.

No worries.

The upstream speeds aren't really a big deal for operators. Even symmetrical networks have a bias towards inbound traffic as far as usage goes. Operators will usually be paying their own providers for whichever of the usages is higher of the two directions.

It's a sales thing now. Just as downstream speeds became Internet-[censored] size measurement it seems as though upstream speeds are the next one.

In reply to a post by RobertoS:

Though I have a sneaky deep memory that the old 100 baud and 300 baud teletypes may have been symmetric . The clattering of them connected through an acoustic coupler is still easily and chucklingly remembered.

You don't have to quite as far back as acoustic couplers. Dialup modems were mostly symmetric, unless it was the viewdata 1200bps 75bps that Prestel (Micronet 800) used on my Prism VTX5000 modem in the 1980s. After that it was 1200/1200, 2400/2400 all the way to 33600/33600.

The first difference was the 56k dialup, which relied on the ISP having a digital connection (e.g. ISDN30 or similar) and so the downstream link was faster than uplink. In MANY cases the uplink was really slow, and forcing a 33600/33600 symmetric was much better for TCP/IP due to the ACK packets.

Hi there. We install a true fibre-to-the-building (FTTB) network. Within your building, we use CAT5e cabling or fibre, depending on its characteristics. Both offer the same throughput at this usage. If you need any further info, feel free to PM us.

In reply to a post by CarlTSpeak:

B4RN use BiDi / 1000Base-BX and always have...

Not according to their early documentation on the their website they didn't. Might have changed very quickly but they started out (or at least planned) to start out with standard fibre optics. There was a whole section about possibly changing to BiDi and using the second core for RFoG TV/Satellite or other options at a later stage.

In reply to a post by jabuzzard:

Not according to their early documentation on the their website they didn't. Might have changed very quickly but they started out (or at least planned) to start out with standard fibre optics. There was a whole section about possibly changing to BiDi and using the second core for RFoG TV/Satellite or other options at a later stage.

https://indico.uknof.org.uk/event/29/contributions/3...

FTTH
� PtP delivery not GPON - (want symmetrical)
� 2 fibres per property � 1000BaseBX on one, other spare

Nope you need a more expensive laser for the higher speeds for the upload where the photodiode for the download is basically the same regardless of the speed. This bumps the cost up, multiply by millions of ONT's and add in that most people download more than upload (especially with streaming) you can save a lot of $$$ by making the system asymmetric. Remember a single OLT laser is serving lots of ONT's so a more expensive transmit laser in the OLT is not such a large financial burden. Basically the faster you can turn the laser on/off the more expensive it gets and to transmit information you basically turn the laser on/off very quickly.

As regards xDSL the asymmetric nature is just down to the best way to split the limited spectrum up to achieve the best experience for the majority of users. For example most people would rather get 80/20 than 50/50 on FTTC, but there is no technical or even cost reason for this, the VDSL modem would be the same in both cases.

With a PON network you use a different wavelength for transmit and receive and even through they are passing down the same fibre there is no interference between the two (well strictly speaking there is but it is not relevant here), so you are not carving up the same limited spectrum between upload and download so the reasons for the asymmetry are different.

I have my doubts that long term PON networks make sense. CWDM-PON might save it's bacon but you end up with more expensive equipment in the customers premises and more expensive equipment in the exchange over a BiDi point to point system. Probably looked a good idea a decade ago, but today given the prices of SFP's not so much. It is also a lot easier to mix and match between vendors than with PON based solutions because it's just plain ethernet. There is no that media convertor does not work with my switch, unlike the that ONT does not work with my OLT in PON land. The cheaper equipment either end also make speed upgrades much cheaper in the long run.

Not saying they are not BiDi now or even before they actually started deployment just that was not their original intention. I have very clear memories of reading some of their early pre rollout documentation when they talked about how it was going to be done and thinking well that's stupid use BiDi and half some of your costs.

In reply to a post by jabuzzard:

I thought that Hyperoptic had made a big fuss about FTTC being called fibre. In which case using some Cat6a (assuming they are future proofing themselves for 10Gb and are not cheaping out on Cat5e) is rank hypocrisy.

On an Openreach FTTP service, your ISP will give you a CAT5e cable to go between your ONT and your router - but that doesn't make it a "non fibre" service.

1000base-T gives you a guaranteed 1Gbps, bidirectional link (up to 100m). There is no "up to" speed, and there is no retraining or dynamic line management - it's fixed rate, and it's the same technology as you use for your LAN.

It's "fibre to the building" that counts.

In reply to a post by jabuzzard:

Not saying they are not BiDi now or even before they actually started deployment just that was not their original intention. I have very clear memories of reading some of their early pre rollout documentation when they talked about how it was going to be done and thinking well that's stupid use BiDi and half some of your costs.

They evidently agreed with you!

Same with my service.

Edited by epyon (Fri 17-Jan-20 18:40:58)

In reply to a post by jabuzzard:

In reply to a post by MrSaffron:

Hyperoptic is NOT PON based. They are dedicated circuits to the building and then fibre to the floor and Gigabit Ethernet into each apartment (or GigE from basement if distances are short enough).

Don't forget the GPON split, some UK GPON firms use 32 some go all the way to 128.

I thought that Hyperoptic had made a big fuss about FTTC being called fibre. In which case using some Cat6a (assuming they are future proofing themselves for 10Gb and are not cheaping out on Cat5e) is rank hypocrisy.

That was Cityfibre I think you'll find, and the high court dismissed their case ISTR

Edited by Davey_H (Sat 18-Jan-20 07:49:59)

In reply to a post by CarlTSpeak:

In reply to a post by jabuzzard:

Wrong again, domestic internet access has at times been asymmetric but in general internet access has always been symmetric.

End user, whether residential, SME or large enterprise, usage of the Internet is generally asymmetrical. It's obviously balanced by data centres serving the content outbound but access networks human beings connect to the Internet through see asymmetrical trends.

The access network technologies serving us all reflect this. xDSL, cable and nearly all PONs are configured asymmetrically.

As far as proportions go the trend is towards broadband and away from leased lines for many enterprises. Access becoming more asymmetrical but it not being a problem - for the cost of 100 Mb/s of MPLS an enterprise can potentially purchase 20 Mb/s of MPLS, 45 Mb/s of G.fast upload, 35 Mb/s of cable upload, 50 Mb/s of FTTP upload, 19 Mb/s of FTTC upload, combinations of the above and end up with similar uptimes to the 100 Mb/s MPLS and higher performance but asymmetry.

I'd point to the network you work on as an example of this - its ratio is largely inbound, not balanced, even though the connections JISC have to the Internet at large are symmetrical.

I imagine that is what the poster was referring to in their definition of 'Internet access'.

Said more adroitly, but essentially what I said as the first reply on Thursday.

https://forums.thinkbroadband.com/fibre/t/4634527-re...

I totally agree, in most cases that is the case, 300:50 is fine for us here, but I wouldn't mind some more upload speed, sure 500:500 is a bit too much and the price wouldn't be worth it for us here, but 300:200 or 300:300 might.

Hell even 300:100 would make a huge difference and it would take 3h, 42m, 40s to upload a total of 167GB of RAW media content like 3D Video cut scenes to be processed on a remote server render farm.

But at the moment 300:50 is fine for our general usage.

But I will wait to see what the final price will end up assuming BT actually start selling that package / product.

It might even be cheaper to just get a second 300:50 line and split the data over the two connections.

Paul

In reply to a post by PaulKirby:

I totally agree, in most cases that is the case, 300:50 is fine for us here, but I wouldn't mind some more upload speed, sure 500:500 is a bit too much and the price wouldn't be worth it for us here, but 300:200 or 300:300 might.

Personally I would take 160/80 over 330/50 any day. By pricing it as they do, I think they are trying to make the more sophisticated users who need more upload speed pay for a higher download speed than they will use (or to take a leased line).

It's not like there is a shortage of capacity in the upload direction. At the PON level it's 2:1, and everywhere else in their network it is 1:1. It's purely for marketing reasons.

The only existing products that come near to a reasonable ratio are 500/165 (very expensive), followed by the basic 80/20. If they kept that 4:1 ratio for higher bands then we'd have a 330/80 product which would be very attractive - to the point that it would significantly dampen demand for the new 550/75 and 1000/115 products shortly to be launched.

At wholesale, 550/75 is only £3.00 per month more expensive than 330/50. Maybe some enterprising ISP could create a 330/75 service by using BRAS rate limiting? But it's probably not worth it for the small addressable market.

I would imagine they will try match virgins up and coming DOCSIS 4.0 speeds which you would imagine to be at least 100mbps.

Edited by epyon (Sun 19-Jan-20 10:06:54)

In reply to a post by epyon:

I would imagine they will try match virgins up and coming DOCSIS 4.0 speeds which you would imagine to be at least 100mbps.

Dont you mean 3.1?

yeah.

In reply to a post by epyon:

I would imagine they will try match virgins up and coming DOCSIS 4.0 speeds which you would imagine to be at least 100mbps.

3.1 is being slowly rolled out now. However 4.0 (just launched, renamed from "3.1 Full Duplex") will be quite costly as it seems to be a major rebuild. It is probably the future, but might take a while to get there.
https://www.cablelabs.com/technologies/docsis-4-0-te...

In reply to a post by CarlTSpeak:

I'd point to the network you work on as an example of this - its ratio is largely inbound, not balanced, even though the connections JISC have to the Internet at large are symmetrical.

Happened to be on my routers making some changes today so I took a peek at what the traffic is like from my "facility" aka the supercomputer at my university. We have downloaded 11.5TB, and uploaded 217TB, on a pair of symmetrical 10Gbps links. Yeah that's asymmetric but not the way you where thinking...

The excess download on Janet is down to undergraduates. Once they all disappear in the holidays the traffic gets much more even if not the other way around

However the point I was making is that historically internet connections at the physical layer have largely been symmetric not asymmetric.

In reply to a post by candlerb:

The only existing products that come near to a reasonable ratio are 500/165 (very expensive), followed by the basic 80/20. If they kept that 4:1 ratio for higher bands then we'd have a 330/80 product which would be very attractive - to the point that it would significantly dampen demand for the new 550/75 and 1000/115 products shortly to be launched.

They could differentiate the higher bands with 500/250 and 1000/500 products. As you said it's 2:1 at the PON level and 1:1 everywhere else. I personally think that keeping the 4:1 ratio and doing 160/40 and 320/80 would have been the reasonable thing to do, and then offer the XG-PON offerings at 2:1.

There is actually another issue with PON technology that is not widely acknowledge. That is it has higher latency than a point to point connection. Basically GPON is time division multiplexed so when you want to transmit it has to wait for your slot to come around. Where as point to point would just transmit immediately.

In reply to a post by jabuzzard:

Basically GPON is time division multiplexed so when you want to transmit it has to wait for your slot to come around.

This is true, but it dynamically allocates more timeslot shares to the busiest transmitters, so in practice you're unlikely to notice. I believe it even measures and compensates for the different round-trip times to each of the subscribers (due to different fibre lengths), to make maximum use of the uplink channel.

In reply to a post by jabuzzard:

There is actually another issue with PON technology that is not widely acknowledge. That is it has higher latency than a point to point connection. Basically GPON is time division multiplexed so when you want to transmit it has to wait for your slot to come around. Where as point to point would just transmit immediately.

That's pretty much a non issue, especially for residential connections.
When compared to previous xDSL connections the latency on GPON will still be better.

Additional latency from TDM / DBA on a PON will be µs not ms.

Yeah not sure that Cat5e was a sensible choice as you are kind of stuck at 2.5Gbps max (assuming you deploy NBaseT) without recabling. Would have made much more sense to use Cat6a and have the option of a full 10Gbps.