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Author Topic: 2.5Gbps Ethernet - why?  (Read 783 times)

snadge

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2.5Gbps Ethernet - why?
« on: November 23, 2021, 10:55:01 AM »

Hi Guys and Gals  :)

I have found new computers with 2.5Gbps Ethernet ports, can anybody explain this strange speed? (usually factors of 10/100/1000/10,000) - As I learned on my other thread that BT uses 2.5Gbps on the backhaul for every 32 customers on FTTP, now I saw a program that said they can now use different 'wavelengths' sent at the same time (multiplexed), where each 'wavelength' could be used for each customer. Am I right in thinking they already use that technology just to get the 2.5Gbps bandwidth? - just I wondered if these 2.5Gbps NIC's were put in place ready for when the time comes that different wavelengths are used and we may be able to draw 2Gbps each?

again this is just me thinking out loud, and not saying anything in concrete.

It is probably just for those who get slightly over 1Gbit, in which a faster than 1Gbit NIC & Router is needed, as I've seen some in London offering 1100Mbps down and 100Mbps up..?

I thought it was pretty smart on BT's side to choose that magic 900 number - due to most devices with LAN's now are 1Gbit, and achieve 94-95% of the bandwidth after overheads - so 940Mbps MAX on a 1Gbit NIC  -well done BT, when you have other FTTP ISPs selling services that require 2.5Gbps/10Gbps NICs and Routers. 2.5Gbit NIC must be cheaper to make than 10Gbit NIC.

cheers
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Weaver

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Re: 2.5Gbps Ethernet - why?
« Reply #1 on: November 23, 2021, 01:39:54 PM »

No, there are two new(ish) standards for ethernet over copper at 2.5 and 5 Gbps. These work iirc over existing cabling over modest lengths, I think, again, canít remember. This has been an opportunity for mfrs such as Cisco to make WAPs with 2.5 Gbps or 5Gbps copper ports on them instead of requiring bonded dual 1Gbps links as they were doing. This is because some of the high end business WAPs have become embarrassingly fast, with for example dual radios (like my old ZyXEL).
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j0hn

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Re: 2.5Gbps Ethernet - why?
« Reply #2 on: November 23, 2021, 04:29:44 PM »

Quote
As I learned on my other thread that BT uses 2.5Gbps on the backhaul for every 32 customers on FTTP, now I saw a program that said they can now use different 'wavelengths' sent at the same time (multiplexed), where each 'wavelength' could be used for each customer. Am I right in thinking they already use that technology just to get the 2.5Gbps bandwidth? - just I wondered if these 2.5Gbps NIC's were put in place ready for when the time comes that different wavelengths are used and we may be able to draw 2Gbps each?

GPON has 2.5Gb/s down and 1.25Gb/s up shared between everyone on a splitter. That's a single OLT port, shared between up to 32 customers (Openreach usually cap this at 30 customers).

Openreach can also run XGS-PON over the same fibre.
XGS-PON is 10Gb/s down and 10Gb/s up.
So in the future Openreach can run the 2 different PON technologies on the same fibre.

That means they could sell a single customer 10Gb/s symmetrical without it affecting the GPON bandwidth of the other 29 users.

There's very very little XGS-PON live on the Openreach network. Only a few lines from a single trial.

That's somewhat different/unrelated to 2.5Gb/s NIC's.
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Alex Atkin UK

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Re: 2.5Gbps Ethernet - why?
« Reply #3 on: November 23, 2021, 06:25:15 PM »

Quote
NBASE-T technology supports rates greater than 1 Gb/s that are needed by advanced wireless technologies such as 802.11ac.
The introduction of protocols that provide higher data transmission rates is often associated with new categories of cabling, however NBASE-T specifies two new data transmission rates of 2.5 Gb/s
and 5 Gb/s that will take advantage of much of the installed base of Category 5e and Category 6 cabling at lengths of up to 100m.

https://archive.nbaset.ethernetalliance.org/wp-content/uploads/2016/08/NBT_CablingWhitePaper_082916.pdf

So basically, it was about solving the problem of NOT having to upgrade cabling to get higher speeds.

There are also other issues such as 10Gbit transceivers need a lot more power so can't be made into USB devices, not a problem for NBASE-T.
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Reformed

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Re: 2.5Gbps Ethernet - why?
« Reply #4 on: November 24, 2021, 12:24:10 AM »

Hello.

The 2.5 Gb is the speed that hits your ONT.

The OLT on the other side of the fibre knows which service level you've purchased so throttles your download and upload to the correct level.

Your ONT receives all the downstream traffic for everyone on the split but cannot decrypt the traffic intended for others and will discard anything not addressed to you anyway.

The OLT will only send a maximum of the 1G you're subscribed to in data addressed to your ONT per second.

The ONTs receive permission from the OLT to send data upstream, so the OLT will give your ONT enough time on the upstream to send 115 Mb/s and no more.

The capacity is split between all the GPON devices in timeslots. Time Division Multiplexed Access.

The OLTs have both 10G and 1G optical connections to service providers. No copper for anything besides a management port.
« Last Edit: November 24, 2021, 12:27:54 AM by Reformed »
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Reformed

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Re: 2.5Gbps Ethernet - why?
« Reply #5 on: November 24, 2021, 12:41:26 AM »

On the strange Ethernet speeds the copper carries RF, radio frequencies, just as ADSL and VDSL do. The older cabling isn't certified to handle 10 Gbit over 100 meters due to the bigger RF spectrum / broader frequency range needed to carry the data. VDSL went up to 17 MHz, G.fast 106. 10 Gbit needs 500 MHz with crosstalk mitigation that existing cable didn't have.

2.5G fits into 4 pairs at 100 MHz - the rated capacity of Cat 5e.
5G fits into the 4 pairs at 200 MHz - the rated capacity of Cat 6.

If you have a look at WiFi speeds you'll note that the 2.5G and 5G speeds seem a good match for access points, and you'd be right. They are a big driver alongside datacentre, however I'm seeing a ton of use of SFP+ NICS and switch ports so a combination of top of the rack aggregation, some of it over DACS or fibre when more than gigabit is required seems to be the sweet spot.
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Chrysalis

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Re: 2.5Gbps Ethernet - why?
« Reply #6 on: November 24, 2021, 05:15:06 PM »

I think its market segmentation, they dont want people using consumer boards in datacentres and the like, so try to not match as many features as possible.

2.5 is probably enough for people to be happy on gigabit internet services, NAS connectivity etc. Consumer use cases.

Kind of like why we use m.2 instead of u.2 for NVME drives.
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Ronski

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Re: 2.5Gbps Ethernet - why?
« Reply #7 on: November 24, 2021, 07:54:27 PM »

I think also 10Gb was very expensive, so 2.5Gb and 5Gb was brought in as a cheaper option (but not by much), I doubt it has very little, if anything to do with broadband speeds. My server board actually has 2.5Gbe, but I'm using a 10Gb SFP+ card and fibre back to the switch.

I run my network here between my main PC's at 10Gb, using good quality CAT5E that I installed over the last 19 years. On good quality cable it should work up to about 30 meters or so, longest length I've run it over was 25 meters, plus 3 patch cables, so getting on for 28 meters. This was the two sockets in my office, linked at the patch panel.
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Alex Atkin UK

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Re: 2.5Gbps Ethernet - why?
« Reply #8 on: November 24, 2021, 08:07:09 PM »

I think also 10Gb was very expensive, so 2.5Gb and 5Gb was brought in as a cheaper option (but not by much)

I wouldn't say not by much.

Typical retail price for a 2.5Gbit card is about £20,  typical price for 10Gbit is £97.
Yes you can find them cheaper used or by looking hard, but you also have to consider most of those are PCI 2.0 x8 cards when anyone with a GPU need PCIe 3.0 x4 or x1 to avoid throttling their GPU slot.

Also an 8 port 2.5Gbit unmanaged switch costs around £160, an 8 port unmanaged 10Gbit costs £310.

So upgrading all 8 clients to 2.5Gbit including the switch costs £10 more than the 10Gbit switch alone.

2.5Gbit total £320
10Gbit  total £1086
« Last Edit: November 24, 2021, 08:09:53 PM by Alex Atkin UK »
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Chrysalis

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Re: 2.5Gbps Ethernet - why?
« Reply #9 on: November 24, 2021, 09:41:01 PM »

Funny enough I feel still happy with a 1gbit LAN.  If 2.5gbit was only slightly more expensive I would upgrade but those switch prices are too unattractive for me, even 1gbit NAS access is ok for me.
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snadge

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Re: 2.5Gbps Ethernet - why?
« Reply #10 on: November 24, 2021, 11:13:49 PM »

Yes, it's all interesting stuff, I'm liking what's possible coming in the future with all the new tech mentioned in the previous posts (and learning it all I enjoy!), and what i saw with the multi-coloured 'wavelength spread' over the EMI as 'one per user' - or it's its probably old news and been drawn into gathering the spec we get now instead! The one I was watching was about the tech that may be being used in the undersea cable, that was 100,000Gbps or something like that - it may have been used for that only, but it was a great watch! I can't remember the name. I've seen a ton of videos!

but I feel a bit for Weaver who has to wait Five bloody years for FTTP in his current situation, doesn't he fall under B4RN? - I feel his/hers/their pain, 3 bonded lines for 2.5Mbps! it does make you realise how lucky you/we are, because I'm also single, on my own, so all the bandwidth is mine, and I understand that most of you have families on Wi-Fi (mobiles & IoT) and gaming on LAN, and so when the bandwidth hits the router it is shared amongst them too, so I know some of you on this forum could even have working connections even at fairly average speed brought to a halt!!! I've seen it happen at BOTH my sisters & many others. I fixed one, only to 3-4Mbps ADSL from 256Kbps on Talk Talk by removing the ring wire (a long time ago, and a long cable from the exchange, 5km or over I'm sure). The other sister i sorted by telling her she needs to up her bandwidth from 4Mbps using ADSL and get on Plusnet VDSL 40/10 (which she did and sorted it all).

Yes it makes one think!
« Last Edit: November 24, 2021, 11:21:06 PM by snadge »
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Weaver

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Re: 2.5Gbps Ethernet - why?
« Reply #11 on: November 25, 2021, 12:33:53 AM »

Clarification, itís 7.5 / 1.2 Mbps. (Upstream combined figure should be better than that even, but some speed testers only report 0.9 Mbps combined, which is to do with out-of-order packet delivery or apparent jitter, or something. Canít understand it, as the Firebricks are fundamentally broken, since the FB6000 units at AAís end achieve highly efficient downstream combined figures, itís just upstream ie my FB2900, not AAsí.)
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snadge

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Re: 2.5Gbps Ethernet - why?
« Reply #12 on: November 25, 2021, 12:42:46 AM »

Clarification, itís 7.5 / 1.2 Mbps. (Upstream combined figure should be better than that even, but some speed testers only report 0.9 Mbps combined, which is to do with out-of-order packet delivery or apparent jitter, or something. Canít understand it, as the Firebricks are fundamentally broken, since the FB6000 units at AAís end achieve highly efficient downstream combined figures, itís just upstream ie my FB2900, not AAsí.)

Well, from what I know from HDMI signalling, it could be due to the sheer length of the pair, causing 'out-of-time' packets (possibly even in the legs somewhere along the route, made worse), or most likely dropped (also) and a high CRC count has given? am I right?

Am I also right in saying is it the Firebrick alone that handles the 'load-balancing' too?
« Last Edit: November 25, 2021, 12:45:01 AM by snadge »
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Weaver

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Re: 2.5Gbps Ethernet - why?
« Reply #13 on: November 25, 2021, 12:48:04 AM »

There are Firebricks at both ends, my end and at AA. They handle the bonding, where all IP traffic, even one single active TCP connectionís traffic is split up so that itís triple speed; and my Firebrick handleís the upstream, AAís handle the downstream. Some people use the term load-balancing to mean a situation where you have to have multiple users or multiple TCP connections active to see the benefit.
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snadge

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Re: 2.5Gbps Ethernet - why?
« Reply #14 on: November 25, 2021, 01:07:34 AM »

There are Firebricks at both ends, my end and at AA. They handle the bonding, where all IP traffic, even one single active TCP connectionís traffic is split up so that itís triple speed; and my Firebrick handleís the upstream, AAís handle the downstream. Some people use the term load-balancing to mean a situation where you have to have multiple users or multiple TCP connections active to see the benefit.

Makes sense at such speeds if TCP is used in that manner for much lower speeds
- load-balancing would be like one of our fellow Kitzens 'triple header' (2x900 + 1x500 = 2300Mbps on Openreach) - ha in fact I've just made a connect, he probably KNEW that it was a 2500Mbps on the backhaul, and probably was first on his pod and decided to suck it dry haha - brill

a punch in the gut to you, sorry  :-\
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