SFP+ DAC VS Fiber Latency: Copper Is Quicker Than Fiber



Amazon Affiliate Retailer
➡️

Gear we used on Equipment (affiliate Hyperlinks)
➡️

Strive ITProTV freed from cost and get 30% off!
➡️

Use OfferCode LTSERVICES to get 10% off your order at
➡️

Tesla Referral Program Supply
🚘

Lawrence Programs Shirts and Swag
👕

Digital Ocean Supply Code
➡️

HostiFi UniFi Cloud Internet hosting Service
➡️

Shield you privateness with a VPN from Personal Web Entry
➡️

Google Fi Service Referla Code
📱

Extra Of Our Associates that assist us out and may get you reductions!
➡️

Twitter
🐦

Patreon
🔗

Our Boards
🔗

Our Net Website
🔗

SFP+ 10 Gigabit Connectors: LC Multi-Mode Fiber, 10GBASE-T, and DAC Cables.

source

Comments (37)
April 5, 2020

What will be the latency difference if 10G SFP+ fiber vs DAC?

  • April 5, 2020

    Question: are SPF+ transceivers compatible with each other? or they need to be always the same brand? (example, buy a HP 10Gbe SPF+ nic card , can you mix them with a microtik SPF+ transceiver?)

    April 5, 2020

    Correction: Information travels with lightspeed in fiber AND copper. It is EMWaves either way!

    April 5, 2020

    Question:

    Can you give me a real world scenario where a ~0.000005ms different would make a difference or potentially be a problem? I know in the consumer space there's no way there would be a distinguishable difference, but what about in the enterprise space? I always knew DAC was faster than fiber in terms of latency at the module, but didn't know the numbers were in the nano second range. Crazy.

    April 5, 2020

    1:061:15
    I don't suppose there'd be a way to measure exactly how much latency it adds? I'm working on something where using an SFP+ to 10Gbase-T module like that may be my only option.
    Long as it's sub-millisecond I'm good, and I know that's not a very high bar to reach, but there doesn't seem to be a lot of info out there about it and I'd rather have a pretty clear answer before investing a few hundred bucks on some gear that may not even suit my needs.

    Thanks for these videos, btw. Very educational.

    April 5, 2020

    1. With DAC cables you are limited to 7m and it depends on the switch you can be even limited to 3m, been there and seen the problems
    2. DAC cables you are limited to compatibility between venders, not so much with Fibre as you can use different SFP transceivers at each end
    3. Distance, even at home I have 20meter fibre cables with SFP+ transceivers for about £100 pound per run total cost between HP switches.
    4. No EMI issues, with Copper you'd need shielded ethernet cables

    April 5, 2020

    I know you just did a video on the differences between media types, but it bares repeating for those who just stubble across this vid. and are reading comments. The Copper SFP+ to RJ45 modules are not discussed here, and in terms of power draw and latency in early 2020 it's a bit… Well I wouldn't want to have more than a couple of those modules in a microtik 4 port. They get pretty warm and … physics. As far as the subject of this video, latency I think they might be a bit worse then DAC.. not sure where they place when compared to fiber though. I expect this to change with better power efficient / less latency modules going forward into the decade.

    April 5, 2020

    Fiber is not light speed. It's still light moving in a glass medium. (less than speed of light).

    April 5, 2020

    ofc its faster, 0.95c vs 0.7c (c=speed of light)

    April 5, 2020

    The speed of light inside of glass is actually 2/3 of the speed of light. While signals inside copper can propagate at anything between 50-95%, and radio waves 90-99%.

    April 5, 2020

    But fiber allows for much greater range. Also cheaper when compared to purchasing X540 cards for each blade.

    April 5, 2020

    I do have a Mikrotik switch running SFP+ and OM3 fiber, running to my 2 servers in my basement, from my home office/lab. I like the 10 gig transfers, and latency doesn't seem to be an issue over 20 meters. I did notice that the 1 gig POE from the Mikrotik to my TP-Link switch slows down my gigabit internet 100-200 megabits into my PC connected to it (the Mikrotik). Other computers not connected through the Mikrotik, get full bandwidth from their connection to the TP-Link switch, which is also connected directly to my router. (1 gig)

    April 5, 2020

    The main advantages of Direct Attached Copper is generally that it needs no expensive optical conversions.
    Nor does it need a relatively expensive fiber. But can instead rely on a simple yet effective pair of copper wires surrounded by a foil shield.

    But honestly, the main reason copper is faster than light, is due to the fact that the light in an optical fiber isn't even traveling close to the speed of light in vacuum.
    A coaxial/twinaxial cable, can reach speeds closer to the speed of light in vacuum far more trivially than what a strand of glass is able to. Mostly since one can use materials that have a lower relative permittivity than that of glass.

    Also, all optical sensors and lasers have their own response times as well, adding additional latency regardless of cable length.

    Now, a signal in the electrical domain will also need a transceiver, since the LVDS signal from the SFP port isn't really ideal for just sending over a twinax…. So some impedance matching will be in order, but that is usually not that hard. (It does add latency, but it isn't like the LVDS signal were ideal for driving a laser to start with either, so similar tech will be needed for fiber too….)

    Also, the velocity factor of a typical optical fiber is around 0.65 to 0.8
    While the velocity factor of a typical coax/twinax is around 0.8 and up. (Some coaxial cables are above 0.98, while other types of coaxes have VF as low as 0.4, but they are optimized for other applications where latency obviously isn't important.)

    Though, the main advantage of DAC over fiber is the simple fact that lasers wants a fair bit more power, and are more temperature sensitive compared to a handful of transistors doing impedance matching and signal boosting.

    Also, it would be fairly trivial for a DAC cable to have an amplifier along its length to bring its abilities to even longer lengths.

    April 5, 2020

    I asked around for suggestions of for applications where nanosecond latency on short cables could matter. I received the suggestion high frequency trading where first to respond wins, implemented on an instant response FPGA. But you really need direct to attachment between endpoints or cut-through-switching to ensure you aren’t getting stuck in the much more “slow” store-and-forward switching if you are competing about a few ns.

    April 5, 2020

    @04:25 What the hell? What SFP's did they use?
    and what testing methods, we have access latency of 1.3ms at 7 kilometres with OS2
    I suppose if you pay 20 buck for a cheap Chinese sfp module like g10tek or the like, anything is possible 🙂

    April 5, 2020

    protocol is a factor… i work with mellanox infiniband switches that provide sub-ms latency for large HPC clusters.

    April 5, 2020

    Fiber is so cheap these days I see no reason to buy DAC's as a reason to "save money". They're harder to route and in this day and age have no real benefits. Optics can also be used with any length of fiber and are easier to route. Fiber really isn't that delicate. If you're really worried about it you can buy armored cables for about 15% more than normal cables 😉

    April 5, 2020

    latency != speed.

    April 5, 2020

    Have you performed analysis of real world impact on short cables, where does it actually matter? These ns delays are similar to necessary delays such as the inter packet gap in most networking protocols, which rarely are huge culprits to total delay. And a store-and-forward switch would add much more delay than the cable delay. So I have some doubts about a few ns latency mattering in applications except supercomputing interconnects. The entire stack would need to be low latency optimized and latency constrained for a few ns to matter. I’d imagine most applications unable to demonstrate any performance impact due to cable latency on a short cable.

    April 5, 2020

    I use copper DAC for ISL, Single Mode OM4 for almost everything else.

    April 5, 2020

    Wow the timing on this video! I just recently got into 10Gb networking and currently have fiber installed on my home lab, I was wondering about what had the lowest latency when compared to DAC cables and then this video shows up on my YouTube home page. Thank you for the information!

    April 5, 2020

    So in my rack to connect on my 10 gigs switches together I use 1 meter fiber cables multimode and ubiquiti transceivers so I should probably switch all those over to direct attach copper ? Are there any good right angle direct attach copper patch cables ? the only reason I didn't use direct attach copper is because it's harder to make look clean and my teenie brain thought fiber faster lol

    April 5, 2020

    an idea for your next project. rgb lan cables and if you can control the lights in them you get even more kudos for doing that

    April 5, 2020

    A fiber connection also has more points-of-failure, since the transceivers can go bad and also fiber lines are kinda sensitive when it comes to bending them (unintentionally of course). If there is no need for very high transmission speeds, long distances or electrical separation, copper is the way to go

    April 5, 2020

    Wow so DAC has less latency than having transceivers?! Who would have thought? haha
    No seriously, is anybody surprised about this?

    April 5, 2020

    where is the link

    April 5, 2020

    Interesting as copper is always cheaper to get than fiber (2020).
    But in the end, we're talking about a few nanoseconds of difference (<100ns – remember when 70ns 1 MB SIMMs RAM sticks were considered fast in the 90s). It takes 1000 ns for 1 ms, so with the measured difference we could say they all equal for any sizes since they are less than 100 ns. It will also be overshadowed by any other computing going on in any transfer.

    April 5, 2020

    Could you make a video about the differences and benefits of PON vs SFP vs SFP+ (fiber) and why ISP's usually use PON for fiber connections to consumers.

    April 5, 2020

    My only reason using fiber is just for distance

    April 5, 2020

    That is showing a few ns difference. Typical ping times between two computers connected via direct DAC/fiber/cat6 cables is 0.2-0.5 ms. Saving 2 ns out of 200000 ns is not going to be noticeable.

    April 5, 2020

    The use case for fiber in military labs is that you can run unclassified, secret, and top secret networks in the same cable troughs. You can have multiple classifications at an users desk, and not worry about distance between cables. Copper being a radiant insecure media, while fiber is the most secure.

    April 5, 2020

    Thank you so much for the video! I would never have imagined that the fiber patch cord was slower than the metallic pair, for me this is something new and something I will share for all my colleagues working with Infrastructure.

    April 5, 2020

    Been saying it for years, DAC > Fiber (Depending on your needs/layout)

    April 5, 2020

    Did I hear that right, electricity through a conductor doesn't travel at the speed of light?

    April 5, 2020

    Very interesting results, I primarily use DAC cables for in my cabinet due to cost, reduced power use and increased robustness. Any idea how it would stack up to 10Gb/s RJ45 latency?

    April 5, 2020

    Do they make a fiber to coax converter? I want to run fiber in my rooms, but want to piggyback off coax lines throughout my home; much like a MoCA adapter, but for fiber.

    April 5, 2020

    We use SFP fiber to get ethernet to areas where long copper would never work due to interference due to proximity to other equipment.

    Leave a comment