Gigabit Fiber Ludicrous Speed (990mbps+)

Internet access discussion, including Fusion, IP Broadband, and Gigabit Fiber!
3 posts Page 1 of 1
by johnboiles » Tue Feb 05, 2019 7:00 pm
I'm extremely happy with my Gigabit Fiber. I consistently get 940mbps symmetric on speed tests when I'm the only one using the network. Using iperf3, I'm able to see about the same speed between wired computers on my network which indicates to me that 940mbps is about the highest data transmission rate I'm able to achieve over ethernet. This makes reasonable sense because of the packet overhead for TCP networking limits gigabit ethernet under normal conditions limits data transmission to around that speed (see also: a good article with the math). Everything is functioning as it should at its max speed.

All of this is great, and I am very happy with 940mbps, but I have been curious about something for a while. What follows should be viewed as an academic exercise to understand how things work.

When the Sonic technician (Don Pierson -- he was great!) came for the first time, I looked over his shoulder as he ran a test against the FastMetrics Inc. server from his Dell Windows laptop. He was able to achieve 994.32mbps down! I've been reading about MTU and jumbo frames, and it seems like the only way to transmit data that quickly over a gigabit ethernet connection is by enabling 'jumbo frames' (MTU: 9000). This means every packet includes up to 9000 bytes of data per packet (instead of the default 1500), thus minimizing the packet framing overhead. Experimentally on my local network, when I enable jumbo frames, I'm able to get iperf3 scores of 990mbps between computers on my network.

This all suggests to me that somehow, the Sonic technician was receiving jumbo frames from the fiber modem (optical network terminal - ONT). Or possibly somehow he was using ipv6 (though in my understanding that's not yet enabled for fiber customers). I've tried enabling jumbo frames on my computer and plugging straight into the ONT. I've also tried then restarting the ONT in hopes that maybe it does some kind of path MTU discovery at startup to determine the MTU. However my speed tests still top out at 940mbps and running `ping -D -s 8972 GATEWAYIP` using the IP of the gateway I'm getting from DHCP shows that I'm not able to send packets to the gateway larger than MTU~2000. I'm a bit stumped (and very curious) as to how that technician was able to achieve 994mbps down! if anyone had any information or explanation I'd be very excited to hear it!


by christophermjennings » Thu Feb 07, 2019 5:28 pm
Can I ask where you're located that you're getting that "holy grail" speed rating? I think the fastest I've seen at my place in the Rockridge neighborhood of Oakland is 400 down/up.
by dane » Thu Feb 07, 2019 5:47 pm
I'm a bit skeptical about this number, and I wonder if there are measurement or compression artifacts that are skewing the result. For a full 1Gbps Ethernet connection, with TCP and IP overhead, I'd expect a maximum payload speed of about 940Mbps.

For the member seeing ~400Mbps - that'd be some sort of bottleneck in your LAN, cabling, PC, antivirus software, etc. To achieve full speed, you need a reasonably modern Gigabit Ethernet equipped PC connected to the Sonic router with a Cat5e or better cable.

We've seen very slow speeds on PCs with older browsers, and in some speed tests with some java versions. The way to diagnose that is to use a native speed testing application:

We've seen slow speeds on PCs running antivirus software, because the CPU has to examine all of the traffic - this can be a huge performance impact. Disable that to test if it's a factor.

We've seen slow speeds on devices behind 100Mbps Ethernet switches. Simple, but sometimes someone has forgotten that somewhere in their local network they've got an old switch that isn't Gigabit capable.

We've seen slow speeds on laptops connected to Ethernet with USB-connected dongles. Even newer USB doesn't do full Gigabit, you've got to get to Thunderbolt adapters before you'll see full speed - and some older laptops don't have any external interface that'll do the full speed.

We have also seen consumers with inexpensive Ethernet cords that are 100Mbps only - because they've only got four wires instead of the proper eight! Yep, using an old cable that you got for free with a consumer electronics device a decade ago may not allow for top speed. :lol:

Oh, and for those who've got their own WiFi routers, extenders, repeaters, powerline equipment, etc - all can be sources of slow performance. (Consider instead a whole-home mesh WiFi solution from Sonic!)

What's wonderful about Gigabit fiber to the home is that the connection to our network is no longer the bottleneck. That's never been the case before, with copper services from DSL to cable, the connection was always slower than the devices or the LAN - and the WiFi.

The result today is that in virtually every case, any time you're not seeing 900+Mbps of payload delivery on your client devices, that issue is something you can totally resolve in the home, with the right equipment and connection type - Gigabit switches, Cat5e Ethernet cabling, etc.

And, in case it's not clear: WiFi doesn't deliver full gigabit speed to mobile devices today. Despite all of the "1300" and "1600" claims of crazy antenna-studded 802.11ac (WiFi 5) devices, these are aggregate numbers: upload plus download, and multiple ideal clients each with multiple antennas themselves. Someday WiFi might begin to catch up with our fiber.. Meanwhile, put high-demand non-mobile devices on Ethernet if you can, it's faster and more reliable. 8-)
Dane Jasper
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