Why won't my network run at 1 gig?

Y715UJU · Feb 23, 2014

After recently purchasing a NAS I thought it would be a good idea to upgrade my network to gigabit speeds. Unfortunately after the upgrades I am still only getting speeds of 100meg, but I can't understand why. I am using CAT 5E shielded cable, gigabit switch and all PC's have gigabit network cards. I've got 7 network points in total but I'll just concentrate on the two running to the bedroom to save confusion. One of the cables running to the bedroom was installed years ago, the other was installed last year. The old cable does run at a gigabit, the new cable doesn't (neither do any of the other new connections in the house). Both the cables running to the bedroom are shielded, grounded at the switch and take exactly the same route through the house to the same double faceplate, yet no matter what computer or laptop I plug in, the old cable always runs at a gig and the new cable runs at 100meg. Initially I suspected the cable was to blame, so I made a patch lead using the new cable and plugged my laptop directly into the switch. The new cable patch lead ran at a gigabit, proving that the cable is capable of running at those speeds, but why can't I get a gig in my bedroom?! Needless to say, I have invested in a cable tester and all my wiring seems to be correct. I'm all out of ideas now, can anyone else see what I'm doing wrong?

Thanks in advance

ex_bubblehead · Feb 23, 2014

Check all of your components, either you've got a 100mb/sec device in there somewhere, or one or more cables aren't using all 4 pairs.

VincentP · Feb 23, 2014

A cat5e cable contains eight wires, in four pairs.
100 Base TX (100Mbs) requires two pairs.
1000 Base TX (1000Mbps / 1Gbs) requires four pairs.
The maximum length between two active devices is 100m.
Typical installations allow up to 90m fixed cabling and up to 10m in patch leads.
Desktop gigabit switches won't necessarily be able to support the full 100m specification.

Are all four pairs are wired correctly in both your fixed cabling and patch leads?
How long is the cable run?
100 Base TX is much more tolerant of dodgy cabling.

bill001g · Feb 23, 2014

VincentP :

I will admit to picking nits here but this is the key to understanding the cat 6 mess.

1000base TX only require 2 pair but those 2 pair must be cat 6. Because nobody really wanted to replace all their cable nobody went with this standard. There are a few rare cisco routers that support this.

1000base T is the actual standard everyone uses that uses 4 pair over cat5e or better.

I still don't know why they picked the names like they did

wdmfiber · Feb 23, 2014

Tom's did an article just for you; back in 2009. You'll luv it!
"Dude, where's my bandwidth?"
http://www.tomshardware.com/reviews/gigabit-ethernet-bandwidth,2321.html

It's not your cables... it's the good old spinning hard drive.
But if you have two PC's with fast SSD's on the network, you should be able to transfer between those drives at a few hundred megs.

mbreslin1954 · Feb 24, 2014

It's not necessarily the hard drives. I have a Gbps network in my home, and transferring large video files between computers I usually get between 100 MB/s and 113 MB/s transfer speeds. My task manager shows the network running at between 940 Mbps and 995 Mbps. This is between a 500 GB secondary internal HDD on my PC and the 3 TB HDD in my server PC.

100 Mbps runs out to about 10-11 MB/s disk transfer speed. I can't imagine anyone having an HDD that could not handle more than 11 MB/s. Even a slow laptop HDD can do at least 30 MB/s.

No, if his network is topping out at 100 Mbps on some PCs, it isn't the hard drives, unless he's using 10-year-old laptop hard drives.

VincentP · Feb 24, 2014

bill001g - You are right. I mean't 1000 base-T. His switch will be using 1000 base-T, hence all four pairs are required using Cat5e or Cat6 cable.
wdmfiber - I believe the issue is a network link running at 100Mbs. You can view this as a property of the network link in Windows. This is not the same as actual copy speeds achieved over the network connection.

A 100Mbs network link can transfer up to about 8 MB/s. A 1Gbs link can transfer up to about 80 MB/s. Modern 7200 RPM mechanical hard drives can saturate the 80MB/s capability of 1Gbs ethernet if reading and writing sequentially (simple copy of large files without the drive being used for anything else). Older hard drives available when gigabit ethernet was first available could only manage about 30MB/s.

mbreslin1954 · Feb 24, 2014

As I said, I get from 96 to 113 MB/s from my gigabit network with my WD mechanical hard drives. But then I'm using all Intel NICs and the cable runs are no more than 15 feet. Perhaps that makes a difference.

Someone Somewhere · Feb 24, 2014

I've seen 117MB/s over a decent length cable (probably 15-20m) on whatever is in a current-gen HP Envy to a QNAP NAS.

GbE either works or it doesn't - not like DSL where it just drops the sync rates.

Reterminate the end-points.

VincentP · Feb 24, 2014

100 base TX and 1000 base T ethernet use 4B5B encoding. This means 5 bits are required to send 4 bits of payload.
This would mean a theoretical maximum of 100 MB/s over gigabit ethernet, minus any overhead from the IP protocol and the software transferring the file (Windows file sharing, ftp, etc.)
I think it is more likely that Windows file sharing is reporting inaccurate numbers.

Someone Somewhere · Feb 24, 2014

Actually, you'll find that it's 1000Mb/s after the 8/10 encoding. The base data rate is 1250Mb/s, by memory.

That 117MB/s was from dd (linux block level copy tool), measured in decimal megabytes, and averaged over a 256GB (decimal again) file.

EDIT: Wrote 100 instead of 1000.

VincentP · Feb 25, 2014

Someone Somewhere :

You're right. Symbol rate is 1.25Gbaud to achieve 1Gbps data rate.

Someone Somewhere · Feb 25, 2014

Actually, on further reading I think I might be wrong - that's the case for the fibre-based versions, but 1000baseT (not TX) uses some other encoding method. From Wikipedia:

The IEEE 802.3z standard includes 1000BASE-SX for transmission over multi-mode fiber, 1000BASE-LX for transmission over single-mode fiber, and the nearly obsolete 1000BASE-CX for transmission over shielded balanced copper cabling. These standards use 8b/10b encoding, which inflates the line rate by 25%, from 1000 Mbit/s to 1250 Mbit/s, to ensure a DC balanced signal. The symbols are then sent using NRZ.

IEEE 802.3ab, which defines the widely used 1000BASE-T interface type, uses a different encoding scheme in order to keep the symbol rate as low as possible, allowing transmission over twisted pair.

VincentP · Feb 25, 2014

Someone Somewhere :

This is how I think it works:
Take 8 bits of data.
Expand this into 4 x 3 bit symbols.
These symbols are sent at 125 million symbols per second on the four available pairs (apparently in both directions at once).
125M * 8 = 1Gbps data rate.

Someone Somewhere · Feb 25, 2014

Nope; you can run at full speed in both directions simultaneously.

Remember that each symbol has 5 possible voltage levels.

Working out exactly how they're transmitting the data is somewhat irrelevant - you can spend hours reading the entire specs if you want, but it starts to get a bit pointless.

VincentP · Feb 25, 2014

Details of encoding aren't important to the user. My point was that the data rate is 1Gbps after encoding, consistent with your original post.
Not sure what you mean by "Nope; you can run at full speed in both directions simultaneously."
My comment was "apparently in both directions at once", which seems like the same thing.
I just find that interesting because 100 base TX uses a single pair in each direction.

Someone Somewhere · Feb 25, 2014

These symbols are sent at 125 million symbols per second on the four available pairs (apparently in both directions at once).
125M * 8 = 1Gbps data rate.

That can't be the case if it's full duplex.

There is a 1000baseTX which uses one pair in each direction, but it didn't catch on. Everything is 1000baseT (unless you start talking fibre, which gets complex).

My guess is that the OP's plugs aren't correctly terminated.

VincentP · Feb 25, 2014

Someone Somewhere :

The 1000 base T standard uses all four pairs in both directions simultaneously.
"In a departure from both 10BASE-T and 100BASE-TX, 1000BASE-T uses all four cable pairs for simultaneous transmission in both directions through the use of adaptive equalization and a 5-level pulse amplitude modulation (PAM-5) technique."
Wikipedia article: http://en.wikipedia.org/wiki/Gigabit_Ethernet
Cisco article: http://www.cisco.com/en/US/tech/tk389/tk214/tech_digest09186a0080091a86.html

This has nothing to do with the original post of course, it's just interesting.

The issue is likely bad termination on the fixed cables (possibly not all four pairs being terminated) or exceeding the cable length that the switch can support, which may not meet the 100m standard.

Someone Somewhere · Feb 25, 2014

I doubt it's the switch - existing cable works fine. Termination is the obvious issue; it's so easy to not have them all the way into the plug, if you're terminating directly into plugs. Patch panels are harder to screw up.

Also, very few houses have cables even approaching 100m.

Why won't my network run at 1 gig?

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