OT: Network Speed

[Endulini]

Hi Folks,

I have already posted this on uk.comp.home-networking but folks here are generally pretty savvy so thought I'd cross-post here as well......

I've recently had installed some cabling to various rooms in the house and have noticed, via a couple of network switches that indicate the connection speed (i.e. 10/100/1000Mbps) that some of the new connections are not running at 1000Mbps where I would expect. The interfaces are all rated at

1000Mbps and the cabling used was Cat 6. Is this likely to be down to how the RJ45 plugs and faceplates are wired? Is there anything I should consider?

Cheers.

[John Rumm]

Have you actually testes that all 8 point to point connections are good? Gig ethernet needs all the pairs connected.

[NY]

What speeds are the computers at the other end of the cable capable of supporting. If you have a 1000 Mbps (gigabit) router/switch plugged into a PC that has a 10/100 card, the connection, as reported by the router and the computer, will be 100 Mbps.

However if the computer also has a gigabit card, then that's that theory shot down in flames! What happens if you move a computer from the far end of the Cat 6 and plug it into the router via a short length of cable - does the reported speed increase?

[dennis]

Have you tested the links with a cheap tester yet?

GigE uses all four pairs and you may only get 100M or nothing if one pair is broken.

You may not get the speed even if the link connects if you have mixed up pairs.

[Nick]

Also when I did mine, with Cat 5e, kinks in the cable caused it to drop down to 100Mb/s

[Endulini]

Thanks all, one further question how would I test the faceplates?

[Nick]

Have you tested the links with a cheap tester yet?

[John Rumm]

With a network testing tool...

These you can divide into three classes of device:

1) Simple pin continuity testers - they will test that each pin at one end is connected to the right pin at the other. A quick simple go/no go indication. They won't spot errors mixing up the pairs such that the pip to pi wiring is right, but you have split the signals over more than one pair. These can be had for £20 or less quite often.

e.g.

or

2) Intermediate testers - they will do as above, but also be able to check for split pairs, measure cable lengths (and possibly distances to cable breaks), inject test tones for cable tracing, and possibly work with multiple slave devices for quickly testing a number of cables in one go. Might include a TDR. Expect to pay £50 - £250.

3) High end cable tester - does all of above plus proper bandwidth and dynamic response testing, near and far end crosstalk measurement, full cable validation to demonstrate compatibility with standards (so you see not only that it "passes" but also can see the margins by how much etc). Usually include a TDR for accurate cable length measurements and also fault location. May include extensive reporting and logging capabilities. Normally include abilities to to higher level network tests like protocol detection, ping, arp, and various other link and higher layer tests. These are normally £300+ into several thousands.

[Mike Tomlinson]

En el artículo , Endulini escribió:

Yes, if you haven't followed the correct wiring scheme, all bets are off. This is the convention used in wiring faceplate and plug:

pin colour

1 orange/white 2 orange 3 green/white 4 blue 5 blue/white 6 green 7 brown/white 8 brown

note how the green pair is split over 3 and 6

if you haven't followed this then you'll have "split pairs" and the connection will be unreliable or flat out won't work.

As others have said, all pins need to be wired for 1000Mbit.

Did you use a proper Krone punchdown tool? If you used a plastic one or a screwdriver, start over with the correct tool. If screwdriver, throw the faceplates away and buy new ones, they'll be wrecked.

Did you kink the cable at any point during install?

Finally, check your patch cables. Some el-cheapo ones only have 4 wires connected (pins 1&2, 3&6). These will be obvious from looking at the plug ends. Those will only work to a max of 100Mbps

[Brian Gaff]

I don't know if this is right but its something I've always wanted to know. If you take one port upstairs then use a network switch to turn it into more ports, I'd always assumed that the full bandwidth of the one port from the router to the switch is shared with the other switcher ports depending on how many are in use at the time. In a case like this the speed would be lower on those from the switch if several were in use surely? Brian

[Nick]

Yes but you will normally only use sustained full gigabit bandwidth for copying large files ,even a gigabyte file takes 10 seconds. If two people try it at the same time you get half the rate.

Most normal usage is low bandwidth, e.g. media streaming is at most tens of Mb/s so many people can comfortably do it at the same time.

[Bob Eager]

Yes. Although the interconnect to my workshop is two cables, and I've bonded those two ports together at each end.

[Roger Hayter]

Yes and no! The switch is able to connect all the ports at the full

1Gb/s. Each connection can send packets to any of the other ports on the switch. So every connection (provided the other end can do it) will have the full bandwidth.

However, if two or more ports into the switch are only interested in sending packets two and from the single port connected to the router then the amount of information that can be passed by all of them will be limited to the 1Gb/s of the router port, and each will have a lower effective signal bandwidth. However, each of the other ports will still have a full 1Gb/s path but will have to keep waiting to use it until the port to the router is free. This queuing will ideally be done at a protocol level (e.g. TCP) above the ethernet layer, to avoid wasting bandwidth by packets having to be repeated until they get through. This is the simple-minded version that I understand - does it make sense?

[The Natural Philosopher]

Except when you have two clients and two servers when the switch should be capable of routing a->b *and* c->d both at full speed.

[Chris Bartram]

A simple first step would be to connect all the devices , in turn, to the switch with only a patch lead. If that comes up at 1G then it's your cabling for sure.

[dennis]

but don't do that on most cheap switches or you will have a broadcast storm.

[Bob Eager]

Naturally. These are designed for bonding.

[Vir Campestris]

I will be surprised if many domestic switches can manage this.

Andy

[Dave Liquorice]

I'd be surprised if yer bog standard PC can fill a 1Gbps link in a sustained manner.

[Tim Watts]

They've been able to do that, near enough, for a while (decent laptop/PC) - I was getting 800Mb/s quite easily in 2005. Of course, whether the PC can *source* useful data at that rate is another matter (how many disks and how fast)

Now 10gig is much more fun :)