Actual Max Speed on Cat5E with Gigabit Ethernet

Quote: http://www.swhowto.com/WhatWant.htm     What Do You Want?
These standards are more than a bit confusing and are changing as well. Added to that many cable suppliers are stating that their cable will work at higher bit rates. Those claims are probably correct.  But, here is the commonly accepted simplification of all this:
Cable Rating Bit Rate
CAT5 up to 100Mbps
CAT5e up to 100Mbps
CAT6 up to 1000Mbps
...
Recently the IEEE standard for Gigabit Ethernet was approved and this now calls for Gigabit Ethernet to operate over standard CAT5 cable. This is now called

But aware too that Gigabit Ethernet  or 1000BASE-T actually uses ALL 4 pair of the CATx cables where 100Base-T Fast Ethernet and 10Base-T only used two of the four pairs. See my Links page for more on Gigabit Ethernet.

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http://fourpair.blogspot.com/2005/02/what-is-difference-between-cat-5e-and.html  Network Know How: What is the difference between Cat 5e and Cat 6?
"All cable rated Cat 5e or Cat 6 is capable of Gigabit Ethernet. The MHz rating is just the frequency range used for testing the cable."

This issue is hardly that simple, and depends completely on the used protocols and signaling. For example, 10GbE is operated on CAT5E and CAT6. Do you want to know what speeds the cable standards are currently rated for or some theoretical figure of how fast speeds they could support with current/future technologies?

2 Gigabit switches with ports 1000BASE-T are interconnected with Cat5e Cable.
i want to know what is the actual practial speed that can be achieved over Cat5e cable.
the GE Fiber optic can run at 2Gbps Full Duplex between the switches.
However the Cat5e runs at much lesser speed,
I need to know the figure.

regards
naren

 

>>speed
i mean the actual throughput on Cat5e, which is less than 50feet in length

In the real world, realistically, you can get up to about 40Mbs on Cat 5e connected to a 100Mbs card, and 100Mbs. This is because the ethernet protocol basically states - listen, and if nothing is being transmitted, then transmit. This means that at 40Mbs, there is a 2/5 chance of a collision, which results in the packets concerned becoming damaged, and retransmitted usinf a fancy exponential backoff algorithm:

http://en.wikipedia.org/wiki/Truncated_binary_exponential_backoff

This helps prevent the network from being overloaded, and failing completely as more packets fail, get retransmitted, and hence have a greater chance of failing again:

http://en.wikipedia.org/wiki/Congestion_collapse

There is also the requirement for each packet to be acknowledged, taking the *real* data throughput (without the the protocol overheads rather than the raw packet throughput) down to about 25-30Mbs (acknowledge packets are smaller than the average packet).

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?????????

I always thought the CAT5e will give much less throughtput than the gigabit fiber ,using  tcp/ip protocol
i also suggested the same to others...
i say somewhere on the internet which mentioned the same above thing.

so you say that the fiber and 1000BaseT will give same throughtput???

>so you say that the fiber and 1000BaseT will give same throughtput???

They are both capable of providing the theorectical throuput of 1000Mbps....*BUT* in the real world, both ends of the cable are not clocked, and communication is not 1 way only. As a 'protocol' is required too control the traffic, you have significant losses. In addition, the interfaces at each end, or the network beyond the interfaces will always have limitations.

These protocol limitations are mentioned above, and give you a 'real data' throughput of about 25-30% of the rated capacity over Cat 5e or Cat6. Fibre is a little different as if you are working with a fibre 'loop' rather than a single fibre, it does become possible to get closer to the 50% of rated capacity, provided the buffering at either end is adequate. You can actually get slightly over 50% in artificially 'tuned' data transfer situations.

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I can't give you the exact figures, but I've heard Cat5e is somewhere around 600Mb and Cat6 is around 800Mb max realistic throughput.

These statements are a little misleading:

>>"In the real world, realistically, you can get up to about 40Mbs on Cat 5e connected to a 100Mbs card, and 100Mbs. This is because the ethernet protocol basically states - listen, and if nothing is being transmitted, then transmit. This means that at 40Mbs, there is a 2/5 chance of a collision, which results in the packets concerned becoming damaged, and retransmitted usinf a fancy exponential backoff algorithm:"

This is an OLD Ethernet network.  Modern switched networks operating at Full Duplex actually TURN OFF collision detection circuits - which is the root cause of duplex mismatches.  They therefore don't need to listen, because both transmit and receive can operate at the same time since there are "only 2 nodes" on the segment - the device, and the port.

>>"There is also the requirement for each packet to be acknowledged, taking the *real* data throughput (without the the protocol overheads rather than the raw packet throughput) down to about 25-30Mbs (acknowledge packets are smaller than the average packet)."

This depends - if it's a stateful protocol such as TCP.  However, stateless protocols such as UDP do NOT require each packet be acknowledged.  In addition, with FULL DUPLEX, the ack comes back over a seperate "line" from the transmit, so it's not impacting traffic flow at the physical wire - but instead in the devices hardware - memory and cpu.

>Modern switched networks

Most consumer systems are still broadcast hubs! - I accept that this is the case if you get a Modern Cisco switch. However the points made still apply to the majority of hubs bought for the 'consumer.

Other than that - fair comments, but I was trying to simplify it, and the end result figures are bourne out in the real world. For example, the majority of traffic (in most homes, and companies) is TCP rather than UDP. For network calculations we are even more consevative stating that the average thoughput at peak times must not exceed 15% of the 'theorectical connection' capability allowing a 100% overhead.

There are good reasons for this as the labour costs for cable installation are normally fairly high relative to the cable costs, and adding additional cable for future growth is normally a very good idea.

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I get the point now.......
but could you confirm this again...

1.connecting 2 backbone switches with gigabit fibre optic cable
2.connecting 2 backbone switches with 1000BaseT Cat5e cable
Which one will give better throughput with TCP/IP protocol.

there is a bottleneck problem, i am expecting this Cat5e cable is causing the issue.
if cat5e is causing the bottleneck then i could use gigabit fibre optic instead or
aggregate 2 1000BaseT ports for connecting 2 backbone switches.

I am using Cisco catalyst and HP Procurve switches(latest).

I need the figures and a hyperlink to support my point i.e"gigabit fibre gives more throughput than 1000BaseT cat5e cable"

regards
naren

>there is a bottleneck problem,
Are you using a CAT5 Crossover cable between two switches?
I'll say it again - the fact that you are using CAT5e copper should not be the bottleneck.
If you are using a standard crossover cable, then your termination is the problem. A Gigabit crossover cable pinout is very different from a standard cat5 crossover. Remember that gigabit uses all 4 pairs, not just two. If you use a standard crossover, then only two pairs are working.

i am using a straight through cat5e cable, the switches are in auto sensing mode

i think no one have real proof to claim that gigabit fibre optic cable gives more performance than 1000BaseT Cat5e cable.

all over the internet they mention both are Gig.

but actual throughput in the realworld is still a mistery!!

It's just generally understood, you maximum throughput will be fiber.

I agree with lrmoore - we have fiber backbones running GigE, we HARDLY EVER get off the flatline of minimual utiization on our interswitch links, and we have about 600 users in this building.  How do you know the problem is the GigE link?  Do you have some tools you're testing/monitoring with?  What about port errors?

I took irmoore's comment

and desided that both cat5e and fiber are capable to run at 1000Mbps.



thanks
naren