Only connecting two computers: Gigabit crossover cable or Gigabit switch?

[CZroe]

I still don't fully understand how a Fast Ethernet switch can be "full duplex" and a CAT5 crossover cable can't, but does Gigabit have the same restriction (Full duplex only with a switch)? Which should I use, crossover or a switch?

My usage will be fairly intensive. Daily DVD and CD image transfers, weekly hard drive imaging, file access and storage for both the laptop and the media machine on the fileserver.

I do plan on adding a Windows XP Media Center HTPC to the mix someday and Gigabit will come in handy for off-loading all that Media Center content and accessing everything the rest of the computers have access to (It will be exclusively connected to the HDTV). I figure that a switch will be used/required in the future, but I really don't have the money now unless performance will suffer. Only the media machine and the fileserver will use Gigabit. The laptop uses 802.11g, so it's irrelevant.

Also, I was told that Gigabit crossover cables are made much differently than 10/100 crossover cables so unless you KNOW that the answer applies to Gigabit Ethernet also, please don't assume it does and missinform me

 

[John]

Originally posted by: CZroe


Also, I was told that Gigabit crossover cables are made much differently than 10/100 crossover cables so unless you KNOW that the answer applies to Gigabit Ethernet also, please don't assume it does and missinform me

The twisted pair of a gigabit crossover is wired slightly different than a conventional 10/100 crossover. As long as you're using cat5 (in most cases)/5e/6&7 (overkill cable and neither standard is approved) that is terminated properly you should not have any problems with them on a gigabit lan. However I am not aware of a crossover standard for gigabit, and TTBOMK most nics will autosense when using a straight-thru cable.

Also, if you have several PC's I'd recommend a gigabit switch to maximize performance and simplify the connections.

** This is now your 3rd "cabling" post in the GHW forum. Please help reduce forum clutter and stop posting new threads! **

 

[CZroe]

Originally posted by: John
Whoever told you the cables are different must be yanking your chain. As long as you're using cat5 (in most cases)/5e/6&7 (overkill cable and neither standard is approved) that is terminated properly you should not have any problems with them on a gigabit lan. However I am not aware of a crossover standard for gigabit, and TTBOMK the nics will autosense the connection.

Also, if you have several PC's I'd recommend a gigabit switch to maximize performance and simplify the connections.

I dunno about the accuracy because it was from here.

Originally posted by: ScottMac
Not all GigE equipment will automatically do the crossover. Cisco, for example, does not.

A GigE crossover is different than a usual 10/100 crossover, in that all four pairs are crossed, not just pair 1&3 (1&2, 3&6).

Gig Crossover: pins 1->3, 2->6, 4->7, 5->8 (per Cisco's web site).

Good Luck

Scott

Also, how does a Gigabit switch maximize performance and simplfy beyond a crossover cable? For performance, is it full duplex versus half duplex? For simplicity, what could be simpler than a cable with no power supply or additional clients?

Originally posted by: John
** This is now your 3rd "gigabit" post in the GHW forum. Please help reduce forum clutter and stop posting new threads! **

Nope: It's only my second in twenty-five days and fourth since registering three years ago. Only one was posted on any given day. I think that average is pretty unobtrusive My habit of reviewing my threads for answers and replying to them when I happen to log in bumps them up to the top... on the same day. Do I become "rude" all of a sudden because I make replies?

Suggesting that I do this in the networking forum (I would if I were dealing with TCP/IP), do this all in one post or take a week between questions only means that you are suggesting that I purpposely restrict and slow down the learning process: I can't to take a month to learn enough to make my decision! Actual time-sensitive purchasing decisions rest on this.

EDIT:

Originally posted by: John
** This is now your 3rd "cabling" post in the GHW forum. Please help reduce forum clutter and stop posting new threads! **

That's more like it Point taken. I still feel that there there is no courtesy rule which states that one must refrain from posting different questions in an attempt to learn and purposely delay one's own work which requires such information so I will leave my original point. Should one take FOUR YEARS to decide?

 

[skipper2]

I would def go with the switch. Reasoning is as follows:

1. The switch handles packet collisions and you will have a more stable system.
2. It allows you more flexibility for future expansion.
3. Gives you a semi decent firewall.

Skipper2

 

[MercenaryForHire]

Originally posted by: skipper2
I would def go with the switch. Reasoning is as follows:

1. The switch handles packet collisions and you will have a more stable system.
2. It allows you more flexibility for future expansion.
3. Gives you a semi decent firewall.

Skipper2

1. What exactly are they going to collide with? It's point-to-point, full duplex.
2. True.
3. How the hell does a switch have anything to do with his firewall configuration?

GigE also renders "crossover" obsolete ... all ports autosense.

- M4H

 

[skipper2]

Mercenary,

I was asuming that he at least had a Cable or DSL internet connection. Of course if it is just 2 computers you dont need a firewall. But if he is using a HS connection then the collision and firewall question is answered if both are using the net. If it is ONLY 2 computers, then you are right and sorry to have given bad advice.

 

[MercenaryForHire]

Originally posted by: skipper2
Mercenary,

I was asuming that he at least had a Cable or DSL internet connection. Of course if it is just 2 computers you dont need a firewall. But if he is using a HS connection then the collision and firewall question is answered if both are using the net. If it is ONLY 2 computers, then you are right and sorry to have given bad advice.

Not trying to beat down on you or anything, dude. :beer: Just saying that a switch isn't required to have a "firewall" even if he is connected to the outside world via highspeed. I assume he's already got a 100M network and is wondering if he should add a gigabit section or just a point-to-point.

- M4H

 

[skipper2]

M4H,

I know dude, there are just assumptions sometimes. If he is a newbie and his is connected to the net via a cable modem and he wants to connect his other computer to this and he is using the internet sharing from Xp or Me then the firewall cababilities could suck if he doesnt have the XP firewall activated. I just try to assume that the person has the least amouth of knowledge that is assertainable from the post be has given. I would rather someone be safe then sorry, especially if I gave the advice. Of course he could be an expert, he could have Zone alarm or a red box. Who knows. I was giving info based on 2 computers connected together, sharing a cable connection from puter 1.

 

[sharkeeper]

GLAN's are handy for sure!

If your adapters and switches handle jumbo frames (16128 bytes) and are not sharing the PCI bus with other hungry peripherals (better yet on their own 133MHz PCI-X! ) you should see nice transfers. Typical is around half a gigabit when sharing files and real close to 1Gb using FTP like the example here. (This is always under the presumption that your source and target media can transfer over 100 MB/S both ways AND you don't have an overloaded, heavily shared bus!)

Cheers!

 

[skipper2]

also sorry for my spelling. guess i had a beer or 2 too many.

 

[CZroe]

Originally posted by: MercenaryForHire

Originally posted by: skipper2
I would def go with the switch. Reasoning is as follows:

1. The switch handles packet collisions and you will have a more stable system.
2. It allows you more flexibility for future expansion.
3. Gives you a semi decent firewall.

Skipper2

1. What exactly are they going to collide with? It's point-to-point, full duplex.
2. True.
3. How the hell does a switch have anything to do with his firewall configuration?

GigE also renders "crossover" obsolete ... all ports autosense.

- M4H

Are you sure about that? See that qoute from ScottMac above...

 

[MercenaryForHire]

Originally posted by: skipper2
M4H,

I know dude, there are just assumptions sometimes. If he is a newbie and his is connected to the net via a cable modem and he wants to connect his other computer to this and he is using the internet sharing from Xp or Me then the firewall cababilities could suck if he doesnt have the XP firewall activated. I just try to assume that the person has the least amouth of knowledge that is assertainable from the post be has given. I would rather someone be safe then sorry, especially if I gave the advice. Of course he could be an expert, he could have Zone alarm or a red box. Who knows. I was giving info based on 2 computers connected together, sharing a cable connection from puter 1.

Well, I assumed that since he was asking about setting up a media/backup server with regular drive images, I figured he was beyond the level of "no0b" I ditched ZA a long time ago in favour of a separate BSD box myself.

Originally posted by: skipper2
also sorry for my spelling. guess i had a beer or 2 too many.

From the sounds of that, you'll do just fine around here! :beer::beer:

- M4H

 

[MercenaryForHire]

Originally posted by: CZroe

Originally posted by: MercenaryForHire

Originally posted by: skipper2
I would def go with the switch. Reasoning is as follows:

1. The switch handles packet collisions and you will have a more stable system.
2. It allows you more flexibility for future expansion.
3. Gives you a semi decent firewall.

Skipper2

1. What exactly are they going to collide with? It's point-to-point, full duplex.
2. True.
3. How the hell does a switch have anything to do with his firewall configuration?

GigE also renders "crossover" obsolete ... all ports autosense.

- M4H

Are you sure about that? See that qoute from ScottMac above...

Positive. Every GigE port, NIC or switch - except for potentially the very early ones - is supposed to have full auto MDI-X sensing to make crossover pointless. As of yet, I haven't seen one without such support. Hell, even the Macs have it.

- M4H

 

[CZroe]

OK, but because I still don't understand full/half duplex, I still don't know:

Will I get full duplex with only a crossover cable or does full duplex only work when more than two PCs are involved anyway (Thereby requiring a switch)?

I found a product specification list riddled with problems which claimed "When you connect the PCI Giga Ethernet Adapter to Gigabit Switch or another Gigabit NIC, the speed will be doubled to 2000Mbps (1000Mbps transmit and 1000Mbps Receive)." but then again they also claimed "If you connect the adapter to 100BaseTX hub, the network speed is 1000Mbps"

 

[John]

Originally posted by: CZroeThat's more like it

Correct. I had the common courtesy to edit my initial post and clarify my response. I had initially read your reply the wrong way. Since you seem to reference ScottMac (who is a sharp guy), how about holding a conversation with him instead of relying on others, who you seem to doubt, to answer your questions?

 

[ScottMac]

Not all GigE is autosensing. Some Cisco does not. It is not part of the spec. It depends on the transceiver chipset used in the device. My Cisco 2950 will not autosense and do crossover. My 3550 with copper GBICs also does not. The Gig connection to my game network's cheap-o single-GigE-to-10/100 switch (straight-through), the cheap-o switch autosenses and "crosses-over."

Many / most / all of the "consumer grade" switches will auto-sense, but it's not a given.

RE: Full / Half duplex:

In the good ol' / bad ol' days, hubs were built to emulate a chunk of coax. On coax, only one machine / device / PC could talk at once (if a collision occurred, the colliding systems waited and tried again after going through another listening period. Since the devices could only either talk or listen at any given time, the "conversations" were said to be half-duplex ... only one speaker at a time.

Switches, properly implemented, upped the ante some by providing an apparent bandwidth increase (allowing multiple pairs to be in-session concurrently), and brought about the function of "full duplex." The switching logic allows for traffic to be independently switched on the transmit and receive side; a single station, properly configured with drivers that support it, can be transmitting and receiving at the same time ... possibly to / from two different destinations / sources.

A common analogy is the old two-way radio days, when the end of a transmission was signaled by the word "over;" meaning " I'm done talking, so I'm switching to received mode, go ahead and respond." That would be half duplex: if both sides were in transmit mode, neither side would hear what the other side was saying. First one talks, then the other, according to a previously defined set of rules (a protocol) .... " I will say 'over,' then you go ahead and talk."

Contrast that to today's telephones (even cellular), both sides can blab away at the same time, and both sides can hear what the other side is saying. That corresponds to full duplex. Since the UTP (unshielded twisted pair, Cat 5, 5e, 6 - there isn't a "7") system uses two pair - one for transmit, one for receive - the system (if properly configured and terminated) will support concurrent bidirectional communication (full duplex).

The statement about why you can do full duplex through a switch and not on a crossover cable, if true, would probably be related to the negotiation process to determine how fast each side can talk. Most NICs probably can't negotiate as if they were a switch ... only as a NIC. If THAT's true, then you should be able to get around it by manually setting the speed to 100/full on both NICs and bypass the negotiation process.

The crossover pinout posted was directly from Cisco's website. It is a valid config, and has valid uses. I'd rather have one and not need it than need one and not have it.

JM.02

Scott

 

[onelin]

I have one question.

Why do you CARE about full duplex gigabit? There is no way on earth in two desktop systems you will be getting 120MB/sec *both ways simultaneously* and not likely even 60MB/sec both ways (half duplex) over gigabit. I don't know if using a crossover cable is half duplex vs a switch with full duplex or not, but why does it matter in this situation?

edit: fixed my numbers, on crack this morning

 

[gunrunnerjohn]

If anyone had bothered to read the other exchanges on gigabit connections, you'd see that using typical desktop computers with 32 bit PCI gigabit cards, you'll be lucky to see any significant increase in file transfer speeds, especially writing from the client to the "server". In my tests, I've seen about a 20% improvement when writing large files with 100mbit and gigabit between two machines. Configuring for jumbo frames didn't seem to do anything for the speed, and I'm pretty convinced it's really SMB overhead. Writing from a 2K workstation to a WIndows 2003 Server upped the ante to about 25mb/sec for the writes, which almost makes it worthwhile to upgrade to gigabit. IMO, save your money for a nice USB 2.0 local disk for the speedy backups, it's a better investment.

 

[spidey07]

scott has it nailed.

two computers? Just use a regular cat5e/cat6 cable.

Oh, and half-duplex anything died about 5 years ago. Its a nasty ancient relic of the horror days of networks.

 

[AFB]

You mean 25MBs ?

 

[CZroe]

Originally posted by: John

Originally posted by: CZroeThat's more like it

Correct. I had the common courtesy to edit my initial post and clarify my response.

As did I.

I had initially read your reply the wrong way. Since you seem to reference ScottMac (who is a sharp guy), how about holding a conversation with him instead of relying on others, who you seem to doubt, to answer your questions?

Well, it's a different question and it should be dedicated to the public archive.

All I did with my original reply was answer the "whoever told you" part. After your edit, my earlier response made no sense because it did not quote the original (until after an edit of my own). The only other thing I could have done was to have removed the information from my reply altogether. The information was a key point so instead I simply added a quote of what I was responding to. My response WAS made before the edit, so this is appropriate.

About the second quote::
By the time I had finished tallying up my Gigabit records, and finished that part of my orignal response (In an edit), you had already made your edit (No longer referencing Gigabit). But my origninal point was that there is no courtesy code stating that I must delay a purchasing decision and wait (a month?) between unrelated questions or questions only related because they refer to "gigabit/cabling." Because I HAD made more than one cable-related post on a given day, I acknowledged your new point with the quote. You didn't want acknowledgement? I did not refute it. I will now remove the rest of that quote so it will be clear that I am NOT pointing out your other edit. (Original context here)

Originally posted by: ScottMac
Reply

Thnx! How exactly could I test for full-duplex operation and where would I find that setting for overriding it? I imagine it's not a simple Windows thing

Originally posted by: onelin0
I have one question.

Why do you CARE about full duplex gigabit? There is no way on earth in two desktop systems you will be getting 120MB/sec *both ways simultaneously* and not likely even 60MB/sec both ways (half duplex) over gigabit. I don't know if using a crossover cable is half duplex vs a switch with full duplex or not, but why does it matter in this situation?

edit: fixed my numbers, on crack this morning

Because I can not get anywhere near 120MBps PERIOD (That's a theoretical maximum) so any increase in bandwidth helps. Contrary to the math, Gigabit usually ends up being the bottleneck at around 25MBps. With my usage, things will be going both ways continuously often, including transfers of DVD and HDD images to and from the RAID5 array. Even a miniscule percentage increase in performance would be noticable after a several hour file copy

Originally posted by: gunrunnerjohn
If anyone had bothered to read the other exchanges on gigabit connections, you'd see that using typical desktop computers with 32 bit PCI gigabit cards, you'll be lucky to see any significant increase in file transfer speeds, especially writing from the client to the "server". In my tests, I've seen about a 20% improvement when writing large files with 100mbit and gigabit between two machines. Configuring for jumbo frames didn't seem to do anything for the speed, and I'm pretty convinced it's really SMB overhead. Writing from a 2K workstation to a WIndows 2003 Server upped the ante to about 25mb/sec for the writes, which almost makes it worthwhile to upgrade to gigabit. IMO, save your money for a nice USB 2.0 local disk for the speedy backups, it's a better investment.

Yes, I had fully familiarized myself with your postings in this thread before asking this question. I WILL be writing to a 2003 Server machine, though I have another issue which may prevent me from reaching 25MBps. I'll be making a post about that. Nearly ANY improvement for an $80 investment would be worth it... 20% of 120minutes = 25 minutes of my life and network resources SAVED so I'd put up with even as little as 10%.

 

[cmetz]

CZroe, every 1000BaseT NIC for a PC that I have seen is auto-crossover. Plug them together with a straight cable and it'll figure it out. Yes, it will be full duplex.

 

[VictorLazlo]

I tried to use a simple cat5e crossover cable to connect two gigabit cards, and one of the computers would always lock-up when I tried that. One card was a Broadcom, and the other was a Marvell. The machine with the Marvell card would lockup within 30 sec of establishing the connection. Now I have both computer connected through a 10/100 switch and it works fine.

 

[spidey07]

Originally posted by: VictorLazlo
I tried to use a simple cat5e crossover cable to connect two gigabit cards, and one of the computers would always lock-up when I tried that. One card was a Broadcom, and the other was a Marvell. The machine with the Marvell card would lockup within 30 sec of establishing the connection. Now I have both computer connected through a 10/100 switch and it works fine.

you need a straight thru cable for gig-2-gig connections.

 

[VictorLazlo]

Originally posted by: spidey07

Originally posted by: VictorLazlo
I tried to use a simple cat5e crossover cable to connect two gigabit cards, and one of the computers would always lock-up when I tried that. One card was a Broadcom, and the other was a Marvell. The machine with the Marvell card would lockup within 30 sec of establishing the connection. Now I have both computer connected through a 10/100 switch and it works fine.

you need a straight thru cable for gig-2-gig connections.

I don't know if you are right, but I never even thought to try that.

Worth a shot I guess.