Full Duplex vs. Half Duplex 1

[Qamgine]

To make wiring of my local network easier I decided to just use the orange and green pair and remove the blue and brown pair for Cat5 RJ45. Four wires were easier to wire than eight. However, I think I have shot myself in the foot. I just got a cisco pix firewall and have the interfaces to Full Duplex. With my current wiring is that what is making my network "hiccup" and seem to slow down to a halt at times?
For a full duplex, do I need all eight wires?

Thank you in advance.

 

[Bobg1]

The "Proper" way to do the wiring is with all 4 pair.
it makes no difference if its half or full, it will still use the same 2 pair of wires.
Are you sure your settings are the same on both ends?
Are you running 10 or 100?

 

[Qamgine]

I am using 4 10mb Hubs and one hub with auto sensing 10/100. Yes, both ends are the same. The wiring itself is fine. I've used this wiring for over a year. I just upgraded from a DSL router to a T1 router and have a cisco firewall in between my network and the t1 router. I do not believe that there is a problem on the firewall side although it's not improbable. I am just making sure that my wiring would not be the cause of network slowdowns on a 1.4mb t1 router with only about 30 people on it at a time.

 

[Bobg1]

If you are running at 10 you will be better set at half duplex.

 

[jimbopalmer]

Full duplex is faster, but very little 10 meg gear uses it, equipment modern enough to do full duplex is often modern enough to do 100 meg.

As alway never select full duplex for just ONE end of a link, this 'never' works. Either set both ends (usually the switch and the computer) or leave both ends on auto.

I tried to remain child-like, all I acheived was childish.

 

[Qamgine]

Okay - I will see if I can get the firewall to go half duplex. Thanks for the tip.

 

[jimbopalmer]

One other comment, just in case you really mean hubs, hubs are ALWAYS half duplex, only switches do full duplex.

Since a hub repeats each packet to every port, only one port can transmit at a time. Switches only send packets to the intended port, so a port can both send and receive. (many of us say hubs when we mean switches, but there is almost no point in hubs at these switch prices)

I tried to remain child-like, all I acheived was childish.

 

[prof1949]

A hub is never able to handle full duplex, only a switch can do it.

 

[dlongan]

I have been reading all through this forum about everyone recommending using all four pairs of wire based on "Paul Kirsh's white paper on CAT 5 design” Although I haven't found it to read I did some research on my own by looking at actually how the network gear manufactures design their equipment and I have found that they DO NOT USE pins 4,5,7, and 8. This was done by physical examination of the RJ45 connectors on 3COM, Intel, and others. My thought was if they at least grounded these pins then it would make sense and logical to connect the unused pins. But as you can find out for your self’s they do not.

So, long story short it's a waste of time to connect the unused pins if they are not being used by the hardware. It will not provide any additional noise suppression or data integrity by using these pins.

Don Longan
Metro Computer Services

 

[franklin97355]

prof1949:
Not true.

 

[franklin97355]

dlongan: Maybe not now, but in the future who knows. How would you feel if you are asked to hook up a peice of equipment that required cat5 standard cable? (at 100 locations)

 

[daronwilson]

Don...I guess I put a lot more trust in the engineers that designed the UTP media, and having fixed many many installations that were done by 'our computer guy', I must disagree with this:

So, long story short it's a waste of time to connect the unused pins if they are not being used by the hardware. It will not provide any additional noise suppression or data integrity by using these pins.

Your statement is kind of like saying 'hey, parallel printers don't use ALL of those 25 pins, so lets make our cords with 25 conductor and only connect the 18 that we need for our application.' It's just silly. Certainly you have run across 'serial cables' with only 3 wires connected that won't work for your application if you want hardware handshaking for example. Please, wire it the way it is designed.

If you don't use all four pairs:

1. Your installation will NOT meet the applicable standards provided by BICSI, ANSI, IEEE and in some states will not even meet state code requirements.

2. Your installation will not support POE (currently being used in the field) or 1000BaseT (currently being used in the field) for example. Why install a system that is already not going to allow current technologies to run on it?

3. You will NOT be able to adequately provide a standard test result for your installation. All bandwidth certification tests require measurements on all four pairs.

So...if you are installing structured wiring with only two pairs connected, someone will be in shortly behind you to do it right.

Good Luck!


It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[p01nt]

I'm a network engineer for a major credit card company and am also a Microsoft Certified Systems Engineer, Cisco Certified Network Professional, and Cisco Certified Design Professional (just qualifying the source of this post.) =)
Just for the record: Most common implementations of Ethernet use 10Base-T for 10Mbps operation and 100Base-TX for 100Mbps operation. There are half-duplex and full-duplex versions of both of these. All of these combinations use a 4 wire, or 2 pair configuration. The wires used are 1, 2, 3, and 6. Ethernet was first commonly used in 10Base-T mode at half-duplex. In half-duplex operation, one pair of wires is used for transmitting information and also for sending control information. The second pair is used for receiving information and for CMSA/CD (Carrier-sense Multiple Access/Collision Detection) operations. During half-duplex operation, when two hosts are communicating, only one can send at a time. The other host listens and receives the information, waits for the transmission to complete and then can send. Hubs are somewhat "dumb" devices in that they simply repeat information they receive on one port out to all other ports on the hub. All devices use the CMSA/CD protocol to make sure that the wire is clear to send. If two hosts do happen to send at the same time, a collision results. So once again, in a configuration using a hub, only one host may transmit information at any given time. What this amounts to in terms of usable bandwidth is this: suppose you have 8 hosts connected to a 10Base-T hub. 10Mbps is the maximum transmission speed of the hub and all users must SHARE this bandwith, which potentially results in 10/8 Mbps or 1.25Mbps of bandwidth per person. Frankly, with switches being so cheap to purchase these days, I don't imagine anyone using a hub either at work or at home anymore.
Switches are more intelligent devices since they act like multi-port bridges. The switch learns the MAC address of the source and destination hosts and switch messages in unicast format to the specific destination. Because of this, on a 10Base-T switch, everyone truly gets 10Mbps operation.
Now for the difference between half and full-duplex operation. I already stated how half-duplex operation works. Full-duplex operation is where the CMSA/CD protocol is turned off and the two wires dedicated to it are enabled to send and transmit as well. What this results in is both hosts are able to send AND receive at the same time. On a 10Base-T switch, since both hosts can send at the same time, this becomes a theoretical 20Mbps operational speed. All that I've said about 10Mbps operation also holds true for 100Mbps, duplex and all!
None of these implementations use all 8 wires for their operations. While there are configurations such as 100Base-T4 out there that use all 8 wires, they are not in common use. The common Category 5 wiring is UTP (Unshielded Twisted Pair) wire and its integrity is determined by how many twists per foot there are. The specification for 10Base-T operation is based on the amount of time it takes for an electrical signal to traverse the wire. In other words there is a max cable length of 100 meters (300 feet) for 10Base-T (and 100Base-T) to operate correctly, and in order for communications to function correctly, the electrical transmission must occur within a specified amount of time. For 100Base-T operation, the IEEE just divided the max transmission time by 10. It is true that 1000Base-T configurations DO use all 8 wires, and so far as I've seen switches for this operation are just now getting into the price range for home use.
The most significant reason I can see for NOT removing 4 wires from your preconfigured Cat5 or Cat5e cabling is that there are twists in the wire which reduce EMI (ElectroMagnetic Interference) which allows for correct operation; for that reason I wouldn't be yanking the wires out. I suppose cutting them off wouldn't hurt, however as a previous post had indicated, if you ever want to use 1000Base-T, you would have to recut the wire. Hope this helps.

 

[dlongan]

Daron,

I do agree after reading about the 1000 base T spec it doesn't make good business practice not to connect all pairs.

Although not using all four pairs in a 10/100 base T installation will not degrade the performance because the 2 unused pairs will not provide any noise suppression as some posts have stated.

I do have a question, the 1000 base T spec states 568A as the standard, but most cable plants are 568B (I know it's only a matter of color coding of pairs) what standard do you recommend as the default installation for a new LAN?

Don Longan
Metro Computer Services, LLC.

 

[daronwilson]

I don't see how the additional two pairs would provide you any noise supression unless grounded, but, I don't have an EE after my name, so I'm placing my trust in the guys that do. They specified terminating all four pairs. You may find no connection of those four wires on the switches and NIC's you checked, but if you look at recent Cisco hardware you will often find the Power Over Ethernet (POE) providing a working voltage on that pair.

EIA/TIA-568-B.1 section 6.2.1 explains that the work station outlets for commercial building installations should be 568A, optionally you may use 568B if necessary to accomodate certain 8pin cabling systems. This section also explains that Federal Government Publication NCS,FTR 1090-1997 recognizes only 568A.

EIA/TIA-570-A section 7.2.4.1 explains that for residential installations, termination shall be in the 568A configuration.

Now that being said, we generally use 568A unless there is a reason to use B (existing installed base, etc.) because it is 100% compliant for all installations.

Good Luck!

It is only my opinion, based on my experience and education...I am always willing to learn, educate me!
Daron J. Wilson, RCDD
daron.wilson@lhmorris.com

 

[RandyVSP]

Cutting thru the clutter and to the point :

I dont hink your really saving that much time just connecting certain pins....go ahead and do them "right" like they should be, then no matter what is plugged in, it will be wired and ready to go.....

Kinda makes it future proof......

Randy

 

[Hitechbuzz]

As several others have said it takes only a few minutes to wire up standard ie. 568A where wires 1&2,3&6 are used for your data, 4&5 phone 7&8 spare. It will save in the long run to keep standard it gives you more flexibilty and saves a hell of a lot of headaches.Then if you require an extra data circuit you can use a splitter & get 4/5,7/8 for them or if you require extra phone the other way.
Cheers Brian

 

[bierhunter]

I'm just going to reiterate what others have stated to help emphasize the importance of trying to keep some standards in networking. We have to also think about the people who will inherit our networks and have to figure out what we did to them.

My recommendations are to always use all pairs. If you don't need them today, you will in the future. VoIP with inline power, Gigabit, etc. If you don't use all pairs now, you will just end up reconnecting everything later. Do it properly now, and you only have to do it once.

 

[rpearson]

I think that what everyone is saying is....Terminate all conductors.Think "FUTURE",and do it right.Later.