Issues with Cable
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Video Transcription
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>> The next issue we're going to need
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to troubleshoot is our cable.
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Some of the hardware tools that we talked
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about earlier will help with this.
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But I want to spend the next section
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going over some of the common problems with cable.
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To start out, one of
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the most common problems is attenuation.
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Attenuation is all about the fact that
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the signal deteriorates over distance.
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Some cable types are much more
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resistant to attenuation than others.
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For instance, the fiber optic,
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you can go a couple of thousand meters before
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you have problems with signals quality.
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Take that and compare it to a twisted pair.
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You can only get a 100 meters before attenuation.
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That's a pretty noticeable difference.
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Some mitigating strategies with attenuation.
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Many of our devices also amplify signals.
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When talking about switches,
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they're going to boost the signal and
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perhaps other network connectivity devices,
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we'll do the same.
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Keep your run short. Know your type of cable.
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Just a quick review from what we talked about earlier.
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For attenuation, you can usually
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think of 100 meters for twisted pair.
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Regardless of the category.
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You can think of a couple of thousand meters
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for multi-mode fiber and for
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coaxial cable with a thick net which is RD8,
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you can think about 500 meters, know those distances.
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That's going to help you troubleshoot
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any issues with distance.
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Other problems we might have.
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Think of VoIP specifically when I see jitter.
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We also have to think about latency.
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Latency is the delay,
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and certainly not just VoIP
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communications that are subjected to latency.
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If you watch TV, for instance,
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there's an anchor person who was talking to
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one of their correspondence out in the field.
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The anchor person will ask a question.
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Then there's that weird, awkward
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silence where you to tell
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the reporter on the other end
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is just waiting and waiting.
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Then all of a sudden they start talking.
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But then it's apparent that as
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soon as they start talking,
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the message just comes through.
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As awkward as that little period is,
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what we see is over time they can
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>> make their adjustments,
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>> then it's much better.
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With latency you can usually adjust
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and work out that problem.
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Because of the fact that jitter is variable delay
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often caused by environmental situations
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or circumstances,
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it's much more difficult to predict.
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Crosstalk. Crosstalk is a problem
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with copper wires that are
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running adjacent to each other.
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Basically you got signals on one cable that caused
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electromagnetic interference and an adjacent cable.
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That is why the wires are crossed.
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With twisted pair,
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a pair of wires twisted around each other,
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that tends to reduce issues with cross-talk.
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Now, electromagnetic interference,
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this can really interfere with
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traffic pings and on the network.
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You can have a lot of data corruption,
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and this is caused by heavy machinery.
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Bluetooth devices, cell phones devices,
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there are a lot of devices.
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All electronic devices emit some form of radiation.
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How much is going to dictate the degree of interference?
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Twisted pair is particularly susceptible to EMI.
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Because of that, there is an unshielded twisted pair,
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which is the one that's really most susceptible.
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But then there's a shielded twisted pair that provides
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a little bit more shielding
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and a little bit better resistance.
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However, you're still not going to run
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twisted pair cabling down an elevator shaft,
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its just not what it was designed to do.
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We want to keep that in mind that even with shielding,
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there is still a degree of susceptibility.
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Others issues, pin out issues.
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Regardless of if you're crimping your cables.
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Remember, we saw those correct configurations back with
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T568 A and B the twisted pair and RJ-45 jacks.
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Whatever the cable type you're working with,
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you want to test your cable and make
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sure you both send and receive and that
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your pin outs are as they should
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be. Incorrect cable type.
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There are a couple of issues with cable.
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Throughout the years we've certainly evolved to speed.
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We've gone from category three cables to category
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five to category 5e and six.
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Then CAT7 is here.
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Even if it hasn't been officially
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standardized yet, CAT7 is here.
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We've gone from 10 megabits per
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second to 10 gigabits per second.
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What we want to realize is often we may have
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legacy equipment on our network
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or we may be using older cable.
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If you are running CAT3 cable,
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even if our switch transmits a gigabit speed,
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the network is going to be
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forced to run at its lowest component.
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It may be that we're just having
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latency and we're having issues with performance.
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It could be that we're using older cable or
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an older device that operates at a lower speed.
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We also have to think about using AMI,
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using the right cable for this particular situation.
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We've already talked about how twisted pair
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is very susceptible to EMI.
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Well, you can also have that same problems with
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coaxial cable because coaxial cable is very rigid.
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It's not very flexible.
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It's not something that you want to run
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from drop ceilings.
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We definitely want to make sure that we're using
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the best type of cable for our environment.
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Sometimes ports go bad.
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It could be because of EMI.
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A lot of electronic devices
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are particularly susceptible to
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static electricity and ESD, electrostatic discharge.
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It could be an issue,
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it could be any one of a million issues.
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Check your lights.
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Usually we're looking for a green light.
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If that light is yellow for a prolonged period of time,
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or orange, that gives you
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an indication something's going on.
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A lot of times if you see orange or yellow,
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that indicates that there are a lot of collisions,
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certain interference may be working,
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but something's going on in that segment.
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Of course, if you didn't know lights when you plug in,
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that indicates the port may be bad.
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Plugin to another port or
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try different cable on that port.
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Just play around with it.
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Never underestimate the possibility of cable being bad,
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a connector coming disconnected,
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or a port on the switch,
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or whatever device going bad.
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Transceiver mismatch.
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All devices uses transceivers.
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There are transceivers for radio communication,
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for VoIP or a telephony.
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There are transceivers for Ethernet networks.
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Making sure that we have the right transceiver type
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for the right environment, that's a must.
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This just goes back to cables
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being poorly wired or miswired.
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You've got the instances here,
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we've got the reverse or how
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the cables should be configured.
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Good cable testers will tell you which end
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of the cable is configured incorrectly.
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If we talk about duplex,
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we have simplex, half duplex, and full duplex.
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Simplex is one-way communication.
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Can only send in this direction,
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period descending across the wire.
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There is half duplex,
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or I can send and receive,
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but not at the same time.
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Think of a walkie-talkie where we can both communicate,
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but I have to push the button and
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talk and while I'm talking,
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you cant talk. That's half duplex.
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Then there's full duplex,
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which means we can both send and receive simultaneously.
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Most devices today, when we talk about
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switches today, they're full duplex.
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In earlier points in time our switches were half duplex.
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Then as we are moving on to full duplex devices,
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we had ports that would allow auto negotiation.
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Auto negotiation make sure that
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both devices are using the same duplex.
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If you have one device using a different duplex type,
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then the communication will fail.
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It won't work. If you manually
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configure duplex communications and honestly,
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the only driving factor for you to do
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that would be legacy equipment.
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If you do manually configured for half duplex on one end,
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you have to manually configure the other end as well.
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If you leave it on auto negotiation,
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assuming both devices support auto negotiation.
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