1. In a 10Base-T or 100Base-TX environment, what is the used of the other pairs in UTP beside transmit and receive ?

2. Is it possible to increase the size of the MTU. if so, what would be the result ? will the transmission of data will become faster?

6. When talking about serial cable, you are just referring to the various DTE and DCE cable, right?

7 What is the reason why the first ping are taking longer compared to next ping reply? is it because of the ARP process?

8 if you use a public ip address range on a lan, 150.200.x.x example. will it work? even when connected on public internet? what are the cons and pros with this network?

Hi!
I'll give you what I know off the top of my head.

Half duplex uses one pair, full duplex uses two pairs. A third pair can be used for a midspan PoE injector (to provide power to an IP Phone for example), but there's no data through the remaining pairs. Gigabit uses all four pairs.

- thanks, so the third pair can be used for PoE purposes. given that it only needs two pairs for a communication, can i use an telephone wire which only use 2 pairs and insert it to RJ45 corresponding pinouts? why yes and why not?

A frame with an MTU above 1500 is called a jumbo frame. Yes, there's a speed increase, but the switch has to support it. Most consumer grade switches support up to 1500, datacenter LAN switches usually up to 9000. At MTU 9000 (used mainly for Fibre Channel over Ethernet, not really for traditional IP traffic), there's about a 3% less overhead, so 3% speed increase. Not mindblowing.

this is the first time i head about jumbo frame, will look more deeper into this. datacenter lan switches, meaning its in the distribution or core layer? correct me if im wrong, but can it be used on UTP? as you said this is mostly for fiber channel.

For me, yes.

You are correct. You can even lose the first ping if multiple hops are involved.

thank you. would you mind telling me why would i possible lost the first reply that is passing through many hops?

Assuming you NAT it (behind a router) just like any other RFC 1918 private range network, it would work. Pro's: none. Con's: this is not as agreed upon in the RFC, and you will be unable to reach any webserver on the internet with an IP in the 150.200.0.0/16 (150.200.x.x as you've written it) range, because your computer will think it's in the local network, and not find it.

this is really clear, thank you for this. i knew there will be a consequence on doing a public network on lan. will look unto the web to see which the 150.200.x.x has been assigned. so the possibility is for example yahoo.com is on 150.200.x.x chances are whatever i do, i will not reach it? right?

Hope this gives you some insights already.

Half duplex uses one pair, full duplex uses two pairs. A third pair can be used for a midspan PoE injector (to provide power to an IP Phone for example), but there's no data through the remaining pairs. Gigabit uses all four pairs.
thanks, so the third pair can be used for PoE purposes. given that it only needs two pairs for a communication, can i use an telephone wire which only use 2 pairs and insert it to RJ45 corresponding pinouts? why yes and why not?
Good question. I think it will work. I would never do it in a real network of course.


A frame with an MTU above 1500 is called a jumbo frame. Yes, there's a speed increase, but the switch has to support it. Most consumer grade switches support up to 1500, datacenter LAN switches usually up to 9000. At MTU 9000 (used mainly for Fibre Channel over Ethernet, not really for traditional IP traffic), there's about a 3% less overhead, so 3% speed increase. Not mindblowing.
this is the first time i head about jumbo frame, will look more deeper into this. datacenter lan switches, meaning its in the distribution or core layer? correct me if im wrong, but can it be used on UTP? as you said this is mostly for fiber channel.
I know I'm drawing in other topics but I want to give a clear picture Fibre channel as a protocol can run over ethernet. So jumbo frames can exist on ethernet, yes. I'm talking about datacenter LAN switches because I know these support it. Higher end models, like a Nexus 5000 for example. Usually they are used in the network core and distribution as you say. 'Datacenter' here means this is not something you will encounter in a small company's patch cabinet.


You are correct. You can even lose the first ping if multiple hops are involved.
thank you. would you mind telling me why would i possible lost the first reply that is passing through many hops?
Because the first hop has to ARP, then the second hop, then the third... That may take more than five seconds including round-trip time, after which your computer considers the first ping lost. The second will then traverse all hops fast, as they have the right ARP information already.

Assuming you NAT it (behind a router) just like any other RFC 1918 private range network, it would work. Pro's: none. Con's: this is not as agreed upon in the RFC, and you will be unable to reach any webserver on the internet with an IP in the 150.200.0.0/16 (150.200.x.x as you've written it) range, because your computer will think it's in the local network, and not find it.
this is really clear, thank you for this. i knew there will be a consequence on doing a public network on lan. will look unto the web to see which the 150.200.x.x has been assigned. so the possibility is for example yahoo.com is on 150.200.x.x chances are whatever i do, i will not reach it? right?
Correct, and that is why this 'rule' about private addresses was made. No single public server on the internet uses a private IP for communication.

-Thank you sir, i've mistaken Fibre into Fiber. haha. So Fibre Channel is a protocol that allows jumbo frame to pass trough on ethernet.

Wait, let's get that straight. Fibre Channel is a protocol, correct, that works apart from TCP/IP. I mentioned it because it often uses jumbo frames. But 'standard' TCP/IP can use jumbo frames too!

a PCM (pulse code modulation) convert analog voice into a digital signal