router transmits on two pins 1,2

[sarahr202]

Hi everybody.

We  connect router say to a computer using a cross over cable, router uses pins 1,2 to transmit and pins 3,6 to receive.

My question is why do we need two pins to transmit? Can we not use just one pin to transmit say pin 1?

What is the benefit of using two pins i.e pin 1 and pin 2 to transmit data?

thanks and have a great weekend.

[Reza Sharifi · Accepted solution]

Hi Sarah,

That is based on 568A standard cabling.  You need a pair for example for transmit, one is white/green with BI_DI+ and one is green with BI_DI-

See this link for more detail:

http://www.ertyu.org/steven_nikkel/ethernetcables.html

HTH

[sarahr202]

Hi Reza and Singh

I hope you guys are doing fine.

The links you  did not address the question asto why we need two pins such as pin 1 and pin2 on a router to tranmit data. What are the benifits using two pins insted of one for tranmission.?

Thanks and  have a great weekend

[singhaam007]

hello Sarah,

i am doing good, thanks .

It was cat 3 cable with 2 pairs only because its bandwidth was 16 MHz (16 million bits per second). Unsuitable for speeds above 16 Mbit/s. Now mainly for telephone cable.early 2000s most new structured cable installations are built with Cat 5e (100 million bits per second) which achieves speeds of 100 Mbit/s by using all 4 pairs of wires. So to achieve this higer speed bandwidth we need 2 pair to transmit and 2 to receive. 3^rd pair used for POE and 5^th for gig transfer.

Hope this will help.

thanks

[singhaam007 · Accepted solution]

Hello Sarah,

(abbreviation: Tx and Rx) is the process of sending and propagating an analogue or digital information signal over a physical point-to-point or point-to-multipoint transmission medium,

1- The sending of a signal from the transmitting end of a telecommunication circuit to inform a user at the receiving end that a message is to be sent.

2-A data transmission circuit may transfer information in (a) one direction only, (b) either direction but one way at a time, or (c) both directions simultaneously

These are the wiring standards T568A and T568B

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

hope this will help.

thanks

[Giuseppe Larosa · Accepted solution]

Hello Sarah,

>> What is the benefit of using two pins i.e pin 1 and pin 2 to transmit data?

From an electrical point of view the use of two pins is a form of balanced transmission the information in the signal is coded as the difference in voltage between the two pins

The alternative to this would be an unbalanced setup with a single common ground pin for all transmission pairs.

The benefits of balanced transmission are better resistance to noise and specially less vulnerable to cross talk between different pairs either carrying a signal in opposite direction or in the same direction of the given pair.

Being the actual signal associated to the difference all forms of noise that influence both wires are minimized ( common mode noise rejection)

Reduction of cross talk is the reason behind the twisting of pairs in an UTP cable

Unshielded Twisted Pair

unshielded means that the external cover of the cable is not connected to ground.

see

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

Hope to help

Giuseppe

[sarahr202]

Thanks Giuseppe for the detailed response

The use of balanced line reduces noise while twisting reduces cross talk.

Balanced line consists of two conductors.

In case of gigabit ethernet, we use four pins or two pairs to transmit.

So in case of gigabit ethernet, we use two balanced lines to transmit data. The use of two balanced lines is one of the reasons why we are able to acheive 1000bits/sec . Is it correct?

Have a great weekend.

[Reza Sharifi · Accepted solution]

Hi Sarah,

Usually, you use 2 pairs (4 conductors) for 100Mb Ethernet and 4 pairs (all 8 conductors) for Gigabit Ethernet and 10Gig.

Have a nice weekend

Reza

[Giuseppe Larosa · Accepted solution]

Hello Sarah,

>> The use of two balanced lines is one of the reasons why we are able to acheive 1000bits/sec . Is it correct?

yes, the bit stream is divided in two substreams that are sent in parallel on the different transmission pairs.

To be noted the actual speed on the line is greater then 1Gbps  because the bit stream is encoded with some overhead to provide error detection and correction.

The actual speed on the wire is 1250 Mbps but the code used is 8 bits of data mapped in 10 bits sent on wire.

see

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

Hope to help

Giuseppe

[sarahr202]

Thanks Giuseppe.

[darren-carr]

Hi all,

Further to your discussions above, and just to clear this up....

If I am a PC I am using pins 1 & 2 to transmit to a switch, and am using pins 3 & 6 to receive from a switch.

If we had a bit stream of 000111000011110000111100000111 are the 1's transmitted on pin 1 and the 0's on pin 2?

And for receive pin 3 is used to receive 1's and pin 6 used to receive 0's from a switch?

And for a switch, a switch sends 1's on pin 3 and 0's on pin 6 and receives 1'son pin 1 and 0's on pin 2?

I am just trying to clear this up. I've gone through a few docs but am struggling with this concept somewhat!!! Silly I know as this is the basics, but I want to strip this right back to get a better understanding.

Sorry for hijacking the thread!

Cheers,

D