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New Member

UTP Cabling

                   HI,

In UTP cable we will be using only 2 pairs (4 cables ) for straight and cross over cables. Why we wont use remaining four cables.

OR in which case do we use all these 8 cables for RX and TX

Please let me know.

Thanks in advance

Naveen

12 REPLIES
New Member

Re: UTP Cabling

This will depends on other factors; speed, poe
You cant get gigabitethernet with two pairs only

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VIP Super Bronze

UTP Cabling

Hi,

For speed up to 100Mb, you only use 2 pairs. For Gig or 10Gig you need to use all 4 pairs.

Have a look at this link :

http://pinouts.ru/NetworkCables/ethernet_10_100_1000_pinout.shtml

HTH

Silver

UTP Cabling

UTP has 8 wires (or conductors)

There are standards on what each wire will do depending on the pinout in the connector.

http://www.zytrax.com/tech/layer_1/cables/tech_lan.htm

There are also BISCI standards that the industry follows based on IEEE.

Hall of Fame Super Gold

UTP Cabling

In UTP cable we will be using only 2 pairs (4 cables ) for straight and cross over cables.

If you want to terminate only two pairs (out of four) then the most you can get a client on this link is 100 Mbps and no PoE.

Power over Ethernet (PoE) requires a pair and GigabitEthernet requires another pair. 

Bronze

UTP Cabling

PoE compatible with cable sharing, so PoE work for 2-pair 10/100BASE-T...

Sometimes in my practice have to use the cable sharing by Siemon modular Y-adapters which convert one 4-pair jack ethernet into two jacks... PoE work well...

Please look at this article for example:

http://www.siemon.com/us/standards/13-19_ieee_802_3af_power_over_ethernet.asp

New Member

UTP Cabling

aukhadiev

I agree with you, but not all devices will work with PoE over 2 pairs. Please check this link:

https://supportforums.cisco.com/docs/DOC-10259

Bronze

UTP Cabling

Thank you, I will keep it in mind...

p.s. more knowledge is always welcome...

New Member

UTP Cabling

Hi aukhadiev,

Thanks for the reply.

You mean to say for 100Mbps 2 pairs or enough. POE requires one pair and Gigabit ethernet require one pair right?

In case if i want 10G/100G with POE is it possible to get with existing 4 pairs only.

Hall of Fame Super Gold

Re: UTP Cabling

Are you kidding? 100Gbps? Copper???

There is no such thing as 10Gbps or 100Gbps with PoE.

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Bronze

Re: UTP Cabling

Hi, naveen kumar...

...for "100Mbps" (100Base-TX)  two wire-pairs are enough inside a category 5 or above cable...

...PoE required two wire-pairs, “active pairs” (called Alternative A) or the “unused pairs” (called Alternative B)...

...Gigabit ethernet (1000Base-T) use all four wire-pairs inside a category 5 or above cable...

New Member

UTP Cabling

Hi Aukhadiev,

Thanks for the reply,

If we use Gigabit ethernet (1000Base-T) it uses all 4 pairs, so do we get POE with Gig ports or we get only with 100Mbps ports.


Hall of Fame Super Gold

Re: UTP Cabling

If we use Gigabit ethernet (1000Base-T) it uses all 4 pairs,

Fat chance you'll get GigabitEthernet with only 4 pairs.    Don't believe me?  Try it:  Get a GigabitEthernet-capable client, a GigabitEthernet switchport and a patch cable with Pairs A and B only, make sure speed is set to autonegotiate.  When you connect the client to the switch, the link won't come up (at GigabitEthernet speed) until you specifically configure the port to negotiate to 10/100 Mbps.

so do we get POE with Gig ports or we get only with 100Mbps ports.

This is how Cisco implements UTP cabling on their switches:

1.  Pair A - This the Layer 1 pair.  This pair will determine if your link should go up or down;

2.  Pair B - This is the Layer 2 pair.  You need a minimum of Pair A and Pair B just to get something going.

3.  Pair C - PoE pair

4.  Pair D - GigabitEthernet pair

If you only have a cable with Pair A and Pair B then the most you'll get is FastEthernet speed, and nothing else.  You won't get GigabitEthernet and/or PoE.

Naveen,

You seem to be pretty much determined to push 1-, 10-, 100Gbps and/or PoE with only 2 pairs in a cable.  What are you trying to accomplish?  I am very certain there is no place for 2-pair patch cables in modern times.  You can use 2 pairs only in analogue phones.  If I find UTP cables with only 2 pairs in my network, I always cut it in half and throw it in the trash.

I am know to have "rejected" a shipment of patch leads back when the supplier tried to "deliver" an order.  They even told me, "Why do need all four pair?  Two pairs is FAR SUPERIOR than four pairs because it generates LESS HEAT".  I told them to give me hard facts and they never responded.  A few months later, I had the same supplier "black listed".

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