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Vonage Thanks for your inputs. I am very interested in what you told me. However, there
Thanks for your inputs. I am very interested in what you told me. However, there are a couple of things as I will describe below that have convinced me that it is perfectly OK to use the two unused twisted pairs to transmit Ethernet signals.
1) My testing setup included a 100-meter long CAT5 cable with a RJ45 splitter at one end connecting two computers and another RJ45 splitter at the other end connecting two Ethernet switch ports of a Router, both of the two computers "ping" to the router at the same time. The length of "ping" packets was set to the maximum length 1518B. After being left running overnight, the result showed only a couple of packets got lost. I did not remember the total number of packets being transmitted, though.
2) I also did some calculations on the added cross talks (NEXT loss) when the two unused twisted pairs are also used to transmit another channel of Ethernet signals, and the added cross talk is still within the 100Base-TX specification. See the picture below, Figure (A) is what I copied from IEEE802.3 regarding the minimum near end cross talk (NEXT) loss, and Figure (B) is the maximum near-end cross talk (NEXT) that one transmit pair of a Cat5E cable can cause. transmitting on the unused twisted pair is equivalent to increase the cross talk by 3dB (doubled). You can pick up different frequency points to compared the two numbers. For example, at 100MHz, the NEXT loss required by IEEE 802.3 is 27.1dB minimum, the total cross talk caused by two transmitting pairs within a CAT5 cable is 35.3dB-3dB=32.3dB, which is still more than 5dB lower than what IEEE802.3 requires (these dB number are actually negative). Therefore I believe it is safe to use the two unused pairs for a second 100M Ethernet signals.
3) Cisco has a 96-port Ethernet switch that uses two unused twisted pairs for a second Ethernet signals. Here is the link to the Cisco's web page:
Cisco Splitter Patch Panel
Pay attention to what they said below:
" The splitter patch panel is used with the WS-X6148X2-RJ-45 10/100 Ethernet module to provide you with 96 Ethernet ports. The WS-X6148X2-RJ-45 Ethernet module has 48 physical RJ-45 connectors. By utilizing the two unused Ethernet pairs in each connector, the port density of the module is doubled."
Thus, If I don't miss something in a big way, I am really confused by what you claimed that you can only run at 10M when the splitters are used.
Can you describe in a little more details how you do the CAT5 testing with RJ45 splitters installed?
I am wondering if or not the cables you are using are just CAT3, not CAT5. CAT3 is not good to run even one Ethernet sginal.
John
Read The Full Thread: Use RJ45 splitters to connect a PC and an ATA by one Cat5
• [color=Blue:d9f0923bbd] RJ45 CABLE SPLITTER - Use it to connect PC and VoIP ATA
• Wierd. In your examples, why would you not just plug the devices directly into
• These have been around for years.
Work fine with 10M, can cause problems with
• Yeah, 100 and 1000 were what I was thinking about. If anyone is still running 10
• -
This RJ45 splitter definitely works with 100M Ethernet or fast Ethernet.
• By using a pair of RJ45 splitters connected by a CAT5 cable of 4 twisted pairs, which
• Your test is meaningless. It's a single, isolated, uncontrolled configuration.
• zq - who are you, what happened to dualcomm?
what were your stats at the mac
• I was surprised it showed up as "zq". I did use "zq" as an ID somewhere else. I guess
zq posted "Thanks for your inputs. I am very interested in what you told me. However, there" on 05/23/2007 |
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