At the following webpage, http://www.scope.com/whitepap/white19.htm
it is briefly discussed the concern over pushing 1000BaseT down Cat5. This concern has raised the possibility of introducing another version of Cat5 cable indicated as Cat5-E. I quote ... "Can Better Cabling Help? Since most of the noise in a category 5 channel is due to the crosstalk and return loss properties of the cable, improving the performance of these parameters improves the SNR margin of gigabit Ethernet. TIA is currently in the process of developing a specification for enhanced cabling - category 5E. Category 5E offers 2 dB of improvement in the return loss and ELFEXT performance and 4 dB of improvement in the NEXT performance (figure 12) over category 5. Category 5E is specified by an addendum to TIA-568-A [5], which is under ballot as of this writing." This was written sometime in 1998 by Scope Communications. The use of PAM-5 for pushing 1000BaseT down a 100BaseT line reminds me of an excellent discussion by John C. Bellamy in his book _Digital Telephony_ (I highly recommend getting it). He compares energy spectral density merits of differing line coding and digital modulation techniques to shrink the width of power envelopes thus being able to increase higher data rates into a narrower bandwidth. Using the proper coding techniques, one could conceivably push a very high data rate that would otherwise require a wide bandwidth down a very limited bandwidth medium that would normally respond terribly to such a data rate. At http://www.bicsi.org/shariff/tsld001.htm an excellent presentation is given complete with eye diagrams when viewing the graphic version for Gigabit Ethernet tutorial. And again, some discursion is mentioned concerning the cable. Mr. Shariff presents the following "Coding Scheme for Gigabit Ethernet PAM-5 (Pulse Amplitude Modulation 5 Levels) 2 Bits per symbol ( => 4 bit combinations or levels) Symbol Rate 125 Mbaud/sec Bit Rate per pair 250 Mbits/sec Bit Rate using 4 pairs 1000 Mbits/sec 5th coding level used for control and management Simultaneous Bi-Directional Transmission " I still concur with Don. But, my gut feeling is that a 1000 Mbits/second data rate is capable of producing a data stream such as 10101010 ... or simply a square wave operating with a fundamental of 500 MHz. Or at least a 500 MHz burst. In any event, things will be interesting ... Regards, Doug --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
