1. Field of the Invention
The present invention relates to a cabling media employing a plurality of twisted wire pairs. More particularly, the present invention relates to a twisting scheme for the twisted wire pairs constituting the cabling media, which allows for a relatively higher bit rate transmission, and reduces the likelihood of transmission errors due to alien and internal crosstalk.
2. Description of the Related Art
Along with the greatly increased use of computers for homes and offices, there has developed a need for a cabling media, which may be used to connect peripheral equipment to computers and to connect plural computers and peripheral equipment into a common network. Today's computers and peripherals operate at ever increasing data transmission rates. Therefore, there is a continuing need to develop cabling media, which can operate substantially error-free at higher bit rates, but also satisfy numerous elevated operational performance criteria, such as a reduction in alien crosstalk when the cable is in a high cable density application.
U.S. Pat. No. 5,952,607, which is incorporated herein by reference, discloses a typical twisting scheme employed in common twisted pair cables. FIG. 1 shows four pairs of wires (a first pair A, a second pair B, a third pair C and a fourth pair D) housed inside of a common jacket, constituting a first common cable E. In FIG. 1, the jacket has been partially removed at the end of the cable and the wire pairs A, B, C, D have been separated, so that the twist scheme can be clearly seen. FIG. 1 also illustrates a second common cable J, which is separate from the first common cable E, but identical in construction to the first common cable E. The second common cable J also includes four pairs of wires (a fifth pair F, a sixth pair G, a seventh pair H and an eight pair I) housed inside of a common jacket.
Each of the wire pairs A, B, C, D has a fixed twist interval a, b, c, d, respectively. Since the first and second common cables E and J are identical in construction, each of the wire pairs F, G, H, I also has the same fixed twist interval a, b, c, d, respectively. Each of the twist intervals a, b, c, d is different from the twist interval of the other wire pairs. As is known in the art, such an arrangement assists in reducing crosstalk between the wire pairs within the first common cable E. Further, as is common in the art, each of the twisted wire pairs has a unique fixed twist interval of slightly more than, or less than, 0.500 inches. The table below summarizes the twist interval ranges for the first through eight pairs A, B, C, D, F, G, H, I:
Min. TwistMax. TwistPair No.Twist LengthLengthLengthA/F0.4400.4300.450B/G0.4100.4000.420C/H0.5960.5800.610D/I0.6700.6500.690
Cabling media with the twisting scheme outlined above, such as the cabling media disclosed in U.S. Pat. No. 5,952,607, have enjoyed success in the industry. However, with the ever-increasing demand for faster data rate transmission speeds, it has become apparent, that the cabling media of the background art suffers drawbacks. Namely, the background art's cabling media exhibits unacceptable levels of Alien near end crosstalk (ANEXT), at higher data transmission rates. FIGS. 2-5, illustrate the ANEXT for the wire pairs A, B, C, D of the cabling media, in accordance with the background art.
To measure the ANEXT of the pairs, an industry standard testing technique making use of a vector network analyzer (VNA) was employed. Briefly, to obtain the data of FIG. 2, the output of the VNA is connected to pair F of a cable J while the input of the VNA is connected to pair A of cable E. The VNA is used to sweep over a band of frequencies from 0.500 MHz to 1000 MHz and the ratio of the signal strength detected on pair A over the signal strength applied to pair F is captured. This is the ANEXT contributed to pair A in cable E from pair F in cable J. Contributions to pair A in cable E from pairs G, H and I in cable J are acquired in the same manner. The power sum of contributions from pairs F, G, H, and I in cable J to pair A in cable E is the ANEXT contributed to pair A in cable E due to all the pairs in cable J and is displayed as trace t1 in FIG. 2 on a logarithmic scale.
To obtain the traces t2 through t4 in the graphs of FIGS. 3-5, the above procedure is repeated for the second, third and fourth twisted wire pairs B, C, D in cable E. The graphs of FIGS. 2-5 illustrate the ANEXT for frequencies between 0.500 MHz and 1000 MHz. A reference line REF, described by the function 44.3−15*log(f/100) dB where f is in the units of MHz, is included in FIGS. 2-5 and serves as a reference, above which potentially acceptable ANEXT performance is achieved. Such tests are commonly used to verify the suitability of cabling media to surpass minimum standards and qualify as a cabling media, such as CAT 5, CAT 5e, and/or CAT 6. As can be seen in FIGS. 2-5, the ANEXT for the cabling media of the background art becomes unacceptable in that it crosses the reference line F at higher frequencies between 10 MHz and 200 MHz.
The reference line REF of FIGS. 2-5 will also serve to demonstrate the improved ANEXT performance of the present invention, as compared to the background art. The reference line REF is logarithmic but appears linear when plotted on a logarithmic scale and is described by the function 44.3−15*log(f/100) dB. The same reference line REF will be set forth in the performance graphs characterizing the present invention, and will provide a standard so that the performance results of the background art can be compared to performance results of the present invention.