Abstract:
A cable has at least a first layer of twisted pairs, having a combination of unshielded twisted pairs, and shielded twisted pairs as well as a second layer of twisted pairs, also having a combination of unshielded twisted pairs, and shielded twisted pairs.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    This application relates to cable construction. More particularly, the present invention relates to an improved LAN (Local Area Network) cables construction. 
         [0003]    2. Related Art 
         [0004]    In the field of cable construction, particularly LAN cables, ever advancing bandwidth requirements are requiring new and innovative ways to meet the desired testing requirements. For example, the cabling standard TIA 568-B.2-10 2008 defines augmented category 6 cabling (Cat 6a). This standard defines the parameters for running 10 Gigabit signaling over Cat 6a copper cable (for 10 GBASE-T). This standard specifies cabling performance to 500 MHz and includes certain performance specifications and test requirements for internal and Alien Crosstalk, among other electrical parameters. 
         [0005]    Typically, in prior art arrangements shorter lay length pairs are used in multi-pair cables to reduce cross-talk. However, shorter lay lengths use more wire per length of cable, and thus there are limitations on how short the lay length can be in any given copper wire twisted pair. Therefore, it is ideal to have the longest lay length possible that meets the desired crosstalk threshold. 
         [0006]    In addition to the crosstalk that occurs between pairs within the same sub-group (unit of 4 adjacent pairs), an additional type of interference occurs between twisted pairs of adjacent sub-groups (4 pairs groups) and between pairs of adjacent cables referred to as ALIEN crosstalk. Although crosstalk within a sub-group (4 adjacent pairs) is easier to manage because the lay lengths of the closest pairs can be tightly managed, ALIEN crosstalk is harder to mitigate within the cable itself due to the sub-group (unit of 4 adjacent pairs) proximity. 
         [0007]    The ALIEN crosstalk is difficult to predict and mitigate since external cable conditions, such as the number of adjacent cables having the same twist rate from cable to cable; the distance between adjacent cables; longer pair lay length in adjacent cables; unknown lay lengths of twisted pairs in adjacent cables; etc. . . . , can not be easily predicted. 
         [0008]    Regarding the application of Cat 6a standards, in particular, in the area of larger 24 twisted pair cables, several different options have been pursued in the prior art. For example, for UTP (Unshielded Twisted Pairs) cables, the 24-unshielded twisted pairs are bundled within the outer jacket into six 4 pair sub-cables, which together are Cat 6a, 10 GBASE-T compliant. Such an arrangement is shown in prior art  FIG. 1 .  FIG. 2  also shows a prior art arrangement with six four-pair sub cable having a central filler. 
         [0009]    In another prior art arrangement in STP (Shielded Twisted Pairs) cables, to produce a 24 pair Cat 6a 10 GBASE-T compliant cable, the twisted pairs are disposed in two concentric layers, the inner having 9 pairs and the outer layer having 15 pairs. Each of these pairs is individually shielded. An example of this design is shown in prior art  FIG. 3 . 
         [0010]    However, in each prior art case, the construction arrangement used to make these cables Cat 6a 10 GBASE-T compliant have added significant size (diameter), weight and costs to the cables. 
         [0011]    For example, the cable shown in  FIG. 1  utilizes a significant amount of additional polymers, such as FRPVC (Flame Retardant Polyvinyl Chloride) for each of the sub-jackets as well as with the larger outer jacket. Not only does this provide an enormous amount of fuel making it difficult to pass fire safety standards, it also adds significant size to the cable making it unsuitable for particular uses. Typically, such prior art cables are approximately 1.0″ in diameter. 
         [0012]    One such standard that these types of cables need to meet is the NEC (National Electric Code) fire safety standard for “Riser” rating, abbreviated—CMR. Cables designed as shown in  FIG. 1  do not always meet the CMR standards and are poorly suited for risers anyway given their large diameters. 
         [0013]    Likewise, the cable shown in  FIG. 2 , also uses FRPVC and has a typical diameter of approximately 0.8″-0.9.″ Such designs utilize a significant amount of shielding, and also have added fuel (because of the thicker jackets on the pair wires themselves owed to the shielding). Furthermore, 24 separate shielded pairs requires 24 separate ground terminations for the installer, which is undesirable. 
         [0014]    In each these two cases, although the cables meet the desired transmission performance ratings, the diameters, weight, cost and other poor design qualities of these cables make them unacceptable for many applications. 
         [0015]    In view of these concerns outlined above, prior art cables have implemented many features necessary to meet various transmission performance standards, but in doing so have negatively impacted the traditional physical standards that cables must also meet. 
       OBJECTS AND SUMMARY 
       [0016]    The present invention overcomes the drawbacks associated with the prior art and provides a 24 twisted pair cable design that reduces ALIEN crosstalk between pairs of adjacent sub-groups (sub-unit of four pairs within a cable as well as ALIEN crosstalk between pairs in adjacently arranged cables. In one arrangement such a cable is cat 6a 10 GBASE-T compliant, while simultaneously being lighter, smaller, easier to produce, more flexible, and less expensive than prior designs. Moreover, a LAN cable according to the present invention may be CMR (riser), CMP (Plenum) CM (general-communication) and LSZH (Low-Smoke Zero Halogen) fire rated and concurrently well dimensioned for such riser usage. 
         [0017]    To this end, the present invention provides for a cable that reduces ALIEN crosstalk between pairs of adjacent sub-groups while reducing the amount of electrical barriers (shielding) or physical spacing required to achieve desired crosstalk performance. 
         [0018]    In one embodiment, a cable is provided at least a first layer of twisted pairs, having a combination of unshielded twisted pairs, and shielded twisted pairs and a at least a second layer of twisted pairs, having a combination of unshielded twisted pairs, and shielded twisted pairs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The present invention can be best understood through the following description and accompanying drawings, wherein: 
           [0020]      FIG. 1  is a prior art cat 6a 10 GBASE-T compliant cable; 
           [0021]      FIG. 2  is a different prior art cat 6a 10 GBASE-T compliant cable; 
           [0022]      FIG. 3  is a different prior art cat6a 10 GBASE-T complaint cable; 
           [0023]      FIG. 4  is a cat 6a 10 GBASE-T compliant cable according to the present invention; 
           [0024]      FIG. 5  is a cat 6a 10 GBASE-T compliant cable according to another embodiment; and 
           [0025]      FIG. 6  illustrates seven adjacently lying cables from  FIG. 4 , in accordance with one embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    In one embodiment of the present invention, as shown in  FIG. 4 , a cable  10  is provided. Describing the elements from the center outwards, a central filler tube  12 , preferably constructed of as a tubular FRPVC element that is used to maintain proper circular cable geometry. It is noted that, in the present application FRPVC is used as an exemplary polymer. However, it is understood that this is intended only as an example and that other polymers may be used as desired, based on particular design implementations of the various embodiments. 
         [0027]    Surrounding central filler tube  12  is an aluminum/polyester shielding tape  14 , metal facing outwards. Layer  14  advantageously provides shielding between the inner layer pairs (described below) for improving cross talk performance. In one exemplary arrangement, tape  14  is a composite tape of 1 mil thickness polyester film with 1.5 mils of aluminum foil, applied longitudinally during the cabling process. 
         [0028]    Around the aluminum/polyester shielded central tube  12 , eight of the twenty four twisted pairs of cable  10  are arranged in a first twisted pair layer  16 . These eight twisted pairs are labeled as elements  18   a - 18   h.  Instead of shielding each of pairs  18   a - 18   h,  as for example in prior art  FIG. 2 , only two pairs, such as pair  18   a  and  18   h  are shielded. Preferably twisted pairs  18   a  and  18   h  are shielded using aluminum/polyester shielding layers  20   a  and  20   h  respectively. Also included in first pair layer  16  are two monofilaments  22 , preferably made of FRPVC, although the invention is not limited in that respect. These monofilaments  22  are added to maintain the proper cable geometry and roundness in cable  10 . 
         [0029]    As shown in  FIG. 4 , preferably, each of monofilaments  22  are disposed opposite one another, dividing first twisted pair layer  16  into two sets of four pairs ( 18   a - 18   d  and  18   e - 18   h ), each of which has one of the two shielded pairs of layer  16 . This arrangement helps balance the structure of layer  16  as well as to spread the cross-talk resisting benefits of the shielded pairs  18   a  and  18   f  around the circumference of cable  10 . 
         [0030]    Around first pair layer  16  is an aluminum/polyester/aluminum wrapping  24 . Over this wrapping is the second pair layer  26  including the remaining sixteen twisted pairs  18  of the twenty-four pair cable  10 . As shown in  FIG. 3 , these sixteen pairs are labeled  18   i - 18   x.  Preferably pairs  18   i,    18   m,    18   q  and  18   u  are shielded using aluminum/polyester shielding layers  20   i,    20   m,    20   q  and  20   u  respectively. The spacing of one shielded pair  18  for each successive four pairs  18  within layer  26  (successive being defined circumferentially) helps spread the cross-talk resisting benefits of the shielded pairs  18   i ,  18   m ,  18   q  and  18   u  around the circumference of cable  10 . 
         [0031]    To obtain the required crosstalk performance between the 4-pair groups in cable  10 , shielding of only a portion of the pairs was chosen. Although spacing can be used (as in prior art  FIG. 1 ) by using increased jacket thicknesses, this results in an overall larger cable design as discussed above. Moreover, as shown in prior art  FIG. 2  each of the pairs are shielded to meet Cat 6a standards. However, to meet the 100 Ohm required impedance, these shielded pairs generally need to be larger than unshielded pairs, resulting in a larger outside cable diameter. 
         [0032]    The present arrangement uses a reduced number of shielded pairs, (six of the twenty four), placing them in strategic locations within the two layers  16  and  26  of cable  10  to have the greatest impact to the crosstalk performance. The other shielding  14  and  24  within cable  10  contacts the shields ( 20 ) on each of the pairs ( 18 ) creating envelopes of individually unshielded pairs resulting in an overall cable  10  which is smaller, weighs and cost less, and is easier to process and terminate. 
         [0033]    Finally, over the outside of second twisted pair layer  26  a polymer jacket  28 , preferably FRPVC, is applied, possibly by extrusion, to form the outer barrier for cable  10 . 
         [0034]    Thus cable  10 , according to the above described design, provides a twenty four pair cat 6a 10 GBASE-T compliant LAN cable. This cable advantageously has a diameter that does not exceed 0.60″, preferably 0.550″, and is also CMR compliant. However, unlike the prior art, the design minimizes the use of shielding material (as opposed to prior art  FIG. 2 ) and does not require complicated and expensive internal sub-cabling (as opposed to prior art  FIG. 1 ). For example, the present arrangement represents a potential reduction in the outside cable diameter of approximately 45% with respect to prior art  FIG. 1  and a potential 67% reduction in shield lengths over the prior art  FIG. 3 . 
         [0035]    In another arrangement, as shown in  FIG. 5 , an alternative arrangement is shown which is substantially similar to the arrangement described above with relation to  FIG. 4 . However, in this arrangement, a third shielding layer  24 (A), preferably made from aluminum/polyester tape, is added around the outside of second twisted pair layer  26 , under jacket  28 . Such a configuration may add additional protection to reduce ALIEN crosstalk with respect to pairs located in adjacently lying cables. 
         [0036]    As an exemplary arrangement,  FIG. 6  shows a typical installation of seven adjacently lying cables  10 . For meeting ALIEN Crosstalk requirements, not only must the individual groups of 4-pairs within cables  10  meet the relevant ALIEN crosstalk requirements, but the pairs must also be able to meet the ALIEN crosstalk requirements with respect to pairs located in the adjacent cables  10 . The embodiments set forth above meet the necessary requirements with significantly less bulk and with greater flexibility than prior art cables, such as those shown in  FIGS. 1-3 . 
         [0037]    It is noted that typical prior art constructions such as those shown in  FIG. 1 , typical 4-pair cable coloring is used within each of the six sub-cables. To visually identify the difference between the 4-pair bundled sub-cables, different jacket colors for these sub-cables is typically used. However, when the outer cable jacket is cut back for termination, the installer still ends up with several individual pairs, from the 24 pair bundle of the same color. In one embodiment of the present invention, it is contemplated that the above described design eliminates the need for multiple jacket colors by following the industry standard color code for multi-pair cables colored directly onto the 24 pairs. 
         [0038]    While only certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes or equivalents will now occur to those skilled in the art. It is therefore, to be understood that this application is intended to cover all such modifications and changes that fall within the true spirit of the invention.