Tham khảo tài liệu 'krone - white paper - truenet - do standards go far enough - 2003', công nghệ thông tin, quản trị mạng phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | WHITE PAPER 1 of 4 pages Do the Standards go far enough? Current position and focus of Standards versus what we now know regarding component matching. For some time now we have had ratified standards throughout the world relating to generic, or structured cabling. We have seen progress from the initial Category 3 cable and connectors, to Category 4 albeit very briefly, to Category 5 where we are today. We have also seen a shift of emphasis from component specifications to link and channel specifications which is somewhat more meaningful to the end user. In more recent times we have seen many drafts of Category 5 Enhanced, or Cat 5E, and Category 6 and 7. All of these specifications focus heavily on bandwidth, with progression from 16 MHz for Cat 3, to 20 MHz for Cat 4 and 100MHz for Cat 5. Category 5 Enhanced still focuses on 100MHz of bandwidth, with some parameters tightened and some new parameters added. Category 6 doubles this bandwidth to 200 MHz, so it is a quantum leap over Cat 5/ Cat 5E. Category 7, if it ever comes to fruition, takes a further giant leap to 600MHz, however it will be a heavily screened solution with possibly non-RJ45 connecting hardware. As previously mentioned, we have seen many drafts of both Cat 5 Enhanced and Cat 6, but the actual ratified published versions seem to be forever coming but never arriving. In fact, as this paper is being written, we are up to draft 12 of Cat 5E! So why the delay? Well, a couple reasons come to mind. Firstly, and most importantly, there is an ongoing problem with a relatively new parameter called return loss. Return loss is a signal echo resulting from inconsistencies in the channel structure, mainly due to poor component impedance matching. The other reason is that it is no easy feat to produce a Category 6 jack that performs adequately at 200MHz and that remains backwards compatible with Cat 5 patch cords. WHITE PAPER 2 of 4 pages Return Loss (RL) Let me come back to the issue of Return Loss (RL). For .
