Talk:G.992.1: Difference between revisions
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No it is as User:69.111.160.185 writes above (maybe 222, if we start at carrier 33 and remove the pilot). If nothing else, should your 12 Mb/s for ADSL2 (which uses the same frequencies) indicate that your 8 Mb/s is incorrect. The data frame rate of 4kHz comes from the fact that one includes the overhead of the cyclic extension and the synchronization frame. Also note that carrier 0-6 is typically not used, even for upstream. The difference from 13.3 Mb/s down to 8 Mb/s can either be seen to come from framing overhead, FEC, and control channel overhead. Or, if you look up some early books on ADSL (or the ANSI standard), from the structure of bearer channels. In ANSI T1.413 issue 1 the maximum downstream bit-rate was when all four bearer channels where used and each bearer channel could bear 1.536 Mb/s, that is,the maximum was 6.144 Mb/s! Later on, some clever way of circumvent this was implemented, and the limit ended up being 8Mb/s instead. For ADSL2 these restrictions and the overhead for framing has been reduced and ADSL2 comes (theoretically) much closer to the 13.3 Mb/s than ADSL1. |
No it is as User:69.111.160.185 writes above (maybe 222, if we start at carrier 33 and remove the pilot). If nothing else, should your 12 Mb/s for ADSL2 (which uses the same frequencies) indicate that your 8 Mb/s is incorrect. The data frame rate of 4kHz comes from the fact that one includes the overhead of the cyclic extension and the synchronization frame. Also note that carrier 0-6 is typically not used, even for upstream. The difference from 13.3 Mb/s down to 8 Mb/s can either be seen to come from framing overhead, FEC, and control channel overhead. Or, if you look up some early books on ADSL (or the ANSI standard), from the structure of bearer channels. In ANSI T1.413 issue 1 the maximum downstream bit-rate was when all four bearer channels where used and each bearer channel could bear 1.536 Mb/s, that is,the maximum was 6.144 Mb/s! Later on, some clever way of circumvent this was implemented, and the limit ended up being 8Mb/s instead. For ADSL2 these restrictions and the overhead for framing has been reduced and ADSL2 comes (theoretically) much closer to the 13.3 Mb/s than ADSL1. |
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[[User:128.130.90.53|128.130.90.53]] 14:28, 1 April 2006 (UTC) |
[[User:128.130.90.53|128.130.90.53]] 14:28, 1 April 2006 (UTC) |
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Feel free to make appropriate modifications to that section as you see fit then. What you have described above is outside my scope of knowledge so if you feel this particular section needs a re-write to cover further (correct) technical details/explanations, feel free to update it! [[User:Larkymarky|Larkymarky]] 18:06, 7 April 2006 (UTC) |
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Revision as of 18:06, 7 April 2006
Echo cancellation section:
Your calculation of the rates is not correct - dividing by 2 is not necessary (why would you do that anyway?). The theoretical max rate of the downstream direction is about 13 Mbps (224 * 15 * 4kHz), not 7. --69.111.160.185
BTW - the standard is called ITU-T G.992.1, T for telecommunications, IIRC.
When I initially wrote that section, I took into account various sources and knowledge from my university comms course.
- From various graphs and other information, ADSL runs up to a maximum of 8Mb. It is ADSL2 which extends this to 12Mb and ADSL2+ which extends this again to 24Mb. This suggests that the calculation of rates is correct.
- I have modified the echo cancellation section with a link to Amplitude Modulation (AM) which hopefully explains the division by 2. Since G.DMT uses a form of AM called Quadrature Amplitude Modulation, it would suggest that the same properties of AM hold. Also, in your above statement, it should be 256*15*4.3125 since on a good quality line, ALL 256 bins are used for downstream, with 32 being used for upstream (with echo cancellation be used on these 32 so that these are jointly used for downstream and upstream data simultaneously). If any of this is misinformation, I am sure someone more knowledgeable than myself would have corrected that section by now (such is the reason for WikiPedia being in existence).
Hope that explains things! Larkymarky 10:12, 26 March 2006 (UTC)
No it is as User:69.111.160.185 writes above (maybe 222, if we start at carrier 33 and remove the pilot). If nothing else, should your 12 Mb/s for ADSL2 (which uses the same frequencies) indicate that your 8 Mb/s is incorrect. The data frame rate of 4kHz comes from the fact that one includes the overhead of the cyclic extension and the synchronization frame. Also note that carrier 0-6 is typically not used, even for upstream. The difference from 13.3 Mb/s down to 8 Mb/s can either be seen to come from framing overhead, FEC, and control channel overhead. Or, if you look up some early books on ADSL (or the ANSI standard), from the structure of bearer channels. In ANSI T1.413 issue 1 the maximum downstream bit-rate was when all four bearer channels where used and each bearer channel could bear 1.536 Mb/s, that is,the maximum was 6.144 Mb/s! Later on, some clever way of circumvent this was implemented, and the limit ended up being 8Mb/s instead. For ADSL2 these restrictions and the overhead for framing has been reduced and ADSL2 comes (theoretically) much closer to the 13.3 Mb/s than ADSL1. 128.130.90.53 14:28, 1 April 2006 (UTC)
Feel free to make appropriate modifications to that section as you see fit then. What you have described above is outside my scope of knowledge so if you feel this particular section needs a re-write to cover further (correct) technical details/explanations, feel free to update it! Larkymarky 18:06, 7 April 2006 (UTC)