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回复 #58 carrier 的帖子
我的那个数据不是猫或者专门的DSL软件测出来的速度，而是用下面这个网站在线测试的：
http://www.wieistmeineip.de/speedtest
鉴于http本身的限制，用这种方法测试出来的应该是实际的纯数据传输量。从整个测试过程推测，应该也是计算的实际数据传输量。大致过程应该是服务器产生指定大小的虚拟数据量，然后测试和客户端通信所需的时间。还有个证据是，我曾经还偶然测出过6Mb/s的上传速度，这更暗示了4Mb/s的带宽可能是通过设置降低某个更高标准的速度实现的，但是当线路状态很好（也或者当时Alice在调整系统，这个设置暂时失效了）时，猫可能突破这个限制。
关于DSL标准，我看了一下Wikipedia，涉及标准部分是这么说的：
ADSL standards
Standard name Common name Downstream rate Upstream rate
ANSI T1.413-1998 Issue 2 ADSL 8 Mbit/s 1.0 Mbit/s
ITU G.992.1 ADSL (G.DMT) 8 Mbit/s 1.0 Mbit/s
ITU G.992.1 Annex A ADSL over POTS 8 Mbit/s 1.0 MBit/s
ITU G.992.1 Annex B ADSL over ISDN 8 Mbit/s 1.0 MBit/s
ITU G.992.2 ADSL Lite (G.Lite) 1.5 Mbit/s 0.5 Mbit/s
ITU G.992.3/4 ADSL2 12 Mbit/s 1.0 Mbit/s
ITU G.992.3/4 Annex J ADSL2 12 Mbit/s 3.5 Mbit/s
ITU G.992.3/4 Annex L[1] RE-ADSL2 5 Mbit/s 0.8 Mbit/s
ITU G.992.5 ADSL2+ 24 Mbit/s 1.0 Mbit/s
ITU G.992.5 Annex L[1] RE-ADSL2+ 24 Mbit/s 1.0 Mbit/s
ITU G.992.5 Annex M ADSL2+M 24 Mbit/s 3.5 Mbit/s
Annexes J and M shift the upstream/downstream frequency split up to 276 kHz (from 138 kHz used in the commonly deployed annex A) in order to boost upstream rates. Additionally, the "all-digital-loop" variants of ADSL2 and ADSL2+ (annexes I and J) support an extra 256 kbit/s of upstream if the bandwidth normally used for POTS voice calls is allocated for ADSL usage.
While the ADSL access utilizes the 1.1 MHz band, ADSL2+ utilizes the 2.2 MHz band.
The downstream and upstream rates displayed are theoretical maximums. Note also that because Digital subscriber line access multiplexers and ADSL modems may have been implemented based on differing or incomplete standards some manufacturers may advertise different speeds. For example, Ericsson has several devices that support non-standard upstream speeds of up to 2 Mbit/s in ADSL2 and ADSL2+.
鉴于这些标准的理论传输上限都不是2/4/16这些最常见的德国DSL服务带宽参数，估计还是DSL服务商在接入端通过一定设置降低了相应高带宽标准实现的。
[ 本帖最后由 hooklee 于 2007-8-4 00:51 编辑 ] |
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发表于 2007-8-3 23:22
