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To: WTC who wrote (3791)	5/19/1999 12:26:00 PM
From: Darren DeNunzio	Read Replies (2) \| Respond to of 12823

xDSL Transmission Rates This may be helpful to some. Is the VDSL rate of 2.3 Mbit/s upload correct ? Connection Method Rate =================================================== Asymmetric DSL (ADSL) 6 Mbit/s Downstream 640 Kbit/s Upstream Consumer DSL (CDSL) 1 Mbit/s Downstream 128 Kbit/s Upstream High-speed DSL (HDSL) 1.544 Mbit/s ISDN DSL (ISDL) 128 Kbit/s Rate-adaptive DSL (RADSL) 6 Mbit/s Downstream 640 Kbit/s Upstream Single-pair HDSL (S-HDSL) 768 Kbit/s Symmetric DSL (SDSL) 2 Mbit/s Very high-speed DSL (VDSL) 51 Mbit/s Downstream 2.3 Mbit/s Upstream

To: WTC who wrote (3791)	5/19/1999 12:49:00 PM
From: Darren DeNunzio	Respond to of 12823

Regarding VDSL Unknowns Does anyone know if any of these issues have been resolved, or clarified? The full text can be found at adsl.com VDSL is still in the definition stage; some preliminary products exist, but not enough is known yet about telephone line characteristics, RFI emissions and susceptibility, upstream multiplexing protocols, and information requirements to frame a set of definitive, standardizable properties. One large unknown is the maximum distance that VDSL can reliably realize for a given data rate. This is unknown because real line characteristics at the frequencies required for VDSL are speculative and items such as short bridged taps or unterminated extension lines in homes, which have no affect on telephony, ISDN or ADSL, may have very detrimental affects on VDSL in certain configurations. Furthermore, VDSL invades the frequency ranges of amateur radio, and every above-ground telephone wire is an antenna that both radiates and attracts energy in amateur radio bands. Balancing low signal levels to prevent emissions that interfere with amateur radio with higher signals needed to combat interference by amateur radio could be the dominant factor in determining line reach. A second dimension of VDSL that is far from clear is the services environment. It can be assumed that VDSL will carry information in ATM cell format for video and asymmetric data communications, although optimum downstream and upstream data rates have not been ascertained. What is harder to assess is the need for VDSL to carry information in non-ATM formats (such as conventional PDH structures) and the need for symmetric channels at broadband rates (above T1/E1). VDSL will not be completely independent of upper layer protocols, particularly in the upstream direction where multiplexing data from more than one CPE may require knowledge of link layer formats (that is, ATM or not). A third difficult subject is premises distribution and the interface between the telephone network and customer premises equipment (CPE). Cost considerations favor a passive network interface with premises VDSL installed in CPE and upstream multiplexing handled much like local area network busses. System management, reliability, regulatory constraints, and migration favor an active network termination, just like ADSL and ISDN, that can operate like a hub, with point-to-point or shared media distribution to multiple CPE on premises wiring that is independent and physically isolated from network wiring. But, costs cannot be ignored. Small ONUs must spread common equipment costs, such as fiber links, interfaces, and equipment cabinets, over a small number of subscribers compared to HFC. VDSL therefore has a much lower cost target than ADSL, which may connect directly from a wiring center, or cable modems, which also have much lower common equipment costs per user. Furthermore, VDSL for passive NTs may (only may) be more expensive than VDSL for active NTs, but the elimination of any other premises network electronics may make it the most cost effective solution, and highly desired, despite the obvious benefits of an active NT.