Re: ADSL and SDSL?

Robert B>> >>> Robert Anders>>>> Do you more reliably get the higher bandwidth with SDSL than with >>>> ADSL?
>>>> For example, is the CIR higher with SDSL? >>>> We are a very small business using VoIP and our connection is >>>> ADSL. People have problems hearing us but not the other way around. >>>> We were thinking of switching from ADSL over to SDSL, to see if that >>>> helps. >>>> Robert Anderson >>> ADSL is asymmetrical >> *not*necessarily* >>> SDSL is symetrical >> *not*necessarily* >> As "commonly deployed", SDSL has same speed up and down, and ADSL has >> mis-matched (almost invariably higher in the 'down' direction) speeds. >> However, I have had "symmetric rate" ADSL, and "Asymmetric rate" SDSL, >> service, at various times, from various providers. Not terribly >> common, but such services do/did exist. :) > Can you elaborate? I thought the 'A' in ADSL and the 'S' in SDSL stood > for asymmetrical and symmetrical respectively. What you're describing > seems to negate that doesn't it? What am I missing?

Your understanding of the _names_ underlying the acronyms is correct.

The names reference two different, incompatible, implementations of technology that fall under the broad categorization of 'DSL'.

The names do -not- dictate the actual link speeds in either direction. Nor the 'relationship' between them.

I don't know enough about the 'deep innards' of the specific technologies to discuss differences in detail. I'm _guessing_ that the names refer to the allocation of the available spectrum-space to the signals in each direction, Now, obviously, the 'allocation' puts an _upper_limit_ on the data-transmission rate, *BUT* nothing says that you have to be using the maximum rate within that allocation.

I know SDSL _does_ use the 'voice spectrum' bandwidth, and thus _cannot_ be shared on the same wire-pair with POTS voice service. ADSL runs totally at 'supersonic' frequencies, and thus can use 'shared' wiring. DSL ("low-pass") 'filters' are needed for shared lines to prevent 'non-linearities' (amplifiers, other bi-metallic junctions, etc.) from generating 'noise' in the voice spectrum, due to the supersonics.

I *do* know what service I have actually had.

1) 512kbit up / 512kbit down. on a non-shared line. CPE was a "Cisco 678" ADSL modem. (I'm using that _same_ modem on a 1.5mbit down/ 768k up 'shared' circuit presently.) 2) 768k down / 384k up, on a non-shared line. CPE was an Efficient Networks 'SpeedStream 5150" *SDSL* modem. (*not* a "5160", which is an identical-looking ADSL unit. :)

You can "google" up the specs of those specific modems to confirm the which type of DSL are used for.

I had numerous occasions where I saturated those links for extended periods, both upstream and downstream (at different times), to _nearby_ end-points with "big" pipes -- the speed figures above stand 'confirmed by actual usage measurements'.