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'.