On Mon, 14 May 2001, mike harrison wrote:
Hunter Pine:
You are aware that a good percentage of the T1's you purchase nowadays are just a pair of bonded 768 dsl lines, right? The phone companies have been doing that for over 20 years to save on copper.
Huh?
Just for starters: HDLC circuits run on different voltages, have timing and a bunch of other characteristics that xDSL never heard of.
I am confused -- HDLC is a link-level protocol which has nothing to do with voltages, and since you compare it to xDSL you can't have meant HDSL instead. If you meant T1 instead (which can carry 24 DS0s of digitized voice, PPP, or other protocols besides HDLC), remember that a POTS line has very different characteristics than an optical signal, yet aside from the last mile they are mostly carried over fiber, encapsulated in a T1 frame which is encapsulated in a T3 frame, which is encapsulated in OCx, etc. Likewise, a point-to-point T1 doesn't have much in common with an ATM PVC, yet you can carry a T1 across an arbitrarily complex ATM network using circuit emulation. (Yes, I am talking about the US system here, and I know elsewhere is different but a similar concept).
We are seeing BellSouth run 2 wire T1's, which have been working well so far. Still not DSL (approx 900mhz over POTS). --Mike--
AFAIK, the 2-wire T1s are in fact carried over HDSL to the smartjack, and the smartjack extracts the T1 -- I have two of these in my house, using Pairgain (now ADC)'s HiGain Solitaire H2TU.R402 for T1 transport. The URL of the frame describing the product line is at (minus any line breaks or spaces added along the way): http://www6.adc.com/ecom/wps?lineid=OND2737&group=T1%2bTransport%252FHiGain&EXPAND=OND50995&L=EC_List_Group_Index.html&R=WPS_Out_Hierarchy.html&ID=OND50995 This specific card is under HDSL2 RT Modules. John A. Tamplin jat@jaet.org 770/436-5387 HOME 4116 Manson Ave 770/431-9459 FAX Smyrna, GA 30082-3723