dslreports logo
 
    All Forums Hot Topics Gallery
spc
Search similar:


uniqs
1105

andrewc2
join:2011-06-05
Matamoras, PA

andrewc2

Member

Cable HFC vs. VDSL Lawn Fridge boxes

I'm interested in learning the technical reasoning behind why VDSL services such as ATT UVerse require such large lawn fridges to provide service in communities where as Cable providers are able to provide similar services with a headend and small local boxes hanging of power poles.

I understand that cable is a Hybrid Fibre-Coaxial system which needs power supplies, and VDLS services such as UVerse are provided over traditional copper pairs.

So what is it specific to VDSL that requires lawn fridges as opposed to the smaller boxes cable providers are able to use for HFC?

mackey
Premium Member
join:2007-08-20

1 recommendation

mackey

Premium Member

HFC is distributed in that each customer is T'd off a single line. With xDSL, each customer gets a dedicated pair of wires back to the "lawn fridge"

/M

tschmidt
MVM
join:2000-11-12
Milford, NH
·Consolidated Com..
·Republic Wireless
·Hollis Hosting

tschmidt to andrewc2

MVM

to andrewc2
As mackey See Profile posted in a HFC network the same signal goes to all subscribers so the electronics in a node is basically about transformation of an optical signal to electrical and vice versa.

In the case of ADSL or VDSL each subscriber gets their own link. That means line drivers/receivers are needed for each line, basically a DSL modem per line. All these signals need to be multiplexed/multiplexed over the backhaul connection.

If VDSL vectoring is used to cancel noise then complex DSP functionality is needed.

Lastly in some cases speed is increased by bonding two or more VDSL connections into a faster composite circuit. That also requires extra logic.

All in all a remote DSLAM is more complex than a HFC node.

/tom

andrewc2
join:2011-06-05
Matamoras, PA

andrewc2

Member

Ah okay so it's the dedicated per user cabling and requiring management before the backbone connection.

Thanks! I appreciate the knowledge!
JoelC707
Premium Member
join:2002-07-09
Lanett, AL

2 recommendations

JoelC707

Premium Member

FWIW, cable companies do have larger power supplies they could use. There's two that come to mind that are around the Atlanta area. One is a tall "lawn fridge" that I forget the name of (made by either Alpha or Genesys) and the other is a Genesys LE2 that's more of a "chest freezer" in that it's short and squat but wide.

The taller one usually holds 2 power supply units (and two strings of batteries IIRC) to feed two different nearby nodes. The larger LE2 holds up to 4 power supplies and 4 strings of batteries. The LE2 also usually includes a built in generator as well, don't remember about the other one but most can have a standalone generator with them (with the obvious exception of the pole mounted power supplies).

Here's the thing though, these larger units are often placed out of sight (which I can attest to, can make it hard to find when you are doing maintenance on it). That helps because now you don't hear as much about their potential "lawn fridges" as they usually aren't right in someone's yard (yes, there are some power supplies that are in front yards, my yard was one of them but they aren't as big).

pike
Premium Member
join:2001-02-01
Washington, DC

1 recommendation

pike to andrewc2

Premium Member

to andrewc2
Another important consideration is distance. DSL signals can only traverse approximately 4 miles of copper before they degrade to the point of being useless. The original telephone networks were planned and built around carrying analog voice transmissions and no considerations were given to the carriage of digital signals. The central office (CO) where your copper telephone line terminates serves a geographic area far greater than 4 miles because analog signals can be easily amplified, but this is not the case for digital. The lawn fridges, or remote terminal (RT), basically brings a miniature CO (via fiber optic lines) to your neighborhood to gap the distance between your house and the CO in order to accommodate the digital DSL signal.

CATV networks use a completely different technology that's better suited to long distance transmission.

tschmidt
MVM
join:2000-11-12
Milford, NH
·Consolidated Com..
·Republic Wireless
·Hollis Hosting

1 recommendation

tschmidt to JoelC707

MVM

to JoelC707
said by JoelC707:

FWIW, cable companies do have larger power supplies they could use.

That is a good point. DSLAMs consume more power then a node so the backup power for a given amount of time will take up more space.

/tom