[clue-tech] DSL providers

[William]

Hex Star wrote:
> I find it funny how people constantly point out that neighbors share 
> the same pipe, while the same is true for any other broadband 
> connection except instead of it being shared at the neighborhood area, 
> you're sharing the data center connection...so no matter what there's 
> still a bottleneck...
This very topic is the basis for many debates.  In the hopes of avoiding 
a religious fight while helping you understand why this is "constantly" 
pointed out, I'll explain in the easiest way I can (taking liberties to 
avoid as much complexity as possible, and being verbose in the hope that 
I can head-off any anticipated questions).  For reference, I will be 
expanding the examples set forth in [Computer Networking, A Top-Down 
Approach Featuring the Internet; 3rd Edition; pages 26-28].  To brief 
the point, HFC/Cable lines are clearly defined as being "shared" while 
DSL lines are clearly defined as being "dedicated".  I'll illustrate 
why, after some definitions that will be used to draw an analogy between 
Cable and DSL.

I don't know whether you already understand the fundamental difference 
between a "network hub" and a "network switch", so I'll give a 
rudimentary contrast.  Please jump ahead if you're already clear on the 
distinction.  First, both a hub and a switch are (generally speaking) 
repeaters that enable several network devices to communicate with one 
another by repeating packets received on one line to one or more other 
lines.  They handle the repeating task differently, however:

* A hub repeats every packet it receives onto every connected line, 
verbatim.  Consequently, every network device that is connected to the 
hub must receive every single packet that is sent to/through the hub.  
Each network device simply disregards packets not destined for 
themselves.  Note that there is a time cost when disregarding undesired 
packets.  Because of this mass-broadcasting-like behavior, it is very 
easy to snoop network traffic at a hub.

* A switch however, repeats each packet only to the specific destination 
line.  Each network device connected to the switch receives only those 
packets that are sent to that specific device.  Consequently, network 
traffic is far more efficient on networks using switches than those 
using hubs.  While possible for certain types of traffic, snooping 
network traffic at a switch is not nearly as easy as snooping at a hub.

Given these definitions, I'll draw the relevant analogy to Cable and DSL 
(very loosely speaking -- this is an analogy).

* A Cable user is (effectively) connected via a hub that is shared with 
all their neighbors.  When using Cable at home, all of your neighbors 
can snoop your traffic because every packet that you send and receive is 
bounced off all of your neighbors.  The obvious consequence of this is 
that every "active" user is sending traffic to your home (doubly so when 
you consider that their output packets are hitting you *and* their input 
packets are hitting you), reducing your bandwidth capacity for as long 
as they are active.  This is why the cable line is considered "shared".

* A DSL user is (effectively) connected via a switch that is discrete to 
the line provider.  When using DSL at home, your neighbors cannot snoop 
your traffic.  Packets that you send or receive are piped strictly 
between you and your ISP.  Your neighbor's packets never hit your home, 
so they never directly affect your bandwidth capacity.  This is why the 
DSL line is considered "dedicated".

Note that the "bottleneck" to which you refer occurs at the ISP's 
internal and perimeter routers (or even higher as dictated by network 
health) where many network are combined.  These routers are massive and 
handle incredible amounts of traffic each day.  The likelihood of any 
single user significantly affecting other same-ISP users in either the 
Cable or the DSL case is negligible.  Consequently, a DSL user simply 
does not affect neighbor DSL users as much as a Cable user affects their 
Cable neighbors.

> and heh, just looked at FRII and they're a DSL provider...that IMO 
> means they're even less flexible then a cable broadband ISP like 
> Comcast because the farther away you are from their central office the 
> slower your connection which is not the case with cable broadband...
While what you say is true about DSL bandwidth rates dropping 
significantly as the end-user is positioned further and further away 
from the nearest DSL Point-of-Presence, make no mistake.  Distance 
affects the propagation rate of every line, generally manifesting as 
round-trip latency for everyone as they move further from their 
respective Points-of-Presence.  Cable is no exception.  While the 
effective bandwidth fall-off rate is slower for Cable than for DSL, the 
DSL rate is guaranteed once determined. Cable makes no such guarantee of 
bandwidth because it cannot (don't let the marketers fool you).  As soon 
as a Cable user starts downloading, their neighbors' download rate 
suffers immediately and sometimes, significantly.  Additionally, Cable 
users are faced with the question, "Do I really want my neighbors to see 
what I'm downloading?"  :)  [Yes, I'm trying to inject some humor after 
all that technical dialog.]

Hope this helps,

William


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