[NCLUG] Re: DSL Throttling or General Congestion?

[John L. Bass]

Sean Reifschneider wrote:
> This is a follow-up on an ancient thread about DSL, I think specifically in
> response to my message at:
>
> 	http://www.nclug.org/pipermail/nclug/2006-November/007256.html
>
> It seems to be providing some more details behind what I was saying, from a
> larger providers perspective (the DSL setup I ran for NCIC only handled a few
> dozen lines, because it was largely business-oriented).
>
> Sean
>   

Thanks Sean for posting that. I've also had discussions with Qwest about 
rural DSL availability, and learned a few things about how it's being 
deployed. As the speed/price competition heats up, Qwest is only able to 
offer high speed DSL close to central offices, or where there is a 
remote terminal (RT) with a fibre feed (which are rare). Most of Larimer 
county outside city limits is using RTs (PairGain systems) with copper 
T1 feeds. Copper T1's have a lot of cross-talk, so there are severe 
limits on how many you can put in a cable, as they may require some 
spare pairs to shield a T1 from other T1's and analog phone users in the 
same cable. So quite frequently, there are a shortage of rural T1's 
available after most pairs are muxed for voice services at the rural RT 
and beyond. This makes availability of copper T1's to provide DSL behind 
the copper RT's a bit hit and miss, very expensive, and certainly not at 
city CO based prices. Qwest policy appears to be only installing rural 
DSL where there is fibre because of this. Big DSLAM's at the CO have 
much better resources (OC3 feeds) than the mini-SLAMs with copper T1 
feeds, so they aggregate users with a better over subscription pool size.

Because the mini-DSLAMs are generally designed with 1-4 ATM T1's for a 
uplink/feed, it's not suprising to find the over subscription ratios 
generally fall along lines of 12:1, 24:1, or 48:1 -- typically 24:1 for 
a 48 port mini-DSLAM feed with two T1's. Peer-to-Peer, and high 
bandwidth streaming delivery chews this up pretty badly. The current 
push by certain customers for free, all-you-can-eat bandwidth for 
peer-to-peer and streaming media, doesn't play well with the other 
customers behind 24:1 over subscribed T1 muxes, like a mini-DSLAM or 
half duplex wireless mux. In rural areas, it's no uncommon for DSL to 
have bounded speeds of 256kbps to 768kbps to make the over subscription 
ratio behave in the face of a few heavy users. Any time the delivered 
bandwidth to a customer, is more than 1/4 the feed bandwidth, it's 
pretty easy to end up with queue full discards due to the statistical 
probabilities of concurrent use, even without all you can eat bandwidth 
hogs.

The CWX coop model of "everyone pays their fair share" simply requires 
that bandwidth hogs need to pay for what they eat, as everyone else 
bitches pretty loudly when the buffet table is empty or just has scraps 
left behind by the bandwidth hogs. FRII pulled out of CWX because a few 
of their techs were trashing service for everyone with first party 
shooter games that were for all practical purposes flood pings leaving 
the network saturated for hours each night. When CWX decided there 
wasn't any technical solution with WiFi to prevent the service 
disruptions they caused, Andy was certain there was a solution, and went 
off to partner with several other wireless startups. When Canopy came 
along, it's ATM like 64 byte frame Time Division Multiplexing was much 
better than WiFi, but still suffers from queue full discards easily. A 
large percentage of CWX users need stable VPN access, which drops 
connections with ANY packet loss, so CWX policies are to protect that 
VPN primary use in the CWX customer base.

Along the way, CWX has have sent a number of peer-to-peer and streaming 
video bandwidth hogs to other providers, like LP Broadband which has an 
all-you-can-eat policy to attract  customers. Over subscription falls 
down when you have a few of those customers trashing everyone elses 
service. CWX has also picked up a few customers that could not use their 
VPN's on those other providers, which is certainly a great trade for the 
coop membership.  In the end, an ISP can not hide this shift in costs 
and service quality, no matter how big the ISP is, so there will be some 
ranking of poor all-you-can-eat ISP's, and reliable pay as you go ISP's. 
Things like Netflix streaming delivery which uses all available 
bandwidth, is certainly putting a huge crunch on the all-you-can-eat 
ISP's. No longer is 35:1 over subscription possible, or even 24:1 for 
that matter, as the packet loss from these peer-to-peer and streaming 
services quickly introduces queue full based packet loss, trashing 
everyone elses service. TCP/IP backs it's window size off with packet 
loss, leaving normal users crawling with small window sizes and large 
backoff times for lost packets.

CWX continues to grow slowly, and will continue with the "everyone pays 
their fair share" model, while sending the all you can eat bandwidth 
hogs to other services. We currently exclude bandwidth lower than 85kbps 
from the quota system, which is a little more than a members actual fair 
share of our T1 feeds and network costs. At 85kbps rates, CWX users can 
transfer above 16GB a month for a flat fee. Or if they really need it 
NOW for business needs, it costs about $5/GB to use available bandwidth 
at higher speeds. CWX uses that money to pay for additional wireless 
infrastructure to support it, and additional T1 bandwidth. CWX has had a 
few high rate users migrate to their own copper T1's, after using CWX to 
build their home based business for several years. At $450/mo for rural 
bonded T1's, $30/mo for 1.5mbps DSL looks VERY attractive :)

Have fun,
John